• Governments are getting ever tougher with mining companies about damage to the environment

Sadly, in developing countries like Tanzania whete much mining takes place, laws may be less strict

• Stern controls apply to the production of wastes that may be toxie or may cause environmental

damage. Safety regulations and practices must be maintained to avoid the risk of accidental release of harmful materials.

• Mine reclamation activities are undertaken gradually with the levelling of the heaps of earth

material, replacement of the top soil with a fertile one and planting of trees in the mined out areas, Care must be taken to relocate streams, wildlife and other valuable resources. Quarries and opencast workings can be reclaimed by the process of filling the holes with solid wastes. The eroded bare soil can be conserved by planting trees and grasses to serve as soil cover, which would counteract the impacts of wind, running water, rain and animals to the soil,Reclaimed land

can have many uses such as agriculture, forestry, wildlife, habitation and recreation

• Dust levels can be controlled by spraying water on roads, stockpiles and conveyors. Other steps

can also be taken including filling of drills with dust collection systems, and purchasing additional land surrounding the mine to act as 2 buffer zone. Trees planted in these buffer zones can also minimize the visual impact of dust, from the mining operations, to local communities,

• Noise can be controlled though careful selection of equipment and insulation, and enclosures

around machinery

• The poisonous and toxie substances used in metal extraction must be treated properly before

being directed into rivers and streams. Altematively, these materials may be drained into reservoirs where they can gradually percolate deep into the soil and evaporate into the air without eausing much harm to the surrounding ecosystems. In some mines, absorbent carpets are spread on the surface of the ground to trap the toxic substances contained in liquid chemicals used for mining, hence preventing these chemicals from finding their way to water bodies,

NON METALS AND THEIR COMPOUNDS

• General Chemical Properties of Non Metals
• The non-metals are very reactive and most of them react with other elements to form

different compounds +The following are important chemical properties of non-metals which are connected with their tendency towards electron gain in the course of formation of eompounds: «1 The oxide ofa non-metal is either acidic or neutral but never basic. The oxide of a non- metal is a covalent compound. Being acidic, it combines with water to form an acid, 2 CO sy, + 1.0, 9 HCO sy Nya, + H.Oy) > 2HNO S0sg) + Hs0y+ SO.

CLO.4,+ HO, + 2HCI0,.,

• 2. A non-metal never replaces hydrogen in an acid to form a salt. This is because

replacement of hydrogen in an acid is due to the fact that H” accepts electrons supplied bya metallic atom. 2H) +28 Hay

• Arnon-metal is an electron acceptor and so cannot release electrons to hydrogen ions in

solution

‘+ 3. Non-metals form covalent chlorides, for example, the behaviour of phosphorus forming its chlorides is well known 2P + 3Chz)—9 2PCh +A covalent chloride like this is usually a volatile liquid, a non electrolyte, and rapidly hydrolysed by water.

PCloe)+ 3H.O,) > H.POs.. + 3HCL, «These properties are characteristic of non metallic chlorides (except CCl, which is not hydrolysed by water). +4 Non-metals combine with hydrogen to form many hydrides. A covalent compound is formed by equal sharing of electrons between or among the combining atoms, For

example, methane ammonia, hydrogen chloride and hydrogen sulphide are the covalent

compounds. H H 1 N-H H-C—H 1 u Ls ammonia methane H H H- cl Hs hydrogen chloride = brydrogen sulphide +5. Non-metals are oxidizing agents As discussed early, non-metals accept electrons fiom other substances. Therefore, they are called oxidizing agents because, upon accepting the electrons, the substances donating these elections are oxidized. So they act as the agents for oxidation of other substances,

• The Oxidizing Properties of Non-metals
• Explain the oxidizing properties of non-metals
• Non-metals react by gaining electrons to become negative ions. A univalent non-metal

accepts one electron while a divalent one accepts two electrons. The ion formed carries the corresponding number of negative charges, but they rarely exceed two and never exceed three Ate +X .cg.Cl+e Ct B+2e° 9B, eg.0+2e° 30)

• When a substance loses electron(s), it becomes oxidized, 1.¢. its oxidation number

increases, This is called oxidation Due to the fact that non-metals accept the electtons(s) donated by other substances, particularly metals, they are, therefore, termed as oxidizing agents, This is because by accepting the electrons, they help oxidize the electron donors

• Those substances or metals which donated the electrons are called reducing agents. This

is because the electrons they donate reduce the oxidation number of non-metals, This process is called reduction. In this respect, nor-metals act as oxidizing agents while metals act as reducing agents,

• Strong and weak oxidants
• As we have already seen, non-metals ionize by electron gain, In all eases, the extra

elecizon(s) accepted lead to the formation of negative ions. The easiness of formation of negative ions depends on the ability of an element to accept the electrons. The ability of accepting electrons is called electronegativity of an element. Some elements are mote electronegative than others,

• The order of electronegativity of some non-metals is as follows: Fluorine < Chlorine >

Bromine > lodine > Nitrogen > Carbon

• The degree of electronegativity indicates reactivity and hence oxidizing power of the

element. Elements with higher electronegativity will displace those elements with lower clectronegativity From their compounds

• Referring to the series above, fluorine will displace all the rest of the elements from their

compounds as itis more electronegative than any other element in the series. Likewise chlorine can displace bromine, iodine and nitrogen from their compounds. The displacement reaction occurs in the manner X:42V ay 2X +

• Where X is more electronegative than Y

Examples]

Cl. +2KBr— 2KCL., + Br

CL+KI—>2KC1 +1

• The higher the electronegativity the stronger the oxidant. For example, bromine is @

stronger oxidant than iodine, nitrogen and carbon,

• The Displacement of Non-metals by another Non-metal from 2 Compound.
• Describe the displacement of non-metals by another non-metal from a compound
• Non-metals in the reactivity series
• It is usefull to place carbon and hydrogen into the reactivity series because these

clements can be used fo extract metals, © Here's the reattivity series inchiding carbon and hydrogen © Note that zine and iron can bedisplacediiom theiroxidesusing carbon but not using

• How is chlorine made?

a concentrated solution of sodium chloride in water. The oxidation can be brought about by a number of oxidizing agénts, for example, lead

• When potassium permanganate is used, reaction equation is:
• ‘The poisonous nature of chlorine
• Chlorine is a useful but dangerous gas. It is very poisonous if inkaled to even a small

extent (1 part of chlorine in $0,000 parts of air causes death), Chlorine poisoning occurs when the gas is inhaled or swallowed. It reacts with water inside and outside of the body (such as water in the digestive tract and moisture on the lungs and eyes) to form hydrochloric acid and hydrochlorous acid Both of these substances are extremely poisonous.

‘+ Mast incidents of chlorine poisoning are due to ingesting houschold cleaners or bleach products. Due to its poisonous nature, chlorine was used in the World War I (1914-1918) to kill people and it caused many deaths.

‘+ The Chemical Properties of Chlorine

• Describe the chemical properties of chlorine

+L. When a litle litmus solution is poured onto a gas jar of chlorine, litmus immediately turns colourless. The gas also bleaches a damp litmus paper since the gas is acidic. ITblue litmus paper is used, it is first tumed red before being bleached. The bleaching action is ‘due to the fact that chlorine reacts with the water, forming a mixture of hypochlorous and hydrochloric acids, ‘+The hypochlorous acid is a very reactive compound and readily gives up its oxygen to the

dye, to form a colourless compound:

• Thus, dry chlorine does not bleach. It has to be moist since the hypochlorous acid formed

by its reaction with water isthe one that is responsible for the bleaching action.

• 2. Chlorine reacts with many reactive metals, on heating, giving their respective chlorine

salis,eg +3. Some non-mietals humm in chlorine to Form covalent compounds:

• (Dry, yellow phosphorous bums spontaneously in the gas to produce white fumes of

chlorides of phosphorous, mainly PC,

• 4 When a filter paper dipped into a little turpentine is dropped into a gas jar of chlorine, a

violent reaction occurs and a black cloud of solid particles of carbon is formed. ‘+ The reaction also takes place with other hydrocarbons as well and as with turpentine hydrogen chloride gas is formed. The hydrogen chloride can be shown to be present by passing a little ammonia gas across the top of the jar whereby dense white fumes of ammonium chloride are observed

• 5. Hydrogen chloride gas is oxidized to elemental sulphur by chlorine gas. When a gas jar

of hydrogen sulphide is inverted over a gas jar of chlorine, a yellow precipitate of sulphur and hydrogen chloride gas will be formed

• 6. When a stream of chlorine gas is bubbled through a pale green iron (Il) chloride

solution, a red-brown precipitate of iron (III) chloride is formed, showing that the iron

{ID chloride has been oxidized to iron (IID chloride.

• lonically
• 7. When chlorine is bubbled into the solution of sulphur dioxide in water for a few

minutes, dilute sulphuric acid is obtained. «8 The reaction between chlorine and alkalis gives products which depend upon reaction conditions:

• Chlorine reacts with cold dilute aqueous solution of sodium or potassium hydroxides,

forming a pale yellow solution of the hypochlorite and chloride of the metal

• With the hot concentrated aqueous solution, a mixture of the chloride and chlorate is

formed +A similar reaction occurs if hot concentrated calcium hydroxide solution is used

• The Uses of Chlorine
• Bxplain the uses ofchlorine
• 1 Chlorine is bleaching agent and is also used in the manufacture of other bleaches,

When chlorine is added to sodium hydroxide solution, bleach is made

• ‘The active chemical in bleach is sodium hypochlorite (sodium chlorate (1)
• If chlorine is passed for a considerable time over solid calcium hydroxide the product

formed is bleaching powder

• Bleaching power finds extensive use in dye works, and in laundries. It is used in

industries where cloth, cotton, paper, ete, need to be bleached Many textile industries use chlorine for bleaching purposes. Bleach is also used to kill bacteria for example in the toilet. It will also remove colour from the dyed materials.

• 2. Chlorine is added to water supplied to homes and industries to kill disease-causing

germs like bacteria. If they were not killed, these pathogens might cause diseases such as cholera and typhoid. It is also used to sterilize the water in swimming pools. +3. Chlorine is used to make some important chemicals such as hydrochloric acid, chloroflucrocarbons (CFCs), tetrachloromethane (C14), and chloroform (CHCI).

• CFC, are carbon compounds containing both chlorine and fluorine. An example is

trichchlorofluoromethane (CCE)

• CFC, are very uncreative compounds. They were used in aerosol cans and reftigerators

However, CFC, damage the ozone layer. Consequently, their usc is strongly discouraged. +4 Chlorine is reactant in the manufacture organo-chloro compounds which are used to make pesticides, antisepties (e.g. dettol), herbicides (weed killers) and polyvinyl chloride (PYC) which is an intermediate compound in the production of plastics.

+ Hydrogen Chloride

A Dry Sample of Hydrogen Chloride Gas

Prepare a dry sample of hydrogen chloride gas Hydrogen chloride is a gaseous compound at room temperature. It is usually prepared in the laboratory by the reaction between concentrated sulphuric acid and any chloride, e.g. sodium chloride. When a mixture of the two is gently warmed, hydrogen chloride gas is formed

Preparation of hydrogen citoride gas

‘The Properties of Hydrogen Chloride Gas Explain the properties of inérogen chloride gas

• Physical properties

Includes

• {tis colourless gas with a choking, irritating smell and an acid taste
• itis heavier (denser) than air

3._ It fumes in most air due to the formation of tiny droplets of hydrochloric acid

• It is very soluble m water (450 cm’ of gas in 1 em’ of water). ‘The acidic properties and the

solubility of hydrogen chloride gas can best be shown by the fountain experiment ) Chemical properties 1LA dry sample of hydrogen chloride gas has no effect on dry, blue litmus paper but it tums moist, blue litmus paper to red. This is due to acidic propertics of hydrogen chlorine gas 2, It does not burn and does not support combustion

• When a stream of hydrogen chloride gas is passed over sme heated metals, the anhydrous

chloride of these metals are formed.

• Ibis decomposed by strong oxidizing agents such as manganese dioxide, lead dioxide and red

lead to give chlorine gas.

• When the gas is passed though a solution of silver nitrate, acidified with dilute nitric acid, 2

white precipitate of silver chloride is formed. This is another test for hydrogen chloride gas and all soluble chlorides.

• It gives clouds of white fumes when brought into contact with ammonia vapour. The fumes

are solid ammonium chloride (NH,CI) In qualitative analysis, this is the chemical test for hydrogen chloride gas as well as for ammonia as. Reactions of aqueous hydrogen chloride Hydrogen chloride gas is very soluble in water (and in other polar solvents), In water, an acid

solution is formed, which is hydrochloric acid. In aqueous solution, the hydrogen chloride

molecule dissociates into hydrogen ions (H") and chloride ions (CI): The solution is called hydrochloric acid. Hydrochloric acid reacts with metals, metal oxides, hydroxides (soluble bases) and metal carbonates.

This suggests that when hydrogen chloride gas is dissolved in water an acidic solution is formed for example:

• ittums damp blue litmus paper red;
• itreacts with various substances just like other acids (see table bellow); and
• it conducts electricity, vielding hydrogen gas atthe eathode and chlorine gas at the anode

Reactions of aqueous hydrogen chloride Acid reacting with General equation oxide (base) acid + metal oxide @ salt + water alkali (soluble base) acid ‘metal hydroxide(akali)®salt+water Metal acid + metal ® salt + hydrogen metal carbonate acid + metal carbonateBsalt+water+CO:

The Uses of Hydrogen Chloride

Explain the uses of hydrogen chloride These are:

• Its chiefty used in the production of hydrochloric acid. When the gas is dissolved in water in the

appropriate proportions, hydrochloric acd is formed

• Aqueous hydrogen chloride is used in qualitative and quantitative analysis
• It is an important reagent in other industrial chemical transformations, ¢ g. hydrochlorination of

rubber and production of vinyl and alkyl chlorides.

• In the electronics industry, it i used to both rub semiconductor erystals and to purify silicon.
• tis used inthe textile industry, to separate cotton from wool and fluff
• In the laboratory, anhydrous forms of the gas are particularly usefal for generating chloride-

based Lewis acids.

• Itisused to remove rust fom the oxidized metals.
• It is extensively used in the manufacture of medicines and is a key substance utilized to tum

maize and other agricultural products into artificial sweeteners. Sulphur Sulphur Occurrence Sulphur is a yellow, crystalline, non-metallic solid. tis symbol is $. It has an atomic number of

• Sulphur exists in nature as a free element and in compounds.

Asa fiee element, sulpbur is found in several countties such as aly, Mexico, Japan, Poland, USA and Sicily. In its combined state, sulphur is found combined with metal ores such as galene (PbS), iron pyrites (FeS2), Copper pyrtites (CuFeS:) and zine blend (ZnS), It is also found in natural gas as hydrogen sulphide (HS, and in crude oil as organie sulphur compounds.

The Extraction of Sulphur from Natural Deposits Describe the extraction of sulphur from natural deposits Sulphur is extracted from its underground deposits by the Frasch process. The Frasch process makes use of the low melting point (119°C) of sulphur.

In this process, a hole about 30 em in diameter is bored down through the clay, sand, and limestone to the sulphur beds. This boring is lined with an iron pipe and inside the pipe, is sunk 2 device called sulphur pump. The pump consists of three concentric pipes (cylindrical pipes with a common centre) which end in a reservoir of a large diameter (sce figure bellow).

Exiraction of sulphur Down the outermost of the three pipes is forced a stream of water at about 170°C. This water must be kept at a pressure of about 10 atmospheres to maintain it in the liguid state, ie, itis superheated water, and itis hot enough to melt the sulphur. The molten sulphur flows into the reservoir at the base of the pump and is forced up to the surface. The sulphur obtained is 99.5% pute and can be used without any purification

The stages involved in the entire extraction process can be summarized as follows

• Superheated water (170°C) is pumped through the outer pipe to melt the sulphur.
• Hot compressed air (10 atm) is pumped down through the inner pipe. The combination of the hot

water and the hot air melts the sulphur. The molten sulphur, hot air znd hot water form a froth,

• The ffoth is forced to the earth's surface through the middle pipe by the compressed air
• The moiten sulphur is collected in large tanks (where the water drains off), cooled and solidified.

The Properties of Sulphur

Explain the properties of sulphur Sulphur is a relatively reactive element that readily reacts with other elements to form ‘compounds such as oxides, chlorides and sulphides. In chemical reactions, sulphur exhibits both oxidizing and reducing properties.

• Oxidizing properties of sulphur

Heated sulphur reacts with metals such as iron, copper, zinc and tin to give metal sulphides When a mixture of iron filings and powdered sulphur, in the proportion of $6 to 32, that is 7:4 (the ratio of their relative atomic masses), is heated, the two react in a highly exothermic reaction. The heat given out makes the mixture to continue glowing even afler the heating has sloped. A black or dark grey iron (1) sulphide is formed

In this reaction, sulphur sets as an oxidizing agent which oxidizes iron metal to iron (Ll) ion. Sulphur is reduced to sulphur ion Iron (1) sulphide is not attracted by a magnet since it is not magnetic. The magnetic property of iron is lost when this compound is formed.

The copper powder reacts with sulphur in the same way to form copper (Il) sulphide

• Reducing propertics of sulphur

Dilute acids do not act upon sulphur. However, sulphur is oxidized by hot concentrated sulphuric acid with the formation of sulphur dioxide In this reaction, the sulphur is oxidized by the acid to sulphur dioxide and the acid is reduced to the same substance The filter paper soaked in potassium dichromate changes from orange to green. The sulphur dioxide reduces chromium from chromium (VD) to chromium (II) When sulphur reacts with hot concentrated nitric acid, brown fumes of nitrogen dioxide are

formed, Sulphur is oxidized by hot concentrates nitric acid to sulphuric acid while nitric acid is reduced to nitrogen dioxide and water.

The Uses of Sulphur

Explain the uses of sulphur Includes

• Most of the sulphur produced in the world (90%) 15 used to manufacture sulphuric acid

Sulphuric acid is an important reagent in many industrial processes.

• Sulphur is used in the manufacture of sulphur dioxide (used in the Contact Process for the

manufacture of sulphuric acid)

• Manufacture of calcium hydrogensulphite, Ca(HSOs)> and sodium sulphite which are used for

bleaching wood straw and wood pulp in the paper industry

• Ibis also used for vulcanization of natural rubber. Rubber is usually sticky and soft. When heated

with sulphur (vulcanization), i becomes hard and strong,

• [tis used for dusting vines to prevent growth of certain kinds of fungi and also as an insecticide
• Sulphur is used in smaller quantities for the manufacture of dyes, explosives, fireworks,

sunpowder etc. For example gunpowder is a mixture of potassium nitrate, carbon and sulphur.

• Its used in the manufacture of various organic compounds such as plastics and pharmaceuticals

like sulphur oictments e g sulphadimadine, sepirin ete

• Photographic chemicals such as carbon disulphide (CS;) and sodium thiosulphate (Na;S;0s) are

made using sulphur as one of the raw materials

• Some is added to cement to make sulphur concrete. Unlike ordinary cement, this is not attacked

by the acid. So it is used for walls and floors in plants where acid is used

Sulphur Dioxide

Preparation of sulphur dioxide

In the laboratory, sulphur dioxide is prepared by heating a mixture of sodium sulphite and ditute hydrochloric acid, ‘The reaction equation is: Altematively, sulphur dioxide can be prepared by heating a mixture of concentrated sulphuric acid and copper. In this case, there is no reaction until the mixture in the flask becomes hot. "Then rapid effervescence occurs and the gas is usually collected as shown.

A dark brown mixture is left in the flask It contains anhydrous copper (If) sulphate and certain impurities

The Properties of Sulphur Dioxide

Describe the properties of sulphur dioxide Physical properties These are 1, The gas is colourless with an imitating (pungent), chocking smell

• tis denser than air, Its density is 2% times that of ait.

3._ It is readily soluble in water and forms an acidic solution of sulphurous acid. Acidic characteristics of sulphur dioxide As indicated above, sulphur dioxide gas dissolves in water to form an acid solution of sulphurous acid, H5S0;. The solution tums blue litmus paper red. Sulphur dioxide is thus an acidic gas.

Chemical properties The reaction characteristics described below explains the chemical properties of sulphur dioxide sas. ‘The reducing properties of sulphur dioxide

• Reduetion of dyes in flower petals or colour in paper (bleaching)

Sulphur dioxide bleaches the cotours in dyes such as flower pigments. When the flower pigments or dyes contain oxygen, they are coloured. Sulphur dioxide reduces the dye (removes oxygen From it) and the dye, therefore, turns colourless, This process can be summarized as follows, In this process, sulphur dioxide dissolves in water to form sulphurous acid: Then the acid takes up oxygen fiom the dye of the Mowers or paper and forms sulphurie acid

The removal of oxygen from the dye converts it to a colourless compound: However, the oxygen from the air may oxidize the reduced colourless compound back to the ‘original coloured compound.

(ii) Reduetion of nitrie acid If sulphur dioxide gas is bubbled through concentrated nitric acid, brown fumes of nitrogen dioxide gas are formed The nitric acid is reduced to nitrogen dioxide and the sulphur dioxide is oxidized to sulphuric acid (iii) Reduction of acidified potassium permanganate solution Sulphur dioxide decolourized purple potassium permanganate solution Sulphur dioxide is first converted to a sulphite (SOs*), after reacting with water, and then

onidized t0 4 sulphate (SO) by the permanganate The ionic equation is The oxidation state of manganese changes from +7 to *2. This isa reduction reaction (iv) Reduction of acidified potassium dichromate solution When sulphur dioxide is mixed with potassium dichtomate (VI) solution the orange colour of the solution changes to green, The dichromate (VI) is reduced to chromate (III) whieh is green in colour when in aqueous state

The oxidation state of chromium changes from +6 in potassium dichromate (VI) to +3 in chromic sulphate On the other hand, sulphur dioxide is oxidized by the dichromate (V1) to sulphate ($0.7).

Other reduction reactions involving sulphur dioxide gas Sulphur dioxide reduces chlorine, bromine and iodine to the hydrogen halides inthe presence of water: In all these cases, the solution changes fiom brawn to colourless The oxidizing properties of sulphur dioxide

• Oxidation of hydrogen sulphide

Iron (II) sulphide reacts with dilute hydrochloric acid to produce hydrogen sulphide gas and iron (UD chloride: Hydrogen sulphide gas has a smell similar to that of @ rotten egg. The hydrogen sulphide gas is ‘oxidized by sulphur dioxide in the gas jar to sulphur: The sulphur produced is a yellow residue The reaction takes place in the presence of moisture which acts as a catalyst. That is why water is added in the jar.

(ii) Oxidation of magnesium When burning magnesium is lowered into a jar containing sulphur dioxide gas, a white solid, magnesium oxide, and yellow pieces of sulphur are formed: Tests for sulphur dioxide gas Includes

• The gas ean be identified by its characteristic pungent and choking smell

2 It can also be detected by putting into ita filter paper that has been previously dipped into, an acidified solution of potassium dichromate (VI). The colour of the filter paper changes From orange to green due to the eduction of dichromate (VI) to chromate (IID).

• Sulphur dioxide also decolourized acidified potassium permanganate solution

The Uses and Hazards of Sulphur Dioxide Explain the uses and hazards of sulphur dioxide Sulphur dioxide has got a number of uses in daily life However, there are also some havards which can be caused by the gas if ts production is not controlled

Uses of sulphur dioxide

The following are some uses of sulphur dioxide gas

• The gas is used in the industrial manufacture of sulphuric acid in the Contact Process.
• Its used asa bleaching agent for wood pulp, silk, wool and straw.
• Its poisonous nature makes ita useful fumigant. So itis used in fumigation. The gas is poisonous

to all organisms, particularly bacteria

• {tis used asa preservative and sterilizing agent in making soft drinks and jam, and in dried fruits

Avery low concentration of the gas in food prevents fermentation as it stops the growth of bacteria and moulds. lis reaction with oxygen prevents oxidation of juices and other liquids to Which itis added for preservation.

Hazards of sulphur dioxide gas ‘The havards of sulphur dioxide gas are due to its effect in environmental pollution and the health problems accompanied with that pollution. Sulphur dioxide is a major air pollutant. The major sources of sulphur dioxide in the air are power plants that use fossil fuels such as coal, diesel and petrol; industrial boilers; and exhaust emissions from motor vehicles. The gas is also produced

during metal smelting and other industrial processes Half of sulphur dioxide output comes from burning coal in coal-fired power stations. All coal contains small amounts of sulphur. So when the coal is burnt to produce energy, the sulphur in the coal reacts with oxygen in the air to produce sulphur dioxide Sulphur dioxide isa very imitating gas and is thought to be the cause of bronchitis and other lung diseases. Exposure to higher concentrations of the gas can eause impairment of the respiratory

function and heart diseases. Sulphur dioxide also causes acid rain. This occurs when the gas comes in contact with moist air The sulphur dioxide dissolves in water vapour from the clouds and combines with oxygen from the atmosphere to form an acid — sulphurie acid Acid rain damages the leaves and barks of plants making them more vulnerable to diseases, weather and insects, When acid rain reaches the lake, river or other water bodies it makes the

whole water body acidic, Even a low concentration of acid in the water can kill fish and other marine organisms

Sulphuric Acid

The Contact Process for the Manufacture of Sulphuric Acid Describe the contact process for the manufacture of sulphuric acid Sulphuric acid is an important laboratory and industrial reagent. It is produced in large scale through the Contact Process. The process involves four major stages. These are: 1, production of sulphur dioxide;

• purification of sulphur dioxide;

3._ catalytic conversion of sulphur dioxide (S02) to sulphur trioxide (S03); and

• conversion of sulphur trioxide to sulphuric acid

1, Production of sulphur dioxide The sulphur dioxide used in the Contact Process can be obtained from different sources. ‘These include:

• Burning sulphur in air

This is the most convenient method of producing sulphur dioxide

• Burning sulphide ores such as iron pyrite (FeS2) and zine blend (ZnS) Sulphur dioxide gas is

produced as a by-product

• Purification of sulphur dioxide

The sulphur dioxide produced in the first stage is mixed with air, ready for passing it over the catalyst. Before contaet with the catalyst is allowed, the gas mixture has to be purified to remove impurities. This 1s achieved by passing the mixture through an electrostatic preeipitator to remove any dust. It is then washed with water to remove impurities such as traces of arsenic (III) oxide (As,05). The gas mixture is then passed through concentrated sulphuric acid to remove all

moisture The three impurities (As:0s, dust and moisture), if not removed, will poison the catalyst thereby rendering it useless

• Catalytic conversion of sulphur dioxide to sulphur trioxide

The purified and dried mixture of sulphur dioxide and air is passed through a heat exchanger to acguite the necessary heat for the conversion to sulphur trioxide. The mixture is then taken to the conversion chamber. which contains a catalyst. ‘The catalyst used is finely divided vanadium (V) oxide (vanadium pentoxide, V0.) which is heated to 450°C.

Originally, platinized asbestos was used as a catalyst. But, compared to vanadium (V) oxide platinum is very expensive and easily poisoned by impurities. So it has been replaced by vanadium (V) oxide as the usual catalyst used in the Contact Process.

Sulphur dioxide remains in contact with the catalyst during the conversion process, hence the name Contact Process. The reaction that takes place during the conversion is The conversion takes place at a temperature of 450°C and normal atmospheric pressure (1 atm), The reaction is exothermic, which means that, as sulphur trioxide is formed, heat energy is released. Ifthe temperature rises above 450 the yield of sulphur trioxide decreases

‘Once the reaction has started, no extemal heating is required, Thus, the heat exchanger maintains the temperature at 450°C. According to Le Chatelier’s principle, a lower temperature should be used to shift the equilibrium to the right, hence increasing the percentage yield, However, too low temperature will lower the formation rate to an economical level, Hence, to increase the rate, high temperature (450°C), medium pressure (1-2 atm) and a catalyst (V;0-) are used to ensure

maximum yield. The catalyst only serves to increase the rate of reaction as it does not change the Position of the dynamic equilibrium. About 98% of the possible yield of sulphur trioxide is obtained.

• Conversion of sulphur trioxide to sulphuric acid

The sulphur trioxide from the conversion chamber is passed through a heat exchanger to remove ‘excess heat. tis then faken to an absorption tower where itis dissolved in concentrated sulphuric acid to form oleum or fuming sulphuric acid: Oleum is then carefully diluted with the correct amount of water to give ordinary concentrated sulphuric acid: Sulphur dioxide cannot be dissolved direetly in water to form sulphuric acid. The reaction is so

highly exothermic that the heat produced vapourizes the sulphuric aeid formed. This makes it difficult to collect the gas because the acid vapour (mist) produced is very stable and cannot be condensed.

The flow diagram for the manufacture af sulphurie acid is show in the figure below A flow diagram of the Contact Process ‘The Properties of Sulphuric Acid Explain the properties of sulphuric acid Chemical properties of dilute sulphurie acid Dilute sulphuric acid reacts with metals, metal oxides, metal hydroxides and metal carbonates and hydrogencarbonates to produce salts Reaction with metals Dilute sulphuric acid reacts with many metals above hydrogen in the activity series to form

sulphates and hydrogen gas, €.g Reaction with metal oxides Reactions of metal oxides with dilute sulphuric acid are neutralization reactions. Metal oxides react with dilute sulphuric acid to form a salt (sulphate) and water, e.g Reaction with metals hydroxides The reaction between dilute sulphuric and a metal hydroxide is a neutralization reaction. Metal hydroxides react with dilute sulphuric acid to form a sulphate and water, ¢ g

Reaction with metal carbonates and hydrogencarbonates Dilute sulphurie acid reacts with meial carbonates and hydrogencarbonates to give metal sulphates, carbon dioxide and water, € 2 Chemical properties of concentrated sulphurie acid Concentrated sulphuric acid as a dehydrating agent As a dehydrating agent, it will remove the elements of water (hydrogen and oxygen) from @ ‘compound to form a new compound, It will dehydrate sugar, paper and wood, These are all made

‘of carbon, hydrogen and oxygen. The acid removes the hydrogen and oxygen as water, leaving carbon behind, When concentrated sulphuric acid is added to sugar, a vigorous reaction occurs, causing the reaction mixture to rise and fil the beaker The colour of the sugar changes to brown and finally black. Concentrated sulphuric acid dchydrates sugar (glucose) by taking away the elements of water (hydrogen and oxygen) from

the suger, leaving carbon, The acid will also dehydrate suerose to form carbon The final product is a black mass of carbon. The reaction is highly exothermic ‘The heat produced evaporates the water formed from the reaction, The acid also dehydrates some hydrated salts. When concentrated sulphurie acid is added to hydrated blue copper (11) sulphate crystals, the colour changes from blue to white. The acid <dehydrates the hydrated copper (Il) sulphate erystals to anhydrous copper (Il) sulphate powder:

Concentrated sulphuric acid also dehydrates methanoic acid and ethanol to give carbon monoxide and ethene gases respectively Concentrated sulphuric acid as a drying agent As a drying agent, concentrated sulphuric acid absorbs traces of water from substances. Because of its ability to absorb water, it is used for drying most gases prepared in the laboratory that it would not react with, It cannot be used for drying ammonia, carbon dioxide, hydrogen sulphide

‘or any gas with which it reacts, Sulphuric acid as an oxidizing agent Hot concentrated sulphuric acid is a strong oxidizing agent. It oxidizes both metals and non- metals while itis reduced to sulphur dioxide Concenitated sulphuric acid oxidizes charcoal (carbon) 10 carbon dioxide, sulphur to sulphur dioxide and copper to copper (Il) sulphate With sulphur and copper, the orange colour of the dichromate (V1) paper changes to green. This

confirms the presence of sulphur dioxide gas. With carbon, a white precipitate is formed on the glass rod when the rod dipped in lime water (calcium hydroxide) is placed in the mouth of the test tube. This confirms the presence of carbon dioxide gas which reacts with the calcium hydroxide on the glass rod to produce a white precipitate of calcium carbonate ‘The Uses of Sulphuric Acid Explain the uses of sulphuric acid

Sulphuric acid is one of the most important industrial chemicals, It has widely varied uses and plays some part in the production of nearly all manufactured goods. The following are some of the uses of sulphuric acid 1, Manufacture of fertiticers The major use of sulpburie acid is the production of fertilizers such as ammonium sulphate and superphosphates (phosphate fertilizers)

• Manufacture of chemicals \t is widely used in the manufacture of chemicals eg. in making

hydrochloric acid, nitric aeid, phosphoric acid, sulphate salts, synthetic detergents, soap, paints and pigments, explosives, plastics and drugs.

• Refining of crude oil A large quantity of sulphuric avid is used in refining crude oil

4, Extraction and manufacturing of metals Sulphuric avid is used i the iron and steel-making industry to remove rust and scale from the surface of the rolled iron sheets. It is also used in processing metals e.g. m pickling (cleaning) iron and steel before plating them with tin or zine to produce galvanized iron

• Manufacture of alum Sulphuric acid is used in the manufacture of aluminium sulphate, which is

used in water treatment plants to filter impurities and to improve the taste of water. Aluminium sulphate is made by reacting bauxite with sulphurie acid

• Manufacture of natural and man-made fibres Sulphuric acid is used for making natural and

synthetic (artificial) fibres. For example, the textile called rayon 1s made from cellulose fibres derived from wood. These fibres are dissolved in a solution of tetraamminecopper (II) sulphate to produce a thick liquid which is then injected into sulphuric acid to form rayon fibres.

• Other uses Sulphuric acid is used as (i) an electrolyte in lead-acid batteries, which are used in

cars, to allow the flow of electrons between the plates in the battery. The sulphuric acid used in this way is called battery acid; Gi) as a general dehydrating agent in its concentrated form in tanning leather; and (iif) in waste water treatment Nitrogen Occurrence Nitrogen makes about 78% of the air by volume. The element also occurs combined with other compounds in the form of sodium nitrate, Chile salipetre, NaNO (as a mineral deposit in Chile),

and in the soil as ammonium sulphate, sodium nitrate, potassium nitrate and calcium nitrate Combined nitrogen also occurs as a constituent of all living matter of plants and animals in the form of proteins, enzymes, alkaloids,

Preparation ofa sample of Nitrogen in the Laboratory

Prepare a sample of nitrogen in the laboratory Nitrogen can be prepared in the laboratory by either separating the gas fiom the air or by heating ammonium nitrite

• Preparation of nitrogen by the action of heat on ammonium nitrite

The reaction between sodium nitrite and ammonium chloride gives sodium chloride and ammonium mitrite {A solution of ammonium nitrite readily decomposes, on slight warming, o give nitrogen gas.

As the solution becomes warm, rapid effervescence occurs as more nitrogen is given off. The nitrogen evolved may be collected over water because the gas is only slightly soluble in water, at ordinary temperature, and slightly denser than air Tests for nitrogen gas Aim: To test for the presence of nitrogen Procedure Using the four gas jars of nitrogen gas collected in the previous experiment (Experiment 1.16).

carry out the following tests for nitrogen ss and write down your observations:

• Remove the cover fiom the first jar and smell the gas, Observe the colour of the gas and identify

its smelt

• Remove the cover from the second jar and put in ita piece of damp universal indicator.
• Place a lighted splint into the third gas jar.

4, To the fourth jar, add some calcium hydroxide solution (lime water) and shake. Observations and inferences

• The gas is colourless and odourless. This distinguishes it fiom gases such as sulphur dioxide,

ammonia, hydrogen chloride, ete.

• The colour of the mdieator does not change. This shows that nitrogen is @ neutral gas
• The lighted splint is extinguished and the gas does not burn. It can not, therefore, be any gas

which supports combustion, eg. oxygen, dinitrogen oxide, or any combustible gas, e.g. hydrogen sulphide, carbon monoxide, hydrogen, ele

• Aller the above tests, the only gas with which nitrogen may be confused is carbon dioxide: To

distinguish it from carbon dioxide, the gas is dissolved in calcium hydroxide solution. Nitrogen leaves the calcium hydroxide unchanged while carbon dioxide turns the solution milky (due to

formation of a precipitate of CaCO:).

Properties of nitrogen

Physical properties Nitrogen is colourless and odouriess. It is slightly less dense than air and sparingly insoluble in water. The gas is neutral to litmus Chemical properties Under ordinary conditions, nitrogen gas is inert. However, the gas only takes part in reactions at very high temperature as follows:

• Itreacts with red hot metals, like magnesium and caleium to form nitrites
• Nitrogen does not burn nor does it support combustion. When heated, the gas combines with

oxygen to form nitrogen monoxide gas:

• At ordinary pressure and moderately high temperatures, nitrogen reacts with hydrogen in the

Haber Process to produce ammonia:

The Uses of Nitrogen

Explain the uses of nitrogen Here are some uses of Nitrogen 1, Manufacture of fertilizers: Nitrogen is used to manufacture nitrogenous fertilizers. ‘These include diammonium phosphate (DAP), caleium ammonium nitrate (CAN), ammonium superphosphate (ASP), ammonium nitrate (AN), ammonium phosphate sulphate (APS), ammonium sulphate nitrate (ASN), ammonium sulphate (AS) and urea 2 Refrigeration: Because of its low boiling point (-1960C), liquid nitrogen is used as a refrigerant

for storing organs in research laboratories, bull semen for artificial insemination, eggs and other calls for medical research and reproductive technology, ete, It is also used for preservation of food products and for their transportation.

• Processing reactive substances: Some reactions require an inett atmosphere in order to proceed

as desired, Because of its low reactivity, nitrogen is used to provide an inert atmosphere for storing and processing reactive substances.

• Manufacture of nston: Nivogen is used in the manufacture of synthetic fibres such as

polyamides, Polyamides are commonly known as nylons. Nylons are chemically inert and are stronger than tural fibres. They ate used in making fishing nets, clothes, ropes, and many other items

• Manufacture of ammonia: Nitrogen is used in the manufacture of ammonia through the Haber

Process In the Haber Process, ammonia is manufactured hy direct combination of nitrogen and hydrogen Nitrogen and hydrogen are mixed in the ratio of 1:3. The gases are then reacted together at a temperature of about 450°C and a pressure of 250 atmospheres in the presence of finely divided iron as a catalyst. N2(g) + 3112(g) #2NH3(g) + heat The gases are cooled while still under pressure and ammonia is removed as a liquid

• Manufacture of nitric acid: The ammonia gas manufactured using nitrogen in the Haber

Process is used in the manufacture of nitric acid by catalytic oxidation,

• Plant nutrition: When atmospheric nittogen is fixed into the soil by bacterial actions, it

becomes a nutrient to plants. Nitrogen fixation refers to the conversion of atmospheric nitrogen, by certain species of bacteria, into nitrites. Ammonia

Preparation of Dry Sample of Ammonia Gas in the Laboratory

Prepare a dry sample of ammonia gas in the laboratory Ammonia is a binary compound of nitrogen and hydrogen. Ammonia gas is eolourless and has @ sirong pungent and ehoking smell, It does not occur free in air, but exists in nitrogenous organic materials such as hoofs and horns of animals. The gas can be released by heating or burning these materials, Laboratory preparation of ammonia Ammonia is prepared in the laboratory by heating any ammonium salt with an alkali. In most

‘eases, ammonium chloride and calcium lnydroxide (the cheaper alkali) are used. Both are solid s0 they must he thoroughly ground first to give a very fine mixture so that the reaction can occur efficiently Ca{OH)ag) + 2NH Ch, +CaC 12, + 2H:09) + 2NHs Calcium hydroxide reacts with ammonium chloride to produce ammonia gas, calcium chloride and water. The flask is tilted to prevent any condensed water formed from running back into the

hot flask, which might break it Ammonia gas is dried by passing it over quicklime because it reacts with all the usual drying agents. Concentrated sulphuric acid is acidic and would absorb the gas forming a salt e.g 2NHygy+ HoSOsqy -» (NHs):SOa It reacts with ealeium chloride, forming solid complex compounds, e.g. $NHy,) + CaCl >

CaCh SNH

‘Ammonia is less dense than air and very soluble in water, soit is collected as shown by upward elivery (or downward displacement of air) Ammonia is on alkaline gas and it turns wet, red litmus paper blue

The Properties of Ammonia

Describe the properties of ammonia

Physical Properties of Ammonia

• Its colourless poisonous gas with a strong chocking simell
• tis less dense than air

3._ Ibis easily liquefied by cooling to -33°C or by compressing it

• It tums wet, red litmus paper blue as itis the only common alkaline gas
• tis very soluble in water forming alkaline solution, Ammonia has the highest solubility of all

known gases, About 800 volumes of the gas dissolve in 1 volume of water at 15%C. The fountain experiment below demonstrates this solubility Chemical properties of ammonia Reaction with air and oxygen Ammonia will not normally bum in air but can be made to do so in two ways: a. Buming ammonia in an oxygen-rich atmosphere: and b. Use of a catalyst Burning ammonia in oxygen-rich air When ammonia is bumed in air enriched with oxygen, the products formed are nitrogen and

water. ANH) + 302g) 2Nag) + 61:0, Using a eatalyst The source of ammonia gas in this experiment is concentrated ammonia solution which gives off fumes of ammonia gas. If some concentrated ammonia solution is left in a stoppered flask for 2 Few minutes, the flask will quickly become full ofammonia gas by diffusion The eatalyst used is the metal platinum. The platinum coil is heated in a bunsen flame until itis red hot. It is then lowered into a flask containing ammonia. The coil continues to glow even

though it is not being heated. This indicates that a chemical reaction is taking place. Near the top of the flask brown fumes can be seen The products of this reaction are nitrogen monoxide (nitrogen (II) oxide), which is a colourless gas, and water

ANH) +50) + AND) + 64:0.)

However, as the nitrogen monoxide gas moves towards the neck of the flask and comes into contact with the air, it reacts with the oxygen in the air wo form nittogen dioxide gas whieh is brown in colour. Hence, the brown Furnes are seen at the neck of the flask 2NO Wy + x4) + 2NOIe) Reaction with copper When ammonia gas is passed over heated copper (Il) oxide, the gas is oxidized to nitrogen and water by the hot copper (II) oxide while the oxide is reduced to copper.

3CUOs)~ INH + 3Ctly) + 3HOp) + Nays Copper (Il) oxide is black During the reaction it is oxidized to copper which is reddish brown in colour. Reaction with hydrogen chloride gas When ammonia and hydrogen chloride are mixed, dense white fumes of ammonium chloride are formed.

Nii + HCl) + NHC This test is simply performed by dipping a glass rod into concentrated hydroehlorie acid then holding the glass rod at the mouth of a gas ar containing ammonia gas.

The Uses of Ammonia

Explain the Uses of Ammonia Manufacture of fertilizer Since ammonia solution is alkaline, it reacts with acids to form ammonium salts whieh are used as fertilizers. Other nitrogenous fertilizers manufactured using ammonia melude ammonium sulphate nitrate (ASN), diammonium phosphate (DAP) and calcium ammonium nitrate (CAN) Ammonia itself can be used directly as a fertilizer but has three disadvantages:

• Ammonia comes as a gas or a concentrated solution which is less easy to store; itis easier to

store the solid ammonium salts,

• Ammonia is alkaline and can affect the natural pH of the soil
• Ammonia easily evaporates if directly applied to the sol.

Manufacture of nitric acid Alot of the ammonia from the Haber Process is used to make nitric acid. The raw materials for manufacture of nitric acid are ammonia, ait and water The overall result is that ammonia is oxidized to nitric acid Cleaning Ammonia solution is very uscful in cleaning. This is because it softens water in homes and laundries and neutralizes acid stains caused by perspiration, hence making washing easier. Itis

also used as a grease solvent Refrigeration Liquid ammonia is used in large-scale reftigerating plants sueh as in ships and warehouses. It used to be used in domestic reffigerators, but has now been replaced by non-toxie, non-corrosive chloro fluorohydrocarbons (CFHs) Manufacture of synthetic fibres In the textile industry, ammonia is used in the manufacture of synthetic fibres such as nylon and Carbon ‘The Forms in which Carhon Exists

Name the forms in which carbon exists Although carbon forms less than one percent of the earth's crust by weight, it is the most interesting of all elements, This 1s because of the following reasons

• All living things are made of carbon and its compounds.
• Over % of the world’s power is obtained from carbon and its compounds.
• Over % of all substances in the world are made of carbon.

Carbon is not commonly found in a fiee state. The free element is mainly found as graphite and diamond, Carbon occurs in a number of other forms, ¢.2. wood charcoal, animal charcoal, coke, soot (lampbiack) Carbon compounds are found in many naturally occurring substances such as coal, petroleum, wood, coal gas, natural gas, carbonates, shells, organic matter of all kinds, all living things, and ‘occurs in the air to a small, but very important extent (0.03 — 0.04% by volume) as carbon

dioxide. The carbohydrates, proteins and lipids in ll living things contain carbon Pure carbon is found in the form of diamond in Tanzania (Mwadui), Sierra Leone, India, South Africa, Russia and South America; and impure earbon, as graphite, is found in Sri Lanka.

Allotropie Forms of Carbon

Describe allotropic forms of carbon An element that exists in more than one form is said to exhibit allotropy. Allottopy is the existence of an element in more than one form (without change of state). ‘The various forms are known as allotropes, Allotropes ofa given element differ in their physical properties and may differ in some chemical properties as well. The allotropic forms of carbon are: a graphite: b. diamond; and

©. amorphous carbon These allotropes have got different molecular structures. The structural differences are mainly due to the way their atoms are packed. Graphite Graphite has a layer structure. Figure 1.18 illustrates one layer of the structure of graphite. Each layer consists of earbon atoms covalently bonded together into hexagonal rings. These rings form flat parallel layers, one over the other. ‘The force that hold the carbon atoms together are very

strong. Adjacent layers are held together by weak van der Waals” forves as shown in figure 1.19 The layers readily slide over one another, accounting for the soft and greasy texture of graphite, Carbon atoms in one graphite layer Graphite structure Carbon atom has got four electrons in its outer shell. Bach carbon atom forms three covalent bonds to other carbon atoms. Thus, three of its four outermost electrons are paired up to form

covalent bonds The fourth electron is not attached to any particular atom (delocalized) and is free to move anywhere along the layers. Graphite conducts electricity in the plane of the layers but not at right angles to them.

Because conduction of electricity mvolves movement of unshared electrons from one atom to another atom, graphite is a good conductor of electricity since the hexagonal layers permit this movement It is also a good conductor of heat for a similar reason.

Physical properties of graphite

• Itis a black, soft and slippery substance. It feels soapy and greasy. It has a metallic lustre and is

‘opaque to light 2 It has low relative density (2.3) as compared to diamond (3.5)

• Graphite is a good conductor of heat and electricity due to the delocalized electrons
• [thas a very high melting point (3730°C) and boiling point (4830°C). The melting and boiling

points are high because of strong covalent bonds between the carbon atoms which require more energy (heat) to break in order to melt graphite

Uses of graphite

• It is used as an electrode in electrolysis and as a positive terminal in dry cells. The use of

araphite as electrode in electrolysis has an advantage because it does not react readily with most substances (it is an inert electrode)

• It is used as a lubricant, particularly when high temperatures are involved, where the usual

lubricating oils easily decompose due to extreme heat. It is a lubricant for dynamos, electric motors and fast-moving parts of machinery

• The major use of graphite is in making lead pencils of different hardness, by mixing it with

different proportions of clay. The weakly held layers of carbon atoms in graphite easily slide ‘over each other and are left behind on paper as black marks

• Being resistant to chemicals and having a high melting point and also because it is a good

conductor of heat, graphite is used to make erucibles.

• Graphite has the ability to absorb fast-moving neutrons, thus, it is used in nuclear reactors to

ccontrol the speed of the nuclear fission reaction. Diamond The basic unit of the diamond structure is shown in figure 1.20. Each carbon atom is covalently bonded to four other carbon atoms ‘This basic unit is repeated in three dimensions as shown in gure 1.21 to form a giant tetrahedral structure of millions of carbon atoms, all forming four covalent bonds to each other. The melting point of diamond is high. This is because of the strong

covalent bonds between carbon atoms, which require a large amount of heat energy to break up. Physical properties of diamond

• [tis the hardest natural substance known. This due to the strong covalent bonds between the

carbon atoms in diamond, Again the compact tetrahedral arrangement of carbon atoms contributes to its hardness,

• Ithas the highest melting point (3550°C) and boiling point (4289°C).
• Ithas 2 high relative density (3.5) compared to graphite (23)
• It is a poor conductor of heat and electricity. This is because thete are no fiee electrons 10

conduct electricity. Al electrons are firmly held in covalent bonds,

• tis colourless, transparent and bas a dazzling (amazing) brillant lustre and radiance.

6 Ithas @ high refractive index of 2.5. The high refiactive index results in high dispersion of Tight making it suitable for use in jewellery.

Uses of diamond

• {tis used in making jewellery
• Due to its extreme hardness, its used to make glass cutters, dilling devices, rock borers, and as

an abrasive for smoothing very hard materials. Comparison of the properties of diantond and graphite

Diamond Graphite

• Colourless, transparent andglitering Black, opaque with metallic lustre

2 Hardest natural substanceknown, used 10 Soft to touch, greasy or soapy, can be used as a cut glass andin dail lubricant and in making lead pencils

• High relative density (3.5) Low relative density @.3)
• Nomconductor Good conductor of heat and eleetrcity
• Bums in air Feast realy (atabout 900°C) Bums in air readily (at 700°C)

Have strong C-C bonds within the hexagonal rings

• Have strong C-C covalenthonds arranged ;

neon entircreag. i He SBE Buk weak Van der Wal’ forces in octahedrally toform a giant molecular ery an between layers

• ls cleavage is difficult and occurs along Cleavage easy, and occurs along the sheets or the

the hounderes ofthe octahedral crystal unit layers 8 Prepared ffom graphite at very high Prepared from coke and siliea mixture at high pressure snd temperstare temperature

• Not attacked by potassiumchlorate and

‘Auacked by these reagents nitric acid together A proof that diamond and graphite are both allotropic forms of carbon can be shown experimentally by burning equal masses of each allotrope in a stream of oxygen. tis Found that equal masses of cach allotrope produce equal masses of carbon dioxide. Cjy + Oxy) ~* COng) ‘The weight of carbon dioxide produced can be determined by allowing it to be absorbed in a weighed amount of potassium hydroxide solution, 2KOH\ay + COs) KxCOsay + 1:04

Then, the weight of carhon dioxide is obtained by calculations based on the equation above Amorphous carbon Amorphous carbon is carbon that does not have any clear shape, form or crystalline structure.

Amorphous carbon is made of tiny bits of graphite with varying amounts of other elemenis considered as impurities. It is formed when a materials containing carbon is bumed in a limited supply of oxygen, resulting in incomplete combustion.

Amorphous carbon exists in many forms. The following are the major forms in which it oceurs a Charcoal . Lampblack (soot) or carbon black ©. Coke Charcoal ‘Charcoal 1s made by heating organic material (animal or plant parts) to @ high temperature i the absence af air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents. This process is called destructive distillation, There are three categories of charcoal,

namely, wood chareoal, animal chareosll and sugar chareoal Wood charcoal Wood charcoal is made by heating wood or other vegetable matter (for example coconut shells) im the almost complete absence of air. Wood charcoal is light, porous and is a remarkably good absorbent for liquid oF gases (1. em of wood charcoal will absorb 100 em3 of ammonia gas at we)

Uses of wood charcoal

1, Because of its ability to absorb large amounts of gas or liquid, i is used in gas masks to absorb poisonous gases in air in industrial process to recover volatile materials from waste gases,

• Wood charcoal can be used in metal refining instead of coke.
• Wood charcoal is a good source of energy. Thus, itis used as fuel for cooking and heating in

homes, Animal charcoal Animal charcoal is made by heating animal bones in the absence of air. Its main component is calcium phosphate, Ca3(PO4)2, and carbon constitutes about 10% of the components

Uses of animal charcoal: It is used in sugar industries to remove the colouring matter from brown

sugar to make it white Sugar charcoal Sugar charcoal is a very pure form of earbon, and is made by removing the elements of water (oxygen and hydrogen) from sugar This is achieved by using strong dehydrating agents such as concentrated sulphuric acid or concentrated nitric acid, which removes water from sugar,

Uses of sugar charcoal: Sugar charcoal is chiefly used in the manufacture of artificial diamonds

Lampblack/sooticarbon black This is produced by burning petroleum or any hydrocarbon in a limited supply of air (or in chlorine). It cam also be produced from the buming of organic material at home. It is commonly found in the kitchen chimneys, lamps and on bases of cooking pans and pots

Uses of lampblack/soot/carbon

• {tis used in making printers’ ink, shoe polish and carbon papers.
• tis an important industrial material in the manufacture of tyres. It is used as a filler material in

tyres Coke Coke is made by destructive distillation of coal. During the process, coal is obtained as the major product The other products formed when coal is destructively distilled are coal gas, coal tar, coal oil, 228 carbon and ammonia liquor.

Uses of coke

• Coke is used as a fuel and as a reducing agent in the extraction of iron, lead and zine. Wis also

used as a fuel in boilers.

• It is used in the manufacture of producer gas and water gas.

‘Chemical properties of carbon

• Carbon bums in excess oxygen to form carbon dioxide C+ Oni —> COsiy In insufficient

oxygen, carbon monoxide is formed 2Cj + Og > 2COi) 2 Carbon has got reducing properties and thus acts as a reducing agent. Carbon reduces oxides of metals below it in the electrochemical and activity series to their respective metals, This occurs ‘on strong heating, and this reaction is used industrially for extraction of metals from their OFe8:PHO4,) + Ca) Phy + COjp, Fe:Ose + 3C > BFE) + ICO, LAO) + Cy) + Zn + CO)

• Sulphur vapours react with red hot carbon to give carbon disulphide. Cg + 2S) -* CSay
• Carbon dioxide is reduced by red hot carbon to carbon monoxide Cy + COxg) ~* 2CO: This

reaction is used in the industrial manufacture of producer gas.

Carbon Dioxide

Preparation ofa Dry Sample of Carbon Dioxide Gas in the Laboratory

Prepare a dry sample of carbon dicide gas in the laboratory Carbon dioxide is one of the oxides of carbon, The gas is present in the air at a level of approximately 0.03% by volume. It is also found dissolved in water. ‘The gas xs one of the by- products of all decaying organic matter. Without carbon dioxide there is no life on earth, It is used by all plants in the process of photosynthesis and both plants and animals evolve carbon

dioxide in respiration. Laboratory preparation of carbon dioxide ‘Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloride acid on marble (caleium carbonate) When dilute hydrochloric acid is poured on marble chips, effervescence occurs. Dilute hydrochloric acid reacts with the marble chips to give caleium chloride, water and carbon dioxide.

CaCO + AAChag) 7 CaCI) + H2Oy) + CO

The Properties of Carbon Dioxide

Analyse the properties of carbon dioxide Physical properties 1, Carbon dioxide is a colourless and odourless gas.

• Ih is denser than air.
• When the gas is cooled to 78°C, it tums straight into the solid (it sublimes). Sublimation is the

change of a gas straight into a solid or change of a solid straight into a gas. Solid carbon dioxide is called dry ice. It sublimes when itis heated or exposed to air.

• It has « melting point of -199°C and boiling point of -91.5°C,
• Carbon dioxide does not support combustion. This is why it is used in fire extinguishers

Chemical properties Reaction of carbon dioxide with lime water (Test for earbon dioxide) When a little carbon dioxide gas is bubbled into lime water (caleium hydroxide solution), the

solution tums milky. This is due fo the formation of @ white precipitate of insoluble caleium

carbonate Ca{OH)xas) + C02) + CaCO) * HO p This is @ confirmatory test for the presence of carbon dioxide. The test serves to distinguish carbon dioxide from any other gas. When excess carbon dioxide is bubbled into the lime water. the white perceptible dissolves to form a clear solution of soluble calcium hydrogen carbonate: CaCOs,) + HsO) + COay)—> CalHCO3)aixp Barium hydroxide ean also be used to test for carbon dioxide as it forms a precipitate of barium

carbonate: Ba(OH) a3) + CO2g) + BaCO%S) + 1209) Reaction of carbon dioxide with magnesium When a burning magnesium ribbon is lowered into a gas jar containing carbon dioxide gas, it continues to burn for a short time with a spluttering flame, A white ash of magnesium oxide and black specks of carbon are formed. The black specks of carbon can be seen on the sides of the sas jar, 2Mgbu)* COnjn > 2MBOy)* Cy This clearly shows that carbon dioxide contains carbon and oxygen

Reaction of earbon dioxide with water Carbon dioxide reacts with water to form a weak carbonic acid. When carbon dioxide is bubbled into water, it dissolves to form 2 weakly acidie solution of carbonic acid: H:0p) + COz) & HsCOsiay ‘The solution turns a blue litrmis paper pink. This indicates that the solution is slightly acidic and hence too weak to tum the blue litmus paper to red (as strong acids do). The solution has no

effect on red litmus paper

The Uses of Carbon Dioxide

Explain the uses of carbon dioxide

Uses of Carbon Dioxide include

• Fire extinguisher: Carbon dioxide is inert (ie. it does not burn) It is dense than air and does not

support combustion. Hence, it 1s a very useful fire-fighting chemical. When applied to fire, it forms a blanket over the burning material, Thus, it prevents air (oxygen) from reaching the burning material and therefore, extinguishing the flames,

• Manufacture of acrated (fizzy) drinks: Soda water and mineral water contain carbon dioxide

dissolved under pressure, Because the gas is only slightly soluble, it is bubbled into these drinks under pressure to make more of it dissolve. When the bottles are opened, the gas escapes and it

causes the “fizzy” Dissolved carbon dioxide is responsible for the pleasant taste of soft drinks

such as lemonade, Coca cola, Pepsi cola and other acrated drinks and mineral waters, Other beverages like beers are also bottled together with carbon dioxide.

• Refrigeration: Carbon dioxide is used for reffigeration purposes (ie. in the deep-Treezing of

foods). The gas liquefies at ordinary pressure to form dry ice witich sublimes at -78°C. Dry ive is a good refrigerant because it leaves no liquid after sublimation as is the case with ordinary ive 4 Manufacture of sodium carbonate by the Solvary Process:Carbon dioxide is used in the manufacture of anhydrous sodium carbonate in the Solvary Process. The sodium carbonate produced is used in the manufacture of glass,

• Manufacture of baking soda: Carbon dioxide is used in making baking soda (sodium

bicarbonate). Baking soda is prepared by passing carbon dioxide into cold concentrated sodium hydroxide solution: COsj+ 2NaOH) > NasCOsay + H0Further addition of carbon dioxide produces sodium bicarbonate which, at sufficiently high concentration, will precipitate ut of the solution as a solid: NasCOsju) + COzg + HsOq) + 2NaHCOs, Yeast and sodium bicarbonate (hydrogencarbonate) are important in the baking industry. Thus in beking of bread,

yeast is added to flour, sugar and water (forming the dough). In the making of cakes, baking powder (a mixture of bicarbonate and an acid) is used instead of yeast

• Rain making: When pieces of dry ice (solid carbon dioxide) are dropped into clouds, the

temperature of the clouds is lowered to such an extent that rain precipitates out.

• Photosynthesis: Plants use earbon dioxide from the air to manufacture their own food through

the process of photosynthesis