NTA Level 4 • Semester 2 • PST04210

Acids, Bases, Salts, Dissociation, Buffers and Periodic Table

Pharmaceutical Inorganic Chemistry • Source Session/Topic 2

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PST 04210: PHARMACEUTICAL INORGANIC

CHEMISTRY

REVIEW QUESTIONS

VOLUME 02: Acid, Base, Salt, Degree Of Dissociation,

Buffer Solution, Importance Of Chemistry In Pharmacy,

Arrangement Of Elements In The Periodic Table.

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1. Give the definition of acid with reference of the following.

i. Arrhenius definition of acid

A substance that produce H+ only as a positively charged ion

Example HCL, HBr, H2SO4

This definition applies only in aqueous media (water)

ii. Lewis definition of acid

Any species capable of accepting a pair of electrons (electron acceptor).

Examples: H+, and metal cations, molecules such as BF3 with incomplete octets, and

ones such as SiF4 where octet expansion is possible

iii. Brønsted definition of Acid

A proton donor

2. List two (2) classes of acids with an example on each.

i. Strong acid

The acid that ionizes completely

Example HCl, H2SO4 and HNO3

ii. Weak acid

The acid that ionizes partially

Example CH3COOH

3. Outline four (4) distinctive properties of an acid.

i. Acids taste sour

ii. Aqueous solutions of all Arrhenius acids contain hydrogen ions

iii. Acids have a pH of less than 7

iv. Acids turn phenolphthalein COLOURLESS and litmus RED

4. List seven (7) physical properties of acid.

i. Acids taste sour

ii. Acids have a pH of less than 7

iii. Acids are harmful to living cells

iv. Aqueous solutions of all acids contain hydrogen ions

v. Acid turns blue litmus red

vi. Strong acids are corrosive

vii. Aqueous acid solutions conduct electricity

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5. Enumerate three (3) chemical properties of acids.

i. Metals above copper in the reactivity series react with acids, giving off hydrogen gas,

forming a salt

ii. Reacts with bases to form salts (neutralization reaction)

iii. Reacts with metal carbonates to produce salt, water and carbon dioxide gas

(effervescence is observed)

6. Outline seven (7) importance of acid in pharmacy.

i. Preparation of analgesics

ii. Improve solubility of drugs

iii. Preparation of skin remedies as keratolytic (soften the outer layer of skin)

iv. Used as reagents for analytical procedures

v. As buffer systems to maintain the pH of a medicinal agent at an optimal value

vi. Preparation of effervescent mixtures (a medicinal dosage form sometimes used to

render a medicinal more palatable for oral administration)

vii. Preparation of germicides

7. Give the definition of base with reference of the following.

i. Arrhenius base

Base is a substance that produce OH- only as a negatively charged ion

Example NaOH, Mg(OH)2

This definition applies only in aqueous media (water)

ii. Lewis base

Base is any species with a pair of non-bonding electrons available for donation

(electron donor)

Examples molecules such as NH3, and anions such as F-

iii. Brønsted Base

A proton acceptor

8. List two (2) classes of bases with an example on each.

i. Strong Base

The base that ionize completely

Examples NaOH and KOH

ii. Weak Base

The base that ionize partially

Examples NH3

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9. Outline six (6) distinctive properties of a base.

i. Bases have a pH of more than 7

ii. Dilute solutions of bases taste bitter

iii. Bases turn phenolphthalein PINK and litmus BLUE

iv. Aqueous solutions of all Arrhenius alkalis contain hydroxide ion

v. Soapy touch

vi. Bases react with fats to form soap and glycerol (saponification)

10. State six (6) physical properties of bases

i. Bases have a pH of more than 7

ii. Dilute solutions of bases taste bitter

iii. Bases turn phenolphthalein PINK and litmus BLUE

iv. Aqueous solutions of all alkalis contain hydroxide ion

v. Bases feel slippery; for example, soaps, which contain bases

vi. Aqueous base solutions conduct electricity

11. List four (4) Chemical Properties of Bases

i. Bases react with fats to form soap and glycerol (saponification)

ii. Reacts with acids to form salts (neutralization reaction)

iii. React with Ammonium salts to produce ammonia detected by its pungent odour

(strong smell) and by turning damp red litmus blue

iv. Alkali's are used to produce the insoluble hydroxide precipitates of many metal ions

from their soluble salt solutions.

12. Outline four (4) importance of bases in pharmacy.

i. Improve solubility of drugs

ii. Preparation of effervescent mixtures

iii. Development of gastric antacids

iv. As systemic alkalizers and acidifiers

13. Define the term salt.

A compound that results from the neutralization reaction of an acid and a base

Composed of related number of cations (positively charged ions) and anions (negatively

charged ions) to make an electrically neutral product.

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14. Outline three (3) categories of salt with an example on each category.

i. Normal Salts

• Normal salts are formed when all the replaceable hydrogen ions in the acid have

been completely replaced by metallic ions

• Normal salts are neutral to litmus paper

• Example NaCl and ZnSO4

• Acidic salt

ii. Acidic salts are formed when replaceable hydrogen ions in acids are only partially

replaced by a metal

• Acid salts are produced only by acids containing more than one replaceable

hydrogen ion

• An acid salt will turn blue litmus red

• In the presence of excess metallic ions an acid salt will be converted into a normal

salt as its replaceable hydrogen ions become replaced

• Example NaH2PO4, Na2HPO and KHSO4

iii. Basic salt

• Basic salts contain the hydroxide ion, OH-

• They are formed when there is insufficient supply of acid for the complete

neutralization of the base

• A basic salt will turn red litmus blue and will react with excess acid to form

normal salt

• Example Zn(OH)Cl and Mg(OH)NO3

15. Describe six general properties of salts.

i. Nearly all ionic compounds are crystalline solids at room temperature

ii. Better solubility and dissolution rates

iii. Conduct electricity when molten or dissolved in water

iv. Have an overall net charge

v. Higher melting and boiling points compared to other types of compounds (covalent

compounds)

vi. Hard and brittle because their ions are arranged into unit cells which form layers.

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16. Outline seven uses of salt.

i. Preparation of Oral Rehydration Salts (ORS)

ii. Preparation of mineral supplements.

iii. Preparation of germicides

iv. Preparation of astringents

v. Preparation of skin protectives

vi. Preparation of anticonvulsants

17. Differentiate between dissociation and degree of dissociation.

• Dissociation

Refers to the process by which compounds separate or split into smaller particles such as

atoms, ions or radicals

• Degree of dissociation

Refers to the fraction of acid molecules that dissociate compared with the initial

concentration of the acid

The amount of solute dissociated into ions or radicals per mole

Very strong acid and bases has a degree of dissociation close to 1

Weak acids and bases have a degree of dissociation less than that of the strong acids and

bases.

18. Explain the importance of degree of dissociation.

• It indicates the strength of acid

Using the degree of dissociation of a particular acid/base it is easier to predict its strength

and thus help in studying the properties of pharmaceutical ingredients such as solubility,

stability, activity, and absorption

19. Define the following terms.

i. Buffer solution

Refers to a solution that changes pH only slightly when small amounts of a strong

acid or a strong base is added.

ii. Buffer capacity.

The ability to resist the change in pH after addition of a strong acid or strong base.

The amount of strong acid (e.g. HCl) or strong base (e.g. NaOH) in moles that can be

added to one liter of buffer in order to change the pH of the buffer by one unit

20. List two (2) types of buffer solution.

i. Acidic buffer solution

ii. Basic buffer solution

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21. Outline three (3) main buffer systems that maintains the pH of blood plasma at 7.4.

i. Hydrogen carbonate /carbonic acid buffer: Dissolved carbon dioxide, which gives

carbonic acid (H2CO3) in solution, and its sodium salt (usually sodium bicarbonate,

NaHCO3).It maintains the pH of the blood plasma at a constant value of 7.35 – 7.45

ii. Phosphate buffer have an intracellular role Dihydrogenphosphate (H2PO4 -), with its

sodium salt

iii. Protein buffer

22. State two (2) components of a buffer system.

i. weak acid or weak base

ii. Its salt (conjugate base) or (conjugate acid)

23. List two (2) general features of a buffer solution.

i. Contains a weak acid with its salt (conjugate base) or a weak base with its salt

(conjugate acid)

ii. Resistant to pH change in pH

24. Describe nine (9) features of a protein buffer system.

i. Proteins are polymers composed of repeating units called amino acids containing

NH2 and COOH groups in the same molecule

ii. Proteins are composed of about 20 different amino acids, which are connected to each

other by peptide bonds formed between one amino acid and its neighbour

iii. The side-chain of the amino acid may be acidic (as in the case of glutamic and

aspartic acids), basic (as in the case of arginine and lysine) or neutral (as in alanine)

iv. Amino acids are amphoteric (capable of acting as both acids and bases)

v. Most proteins act as weak acids and form buffers with their sodium salts

vi. These internal salts form zwitterion (dipolar ion), and formation of the zwitterion

makes the amino acid very polar and therefore very soluble in water

vii. If acid is added to the zwitterion, the ionised COO- group will accept a proton to give

un dissociated COOH and the overall charge on the amino acid will be positive, due

to the NH+

viii. If base is added to the zwitterion, the NH3+ (which is really the conjugate acid of

NH2) will function as an acid and donate its proton to the base the overall charge on

the amino acid will be negative, due to the ionised COO-

ix. Amino acids are ionised at all values of pH, positively charged at low pH, negatively

charged at high pH and zwitterionic at neutral pH

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25. Outline two (2) uses of buffer solution.

i. Maintain the pH of a medicinal agent at an optimal value.

Bronsted acids and bases have been used to maintain and adjust the pH of body

fluids.

ii. Improve solubility of drugs

Create and maintain pH conditions in a system that cause the drug to be in its ionized

state

Ionized fraction of a drug is much more soluble in water due to its increased polarity

relative to the un-ionized fraction

26. Explain the importance of chemistry in pharmacy.

i. Exploration of suitable sources of drugs

ii. Exploration of the chemical and the physical properties of drug

iii. Determination of storage conditions

iv. Determination of packaging material

v. Choice of the appropriate route of administration

vi. Study of the biopharmaceutical parameters (absorption, distribution, metabolism and

vii. Diagnosis and treatment of diseases

27. Explain how chemistry can be used in diagnosis and treatment of diseases.

• Medicines or drugs that are taken for the treatment of various ailments are chemicals

• Various elements are used for diagnosis (diagnostic radiopharmaceuticals) example

Technetium-99m (99Tc) a common radioisotope used in imaging of various body

organs.

• Various radioactive elements are involved in treatment of various disorder

(therapeutic radiopharmaceuticals) example Sodium iodide 131 (131I) used for

treatment of thyroid cancer

28. State how chemistry can be used in the following practices.

i. Determination of storage conditions

• Chemistry is important in the exploration of suitable storage condition

• Example: Drugs with an ester functionality, such as aspirin, could be quite

unstable in the presence of moisture, and should be kept in a dry and cool place

ii. Determination of packaging material

• The concept of chemistry is needed in the choice of packaging

• Example amber colored bottle is chosen for drugs which are sensitive to light

iii. Choice of the appropriate route of administration

• When administered, the action of a drug inside the body depends on its binding to

the appropriate receptor, and its subsequent metabolic processes, all of which

involve complex enzyme driven biochemical reactions

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29. Describe the significance of chemistry in the following aspects.

i. Exploration of suitable sources of drugs

• Chemistry is involved in all processes of the discovery phase

• Sources of drug molecules can be natural example narcotic analgesic, morphine,

from Papaversomniferum (Poppy plant), synthetic, example a popular analgesic

and antipyretic, paracetamol, or semi-synthetic, example semi-synthetic

penicillins

• If a drug molecule has to be purified from a natural source such as a plant,

processes such as extraction, isolation and identification are used, and all these

processes involve chemistry

ii. Exploration of the chemical and the physical properties of drug

• In the pre-formulation and formulation studies of the drug, chemistry is required

in the determination of structures and the physical properties such as solubility

and pH, of the drug molecules

• Each type of dosage form to be designed requires careful study of the physical

and chemical properties of drug substances to achieve a stable and efficacious

product

30. Describe the arrangement of elements in the periodic table.

i. Periodic table

• Refers to a table in which elements are arranged by the order of increasing

atomic number.

ii. Periodic law

• States that “the properties of the elements are a periodic function of their

atomic weights”

• Developed by Dmitri Ivanovitch Mendeléev

iii. Atoms are arranged in the order of increasing atomic number

• Atomic number refers to the number of protons in the nucleus of an atom

iv. The vertical columns of the table are called groups or families

• Numbered from 1 to 18

• Elements in the same group have the same number of outer shell electrons,

and hence similar chemical properties

v. The horizontal rows of the table are called periods

• Numbered from 1 to 7

• Elements in the same period have electrons in the same outer shell

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31. Explain the physical trends of the periodic table.

• Core Charge

o Refers to the attraction that an outer shell electron feels towards the nucleus

o Down the group it is constant

 There is always equal number of electron in the outer shell example in the

alkaline metals there is always one electron in the outer shell.

o Across a period it increases

 There are more electrons in the outer shell which are greatly attracted to the

nucleus

• Atomic radius or size

o Refers to the diameter of an atom

 One-half the distance between the two nuclei in two adjacent metal atoms

 For elements that exist as simple diatomic molecules, the atomic radius is one-

half the distance between the nuclei of the two atoms in a particular molecule.

o Down the group it increases

 There is an increase in the number of shells

o Across the period it decreases

 There is an increase in core charge, the outer shell electrons are attracted

closer to the nucleus (it’s the same shell but there are more electrons in the

shell as you move across the period)

• Ionisation Energy

o Refers to the minimum amount of energy required to remove the highest energy

electron from an atom (energy to steal an electron)

o The minimum energy (in kJ/mol) required to remove an electron from a gaseous

atom in its ground state.

o Down the group it decreases

 The size of the atom is increasing, the attraction is weaker between the outer

shell electrons and the nucleus therefore electrons are easier to remove

o Across a period it increases

 There is an increase in core charge, the attraction is greater between the outer

shell electrons and the nucleus. Therefore electrons are harder to remove

• Electro negativity

o Refers to measure of the ability of an atom to attract an electron towards itself.

(love of electrons)

o Down the group it decreases

 The electrons are further from the nucleus, there is a weaker attraction

o Across a period it increases

 There is an increase in core charge, there is a greater attraction of the outer

shell electrons to the nucleus

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32. A). Define diagonal relationship.

Refers to similarities between pairs of elements in different groups and periods of the

periodic table. Specifically, the first three members of the second period (Li, Be, and B)

exhibit many similarities to those elements located diagonally below them in the periodic

table.

B). List three (3) pairs of elements that exhibit diagonal relationship,

i. Lithium and Magnesium

ii. Beryllium and Aluminium

iii. Boron and Silicon

C). State the reason for pairs of elements to exhibit diagonal relationships.

The reason for this is the closeness of the charge densities of their cations

• Charge density is the charge of an ion divided by its volume

• Cations with comparable charge densities react similarly with anions and

therefore form the same type of compounds

• The chemistry of lithium resembles that of magnesium in some ways; the same

holds for beryllium and aluminium and for boron and silicon

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