Chemistry Form One Notes – Air, Combustion, Rusting and Fire Fighting

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10. Layer separation technique is applied inthe recovery of liquids from contaminants

11. Solvent extraction process is applied in the extraction of certain edible ols from seeds, and in

the extraction of some metals from sludge mixture

AIR COMBUSTION, RUSTING AND FIRE

FIGHTING

101

Composition of air

Air is a mixture of different gases. The gases that make up the air include nitrogen, oxygen,

carbon dioxide, noble gases (argon, helium, neon, krypton and xenon) and a litle water vapour.

‘Air may also contain traces of impurities such a carbon monoxide (CO), sulphur dioxide (SO),

hydrogen sulphide (H;S) and other gases. The presence of these gases in air results in air

pollution. Table bellow shows the composition of air by volume. The proportion of wate vapour

‘The Gases Present in Air and their Proportions

The composition of air isnot exactly the same everywhere. It changes slightly from day to day

and from place to place. There is more water vapour inthe air on a damp day and in air above

‘more carbon dioxide. But the uneven heating of the earth’s surface bythe sun causes the arto

‘move continually, resulting in winds, The resultant winds spread the pollutants around

The percentage composition of air by volume

Gn Approximate percentage

Nawgen rar

Owes 21.00%

Noble ese ais agoa 090%

Carbon donde 003%

Water apour 09%

The Presence of Different Gases in Air

The determination ofr by mass was carted out by Dumas in 1841. The apparatus wed consists

of three units as shown bellow

E j heating furnace

aes (

potassium ‘concentrated J

gases. If we neglect the weight of carbon dioxide, the percentage of oxygen by mass (weight) in

dry, pure air is 23.2% and the remaining 76.8% is the percentage of nitrogen and rare gases.

‘The presence of nitrogen in air

by strongly heating magnesium inthe residual gas from the above experiment. Magnesium and

nitrogen will react thus:

Upon treatment with water, magnesium nitrite gives ammonia gas, The gas can be recognized by

its characteristic smell and its action of turning red litmus paper to blue.

3M gay + Noe)? MEN

The presence of oxygen in air

Oxygen is known as the ative portion of the air because it supports combustion and combines

with many other substances. Is presence and composition in air can be determined by using

these properties. Any of the following two (2) experiments ean be used to determine the

composition, by volume of oxygen contained in it

‘The Percentage of Oxygen in Air Experimentally

Determine the percentage of oxygen in ar experimentally

1. Experiment, Determination of the presence and proportion of oxygen in air by

combustion of a candle

Method

1. Placea smal candle on aplastic lid or any object that can float, Then setup the apparatus

produced by a burning candle

of cooling is to let the heated and expanded air to return to its normal condition. Then note the

108

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Determining the presence and percentage composition of oxygen in air by burning a candle

Observation and findings

The oxygen in air enclosed in the measuring eylinder is used to burn the candle to produce

carbon dioxide gas, The carbon dioxide so produced dissolves in sodium hydroxide solution. The

dissolved carbon dioxide causes the level of sodium hydroxide solution to rise up. The oxygen

21s used to burn the candle is practically equal tothe amount of carbon dioxide produced. This

faci, therefore, used o calculate the percentage of oxygen in ai

Model results

In the experiment, the inital volume ofr was found 1 be 705 em and the inal volume was 55

cm The percentage of oxygen in thea is calculated in two steps:

1. To find the volume of oxygen used up to burn the candle (which is practically equal tothe

volume of carbon dioxide produced and then absorbed by sodium hydroxide), we subtract the

final volume of ar fom the inital volume

Therefore, the volume of oxygen used for combustion ofthe candle = 14.7 em

=705 emi?) -5.0em>

=1470m?

Alteratively, the volume of oxygen used up canbe calculated by subtracting the inital volume

of sodium hydroxide solution fom the final volume, That is: Volume of oxygen used = final

10s

volume of sodium hydroxide ~ inital volume of sodium hydroxide = Volume of carbon dioxide

dissolved in sodium hydroxide.

2. The percentage composition of oxygen in the air=

[Volume of expen vse

Tata volume

= 87.100

705

= 208%

Therefore, the percentage of oxygen =

In practice, it is difficult to get an accurate result withthe above experiment.

Nolume of carbon dioxide dissolved in sodium hydroxide «100

Initial volume of calcium hydroxide

This is due to a number of reasons such as

1. Notall the carbon dioxide is absorbed by the sodium hydroxide

2. The candle may go out (stop burning) before all the oxygen is used up due to

accumulation of carbon dioxide in the cylinder.

3. The heating of the air inside the measuring cylinder causes the gases to expand. This is

‘why it is essential thatthe gases be allowed to cool to room temperature before reading the level

Experiment withcombustion of copper in airgives the more accurate results than the

combustion of the candle. The copper reacts with oxygen in the ar to give copper (ID) oxide.

2. Experiment. Determination of the presence and proportion of oxygen in air by the

combustion of copper in air

Method

1. Setup the apparatus as shown in figure bellow. Syringe A should contain 100 em of ar,

syringe B should be empty

108

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‘1. ‘The oxygen in the air reacts with copper to form copper(II)

teoumns

‘Volume after third heating and cooling = 79

The volume of oxygen used up = Initial volume of ir before cooling – volume of air aftr the last

heating and cooling,

= 100-79

=21

‘The presence of earbon dioxide in air

The percentage of oxygen in air = 21x 100

=21%

Carbon dioxide is present in air tothe extent of 0.03% by volume. The gas is formed during the

combustion ofall common fuels — wood, coal, coke, natural gas, petrol, diesel, paraffin oil, te,

all of which contain carbon,

Its breathed out as a waste product of respiration by all animals, All sorts of combustion and

bbuming produce carbon dioxide. The gas produced by all these processes accumulates in air

However, the amount of carbon dioxide in air remains constant instead of the tremendous

«quantities released into the atmosphere, This is because plants take up carbon dioxide. They then

convert it into complex starchy compounds during photosynthesis. The gas also dissolves in

‘ocean water and other water bodies.

Cut Oy +0025)

The presence of carbon dioxide in air can be shown by passing air through a test tube containing

some limewater (figure 6.5). After a time, the limewater turns milky. This shows the presence of

carbon dioxide

Te reaction involved is as follows:

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About 1% of the air by volume is made up of the noble gases. The most abundant of the noble

‘gases is argon. Others are neon, xenon, krypton and helium, The proportion of these four is very

‘minute, Argon and ncon are used in “gas-filled” electric light bulbs and coloured “neon”

clectrical signs. They are obtained ftom liquefied air

Air pollutants

‘The air always contains small quantities of many gases. Such gases include hydrogen sulphide,

sulphur dioxide, as well as dust and other solid particles, especially in industrial areas. These

‘gases are given off during the combustion of coal, and the fuels resulting from coal

SEPARATION OF AIR INTO ITS CONSTITUENT GASES

The air we breathe is necessary to keep us alive. It is also a chemical resource. Oxygen is used in

steel making, and nitrogen is used in making fertilizers. To use these gases in this way, they must

be separated from the atmospheric air. Air, as we studied in chapter 5, is a mixture of different

gases. The method used to separate its constituent gases is fractional distillation. The gases have

tobe liquefied so thatthe mixture can be fractionally distilled.

The process of separating the air into its constituent gases is difficult. It cannot be done in the

laboratory. Ii only done in industry. The chemical industry needs the gases from the ar in their

pure form.

‘The fractional distillation of air involves essentially two stages:

1, Fist, the air must be cooled until it tums int aliquid

2. Then, the liquid air is allowed to warm up again, The various gases bol off at different

temperatures

Stage 1: Liquefaction of air

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Combustion

‘The Concept of Combustion

chemilly with the bring sane to produce anew sbsance, ot we thal ee

Combustion of a substance involves its reaction with oxygen and the release of energy. These

reactions are exothermic and often produce a flame. An exothermic reaction isthe one that is

accompanied by release of heat tothe surrounding environment. Combustion in which a flame is

produced is described as burning. During burning energy is given out in the form of heat, light

and sound,

‘The Combustion of Different Substances in Air and Analyse the Products

Demonstrate the combustion of different substances in air and analyse the products

Many diferent substances bum in air to produce different products. Here are examples of

‘combustion of some common substances:

Sulphur

This is a yellow powder. When burnt in ar, it gives misty fumes of sulphur dioxide gas.

‘Sulphur powder + air (oxygen) + sulphur dioxide gas

S(s) + Og) + SOXa)

Copper

‘When a piece of copper foil in pair of tongs is held in a Bunsen flame, it becomes red-hot. On

cooling, a black layer of some substance is observed. This black substance is copper oxide. The

reaction occurs thus:

Cooper + air (axygen) = Copper axide

2Culs) + Og) F2Cu0Ks)

Magnesium

‘When one end ofa piece of magnesium ribbon in tongs is placed in a Bunsen flame, it burs with

1 dazzling flame leaving a white ash. This white ash is magnesium oxide,

Mg{s) + 04g) + 2Mgo(s}

Hydrocarbons

Candle wax is @ hydrocarbon. When it bums in air, the carbon and hydrogen ofthe wax react

with the oxygen of the arto give carbon dioxide and water vapour respectively

Cs)+ 048) -+ COW)

2H.(g)+ 0.68) + 2H.0@)

‘These are substances containing carbon and hydrogen only. The burning of these organic

substances produces carbon dioxide and water vapour a the main products. If oxygen supply is

low, combustion is incomplete and carbon monoxide may be formed,

Coat

Coal is a slid fue that will urn in ar to give the following products:

Coal + ash + soot smoke + gases (carbon dioxide and

‘The Application of Combustion in Real Life

Describe the application of combustion in real life

1. The combustion of a natural gas isan important source of energy for homes and industry

Natural gas is mainly methane. is complete combustion produces carbon dioxide and water

vapour

CHAg)+ 048) + CO(g)+H.0(@)

Substances like methane, which undergo combustion readily and give out large amount of

2. There are some reactions where fuels and other substances bur to produce aflame. These are

evident. The most important of these isthe crucial biochemical reaction that releases energy in

cour body cells called cellular respiration.

Our bodies need eneray 19 make possible the reactions that take place in our cells. These

reactions allow us to carty out our everyday activities. We need energy to stay alive, We get this

nergy from food. During digestion, food is broken down into simpler substances. For example,

the carbohydrates in ree, potatoes and bread are broken down to form glucose. The combustion

of glucose with oxygen inthe cells of our body provides energy.

Glucose + oxygen => carbon dioxide + water + energy

C.H,.04aq) +6048) + COs) + 084,00)

The reaction is exothermic nd is known as cellular respiration.

3. We combust fuels to heat homes and keep ourselves warm, cook our food, and even burn

4. Combustion of fuels in automobile engines produces power (energy). This energy is supplied

to different parts of motor vehicles to make them move from one point to another oF carry out

some crucial activities such as grinding, pumping, hauling ete. The operation of such machines

could be impossible without combustion of fuel that produces energy to make them work

‘5. Combustion of ful in different bumers produces heat and light used for different purposes in

a chemistry laboratory

6. Extraction of metals: Moderately reactive metals such as zinc, iron and lead are roasted in a

special furnace (kiln) to form oxides. The resulting oxides are then reduced with carbon to get

the pure metal. This process of extracting a metal fom its ore by heating is called smelting

7. In metallurgical industry, combustion is used during welding, Welding is the process of

joining metas by melting the parts and then using a filler to form a joint It can be done using

diferent encrgy sources, including gas lame,

Fire fighting

Firefighting isthe act of extinguishing destructive fires. A fire fighter fight these fires to prevent

destruction of life, property and the environment. Firefighting is highly technical profession

that requires traning and education in order to become proficient.

Types of Fires According to their Causes

Classify types of fires according to their causes

Before starting to fight the fire itis important to know the size and type ofthe fire that you are

ning to put off. The kind of firefighting material you are going to use will also depend on the

‘ype ffir in question. Fires are classified based onthe type of burning materials.

1. Class A fires

These are the fires in which the burning materials are ordinary combustible materials such as

paper, wood, cardboard, coal, rubber, clothing, fumiture and most plastics. Water isthe best

extinguisher fr these fires. However, any other type of extinguisher, except carbon dioxide, may

be used

2. Class B fires

These fires involve ammable liquids such as peo, kerosene, oil alcohol, the, vanishes, et.

Fo small fires fire blanket or sand may be use. Ifthe fire is large, use foam, dry powder or

carbon dioxide extinguisher. Water should not be used on clas B fires because the burning

smatra, being lighter than water, will just lot and spread the fire fuer.

3. Class C fires

The burning material involves flammable gases e.g. hydrogen, acetylene, coal ga, butane,

aethane, propane, etc. The best extinguishers to use in Fighing against these fires are foam, dry

powder or carbon dioxide extinguishers. It is important to tum off the gas supply, and spray

water on the gas tank to cool it down

4. Class D fires

‘The burning material sa metal. Alkali metals such as sodium or potassium may catch fie when

they come in contact with water and oxygen. At high temperatures, many metals react with

cnygen vigorously. Fites that involve burning meals should not be extinguished by water, This

is because the burning metal can react with water to give hydrogen (another potential ful). The

appropriate extinguisher to use is foam or dry powder extinguisher

5. Class E fires

‘These fires involve electrical equipment such as appliances, wiring, circuit breakers and outlets

‘You may use carbon dioxide or dry powder extinguisher to put off these fires. Never use water as

itcan conduct electricity and give an electric shock, Also remember to switch off power from the

6. Class F fires

The burning material is cooking ol o fat. A cooking oil fre i the kitchen can be extinguished

by covering the pan with a fire blanket or damp cloth. Foam, dry powder or carbon dioxide

extinguishers also work by cutting off the air supply to the fire. For large fires, wet chemical

extinguishers are recommended.

Different Types of Fire Extinguishers used to Extinguish Different Types of

Fire

“deni diferent types of fre extinguishers used extinguish diferent pes offre

Before choosing the best fire extinguishers for fighting different types of fires itis crucial to

‘entity the typeof buing materials rst, and hence the ype of fire such as

(Class A: Solids such as paper, wood, clothing, rubber, ste

Class B: Flammable liquid suchas parafin, petro, ol spirit, alcohol, te.

(Class C: Flammable gases such as propane, butane, methane, hydrogen, et

(Class D: Metals such a aluminium, magnesium, titanium, ete

(Class E: Fires involving electrical equipment such as appliances, circuit breakers and outlets,

‘Types of fire extinguisher to use for each type of fire

Water extinguisher

This isthe cheapest and most widely used fire extinguisher. Iti used for class A fires. I is not

suitable for class B (liquid) fires, or where electricity is involved

Foam extinguisher

This is more expensive than water extinguisher, but more versatile. It is used for classes A and B

fires, Foam spray extinguishers are not recommended for fires involving electricity, but are safer

than water if mistakenly sprayed onto live electrical apparatus.

Dry powder extinguisher

This is often termed as “multi-purpose” extinguisher, as it can be used on classes A, B and C

fies, It isthe best for liquid fires (class B). It will also efficiently extinguish class C (gas) fires.

However, take eare because it ean be dangerous to extinguish a gas fire without first isolating the

‘2 supply. Special powders are available for clas D fires.

‘When powder-type extinguishers are used indoors, the powder can obscure vision or damage

‘goods and machinery. Its also very messy

Carbon dioxide extinguisher

Carbon dioxide is ideal for fires involving electrical apparatus (class E), It will also extinguish

class B (liquid) fires. However, the extinguisher has no post-fire security and the fire could re-

ignite

‘Wet chemical extinguisher

‘This is a special extinguisher for class F fires. The extinguisher contains potassium salts, The

salts not only help to cool down the flames but also form a ‘saponification’ blanket that

effectively smothers the flames with thick, soapy foam,

Specialist ponder extinguisher

This isa specialist fie extinguisher for use on class D fires (fires on combustible metals such as

sodium, potassium, magnesium, lithium, titanium, manganese and aluminium), especially in the

form of powder or turnings,

‘The Components Needed to Start a Fire

Stare the components needed to start a fire

To extinguish fre, it i ocesary to remove one of more ofthe three components of combustion.

Any fire nossa fuel, oxygen (ait) and heat to kesp it going, Remove any one of them and the

fre will go ou. These components are as shown inthe fre triangle below

omen WA \ sen

// Sito

The fire rangle

‘fire will contin or start to bur i these component are present

(0) Fac: This refers o ny combustible material be it sold, guid oF gaseous material provided

itcan catch fire and burn. You can stop fre by removing the combustible materia rom the path

of re

(i) Oxygen (ar): Onyzen supports combustion. A fuel will only burn if there is sufcient

supply of oxygen. You can extinguish Fire by displacing or taking away oxygen supply from the

fre or by blocking the s33 supply to the fire

(i) Heat: The temperature shouldbe atthe kindling pont of that fel or above it Every Fel has

its own kindling point Below the kindling point, the fue wll not catch fire. You can put out fe

ty lowering the temperature below the kindling point ofa particular ful, Water may be wsed to

cooldown the fel. The vaporization of wate absorbs the hati cools the smoke, at, wall

objects etc, which could be used as further fel

Fire Extinguishers According to the Chemicals they Contain

Cassi fire extinguishers according tothe chemicals they contain

Fire extinguishers are classified according tothe typeof chemicals they contain

1. Liquid carbon dioxide extinguisher

This extinguisher contains liquid carbon dioxide. The liquid is contained in a metal container.

‘When the safety pin is removed, carbon dioxide evaporates as solid “snow (carbon dioxide

sublimes). The snow settles onthe fire and suffocates it

2. Soda-acid extinguisher

This extinguisher has a metal case containing soda (aqueous sodium carbonate or sodium

hhydrogen carbonate). In the metal case there is a glass botle containing a concentrated acid

(sulphuric or hydrochloric acid), Ther is a knob attached tothe top of a metal case. Hitting this

nob breaks the acid bottle thus bringing the acid and the soda into contact. The two react to give

carbon dioxide, eg

NaHCO,u)#HCIa) + COsy)+NECl ay + HO 0

The gas forms bubbles withthe solution, thereby forming foam which is forced out ofa et ofthe

case. The foam is directed to the fre where it covers the buring liquid, excloding all ai fom

Some extinguishers are made in such a way that turning them upside down brings the soda and

acid into contact andthe reaction proceeds as stated above

120

Chemical composition of

Type agent ‘Suitable for Unsuitable for

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(@) strike the knob (b) tum upside down

3. Foam extinguishers

This is diferent from the soda-acid type in that it contains sodium hydrogen carbonate inthe

tal case, bu instead ofthe concentrated ac, it contains aluminium sulphate and saponium in

the glass bottle. On mixing the tree components, carbon dioxide gas is produced. The gas is

ejected out as foam, The foam here lass longer than the foam in the soda-acid extinguisher. The

foam so produced also keeps air away from the burning materi

4. Dry chemical extinguisher

This extinguisher uses powdered sodium hydrogen carbonate and nitrogen gas kept at high

pressure. When the gas cartridge is broken using the top cap the carbon dioxide under pressure

Propels the powder. The powder forms layer over the burning material to kep ar away,

Table bellow summarizes the types of fire extinguishers, indicating the chemicals they contain

andthe classes of fire the ae suitable or unsuitable fo.

Table: Types fire extinguishers and the chemical composition of heir extinguishing agents

APW (Ai Ondinry ap water ‘lass B,C, and (vill pea the ame and make

pressurized ae) presi witha Clas the fe igs)

Fine sodium bierbonate Class D- Aira and eleonis cursive to meals

oder prsnuind wi | Class A, B, | such aaniionote: ‘Though iti safe owe indoor

Dy chomizalDC) nitrogen CantE ean obscure vison

Nonflammsble —cubon

dioxide gas under eteme | Class B,C Class A (eaves 4 flammable substance oo. the

co. reste and extinguished materi which cnet er)

Iromechlowdilure- Class A and

Halon methane E tas Band C(t suitable

Class A and

Foun Procisand Muow-potias 8 cust

WetchemicaWC)_Poussiumseeae CasF Cas

Clas A, | Beenie equipment (eve a icky resid that may

Monoammosim ptosate Clase B and be damaging 10 clectical appliances sich at 8

nc wit antopencanie | C compute)

Ponders of NaCl Cu or

Specialist powder graphite under extreme

6 reste Clas Class A,B,C, EandF

Precautions on using fire extinguishers

The following are some safety precautions you have 0 keep in mind when using fire

extinguisher:

Extinguishing Small Fires Using the Right Types of Fire Extinguishers

Rusting

The Concept of Rusting

money All ffs mist be made to tp ir ose! tems fom sting. This can be achieved if

we know te conditions necessary for iron to rst

‘The Conditions Necessary for Iron to Rust

Demonstrate the conditions necessary for iron 0 rast.

When ton sl in contact with bth water and oxygen (or i) teats to form hydrated iron

{ty oxide. hon will not rust on exposure to dy ato ai-froe water (wate that has ben boiled

to expel all disolved ir) ony. However, ron will easly and realy rust in water that has

dissolved air init In igre 68, only the ron mail that is in contact with both water and ir sts

Therefore, rusting wil only occur inte presence of both water and oxygen. If ne of the two

conditions is exchded in one way or another, sting will nt ake place tal

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Findings

Nails in tube | will rst Nailin tubes 2and3 will ot ust

Reasoas

In tube 1, nails ae in contact with both water and air (oxygen, In tbe 2 the water has been

toiled to expel the dissolved sir, In addon, any ar above the water is prevented fom

cisotving in Died water by «lye of cil So, the mals are completely shicded away from i

Therefore, rstng is imposible. in tube 3, mils are in cont with ir only. The moisture

present in ai is absorbed by anhydrous calcium chloride. Any moisture that might have been

absorbed by the anhydrous calcium chloride is prevented from reaching the nails by a tuft of

cotton wool. The cotton woo! also absorbs some moisture directly from the air. Therefore, tube 3

will always carry dry air (moisture-fee air). Hence, no rusting of iron nails occurs.

This experiment demonstrates the fact that for ito to rust, both water and air (oxygen) must be

present. If one of these conditions is controlled, no rusting can take place

Similarity between rusting and burning

Chemically, rusting and burning are similar processes in that they both require oxygen. Consider

the burning of magnesium to give magnesium oxide.

2Mg(s) + Og) — 2MgO(s)

In this process, magnesium combines with the oxygen ofthe air to form magnesium oxide

During rusting, iron combines with oxygen of the ai inthe presence of water to form brown

hydrated iron(II) oxide, “ust”

AF e{s) + 304g) + 201.0 — 2Fe.0,.0H.0(8)

In addition, the two processes, burning and rusting, are exactly similar in that they both generate

heat. The only difference isin the time required for each of the two processes to take place.

During rusting heat is given out, but without being noticed because of its slower rate of

production. Burning produces noticeable heat and light.

‘The Different Methods of Preventing Iron from Rustin

Describe the different methods of preventing iron from rusting

We have learned that for iron to rust there must be direct contact between the iron and both water

and oxygen ffom the air. Therefore, in order to stop rusting we must protect iron from either

‘ater (moisture) or oxygen (at) or both. The following are some of the methods used to prevent

iron from rusting:

Painting

1ethod is widespread for objets ranging in size fom ships and bridges to garden gates. Paints

that contain lead or zinc are mostly used. These paints ae especially good for preventing rusting

For example, red lead” paints contin an oxide of lead,

‘As onygen and water cannot reach the iron, it does not rst, However, if the pint layer is

scratched off rusting may occur So, regular repainting is necessary to keep this protection ntact.

Oiling and greasing

The oiling and/or greasing ofthe moving pars of machinery forms a protective fil, preventing

rusting, Moving parts cannot be painted since the paint layer can be easily seratched off during

‘movement. Again, the teatment must be repeated to continue the protection,

Plastic coating

Stel is coated with plastic for use in garden chairs, refrigerators, bicycle baskets, dish racks, ee

The plastic PVC (polyvinyl chloride), a trade name for polychloroethene, is often used for this

purpose. Plastic is cheap and can be made to lok atrative

Electroplating

Electroplating isthe coating of one metal with a layer of another metal by means of electrolysis

‘where the metal tobe coated isthe cathode and the coating metal he anode.

{An iron or steel objet can be electroplated with layer of chromium or tin to protect against

rusting. A ‘tin can’ is made of ste! coated on both sides with a fine layer of tin, Tin is used

because itis unreactive and non-toxic, However, if protective layer is broken, then the stel

beneath wil begin to rust. So, proper handling of tinplate items is neded.

Galvanizing

The zine layer can be applied by several different methods, These inclde electroplating or

dipping the object nto molten zinc. When anion or steel article i dipped into molten zine and

Sacrificial protection

zine or magnesium are attached tothe bul ofa see! ship ool ig, it comodes in preference to

the iron. When the blocks are nearly eaten away, they can be replaced by fesh blocks

Underground gas and water pipes ae connected by wire to blocks of magnesium to obtain the

meres to prevent rasting of the whole bul

\ JR ate

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Blocks of zine or magnesium) atached to the hull ofa ship

Alloying

Alloys are mixtures of metals. For example, ron can be mixed with small quantities of much ess

reactive metals to form an allo called stainless steel, Stainless stot contins ion mixed with

clomium, nickel and manganese. Sunless steel does not rust. It also has a very atactive

appearance, Its used to make cutlery and kitchen equipment.

Use of silica gel

Silica is a common name for silicon dioxide (Si). Silica gel i a granular, vitreous, highly

porous form of silica made syntetcally from sodium silicate. Despite its name, silica gel i a

soli, Itis used as a desiccant, which absorbs moisture to prevent rusting of ion items or atcles.

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