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10
Viva Voce in
Pharmaceutical Chemistry
Q 63 Enumerate the different parts of analytical balance.
Ans: Leveling screw, knob or key, base, wooden case, pointer
and pointer scale, pans, pillar, graduated beam, adjusting
screws, sliding rod for rider are different parts of analytical
balance.
Q 64 Write the rules of weighing.
Ans:
1. The balance should be placed on a firm platform.
2. Sit squarely in front of balance while weighing.
3. Place calcined calcium chloride in the back corners of the case
to absorb the moisture.
4. The balance and the pans should be clean.
5. Align the balance strictly vertical by its plumbline.
6. While weighing, use only side doors of the case, do not raise
its front door.
7. The object to be weighed is placed on left-hand pan while the
weights on the centre of right hand pan.
8. The chemical to be weighed should be placed and weighed
in a weighing bottle or over a watch glass. Never place the
chemical directly on the pan or on paper.
9. Ensure that objects being weighed have attained the room
temperature. This can be achieved by keeping the chemical
near the balance for 30 mins before weighing.
10. While weighing, change the load on the balance only after
fully resting it.
11. All the weights should be handled with forceps and not with
fingers.
12. While observing pointer deflections, keep the case doors shut.
13. Never load the balance above its maximum load (200 g).
14. Before and after using, keep the rider on the carrier hook.
15. When the weighing is completed, remove the chemical and
weights from the pans.
16. Any spilled material on the pan or case should be immediately
cleaned with a soft brush. Wipe the pans with chamois leather.
Q 65 How can 5 mg samples be weighed on analytical balance?
Ans: The rider is placed at marking 5 on the right hand side of the
beam scale, the effect is equal to 0.005 g weight or 5 mg weight
placed on the right hand pan of balance. Now, weigh the chemi-
cal on left side pan. The weighed chemical would be 5 mg.
General Questions 11
Q 66 What is the use of a rider?
Ans: Rider is the piece of suitable wire appropriately shaped to
ride on the beam of balance. The rider is used to weigh the
quantities between 1 and 10 mg.
Q 67 What is the weight of rider?
Ans: The commonly used rider weighs 10 mg, when the beam is
graduated to 10 divisions to the right side of zero and 10
divisions to the left side of zero.
Q 68 How the weighing beam is graduated and what each major
division and subdivision indicate?
Ans: The central division is zero. On the right hand side and left
hand side there are 10 divisions. Each major division indicates
the weight of 0.001 g or 1 mg.
In between two major divisions, there are 5 subdivisions. Each
minor subdivision indicates 0.2 mg. So, if the rider is placed
on 4th subdivision between the markings 7 and 8, the weight
is 0.0078 g or 7.8 mg.
Q 69 What do you understand by fractional weight box?
Ans: Weights smaller than 1g are called fractional weights or
miligram weights. They are leaf-shaped foils of aluminium
with one of the sides turned up for picking with forceps. The
fractional weight set has 500, 200(2), 100, 50, 20(2), 10, 5, 2(2)
and 1 mg weights.
Q 70 Would you use fractional weights for weighing quantities
less than 10 mg?
Ans: Rider is preferred for weighing correct quantities between 1
and 10 mg.
Q 71 Write the maximum and minimum load weighed on
analytical balance.
Ans: Maximum weighable load—200 g
Minimum weighable load—1 mg
12
Viva Voce in
Pharmaceutical Chemistry
Q 72 How would you weigh hygroscopic, volatile and liquid
substances using analytical balance?
Ans: Hygroscopic, volatile and liquid substances are weighed in
weighing bottle. Care should be taken about not spilling these
chemicals.
Q 73 Describe two methods of weighing.
Ans: (a) Weighing by difference: Take a clean and dry weighing bottle,
add the sample in it and weigh accurately. Transfer the weighed
sample to the conical flask, after removing the stopper. Replace
the stopper and weigh the bottle. The difference between the
two weights is the weight of the sample.
Weight of weighing bottle + sample = ‘x’ g
Weight of weighing bottle after transfer of sample = ‘y’ g
Weight of sample = (x – y) g
(b) Weighing by addition: Clean and dry weighing bottle/watch
glass is weighed. Add the sample in small portions until
correct weight is added. Weigh the bottle and contents.
Transfer the contents. Wash the container with water and
washings are added in receiving vessel.
PURIFICATION PROCESSES
Q 74. How will you purify an impure sample?
Ans: An impure sample can be purified by crystallization or by sub-
limation.
Q 75 What is crystallization?
Ans: Crystallization is the process of purifying solid chemicals by
dissolving them in suitable solvent, forming a supersaturated
solution and then allowing the solid to crystallize when the
solution cools slowly.
Q 76. How crystallization is done?
Ans: Crystallization involves following steps:
1. Dissolve the solid in suitable solvent at or near the boiling
point.
2. Filter the hot solution to remove insoluble particles and dust,
i.e. undissolved impurities.
3. Allow the hot solution to cool gradually.
4. The dissolved substance starts appearing slowly in the form
of crystals.
General Questions 13
5. Separate the crystals from mother liquor. Dry and test for
purity.
6. Repeat the procedure if required.
Q 77 How recrystallization is carried out for inorganic soilds
which are too soluble?
Ans: The soild can be precipitated/crystallized from a concentrated
aqueous solution by addition of a liquid (miscible with water)
in which it is less soluble. Ethanol is used for this purpose as
many inorganic compounds are almost insoluble in ethanol.
Q 78 How recrystallisation is carried out when solubility does
not vary sufficiently with temperature?
Ans: Same as for previous answer.
Q 79 What is sublimation?
Ans: Sublimation is the process in which solid gets directly
converted to vapour state on heating and on cooling, the
vapours get converted into solid state without the inter-
mediate liquid state.
Q 80 When sublimation is used as method of purification?
Ans: Sublimation is used to separate volatile substances from non-
volatile impurities, e.g. iodine, arsenic trioxide, ammonium
chloride can be purified in this way.
Q 81 How sublimation is carried out ?
Ans: The material to be purified is gently heated in a porcelain
dish and the vapour produced is condensed on the walls of
the funnel, which is placed in inverted position on the
evaporating dish. The stem of the funnel is plugged with
cotton wool.
Q 82 What is filtration?
Ans: Filtration is the process of separating the solid from liquid by
using suitable filtering media. Filtration can be used to remove
undissolved impurities. Filtration is used can be separating
the precipitate from the mother liquor.
Q 83 Name filtering media/systems.
Ans: Filter paper, sintered glass filter, Buchner funnel made of
porcelain/silica are some filtering media. The pore size of
filtering media should be selected depending upon purpose
of filtration.
14
Viva Voce in
Pharmaceutical Chemistry
PERIODIC TABLE
Q 84 What do you understand by periodic table?
Ans: Periodic table is a tabular arrangement of elements according
to increasing order of atomic numbers so that elements with
similar chemical properties are in the same column.
Q 85 How many periods are there in periodic table?
Ans: Periodic table has 7 periods.
Q 86 How many groups are there in periodic table?
Ans: Periodic table has 8 major groups. Group I to VII are
subclassified into a and b and there is a group ‘o’ which
indicates the gases. Total there are 16 groups.
Q 87 What is atomic mass/atomic weight?
Ans: Atomic mass is sum total of the weight of protons, neutrons
and electrons present in that element.
Q 88 What is atomic number?
Ans: Atomic number is the weight of the protons present in the
element.
Q 89 Which are the signature elements of group IA?
Ans: Sodium and potassium are signature elements of group IA.
Q 90 Which are the signature elements of group IIA?
Ans: Signature elements of group IIA are magnesium and calcium.
Q 91 Which is the signature element of group VIII?
Ans: Iron is the signature element of group VIII.
Q 92 Name signature elements of group IB.
Ans: Copper and silver.
Q 93 Name signature elements of group IIB.
Ans: Zinc and mercury.
Q 94 Name signature elements of group VIIA.
Ans: Fluorine, chlorine, bromine, iodine are signature elements of
group VIIA.
Q 95 Carbon, nitrogen and oxygen belong to which period?
Ans: Carbon, nitrogen and oxygen belong to second period.
General Questions 15
Q 96 Hydrogen belongs to which group and which period?
Ans: Hydrogen belongs to Ist period and IA group.
Q 97 Name inert gases.
Ans: Helium, neon, argon, krypton, xenon and radon are inert gases
and they are present in group VIII.
Q 98 What does a period signify?
Ans: Rows of elements are called periods. The period number of
an element signifies the highest unexcited energy level for an
electron in that element. Elements of the same period have
the same number of electron shells.
Q 99 What does a group signify?
Ans: A group signifies that all elements belonging to group
have same valence electron structures. The elements of
the same group have a common valency which is equal
to the number of group. Elements in the same subgroup
have similar physical and chemical properties.
Q 100 What does the subgroup ‘A’ signify?
Ans: Subgroup ‘A’ represents alkali metals while subgroup B
represents transition element members.
LABORATORY HAZARDS AND FIRST AID
Q 101 What safety precautions should be observed in the
laboratory?
Ans:
1. Students should always wear laboratory coat.
2. Hazardous chemicals should be handled after wearing hand
gloves and protective goggles.
3. Concentrated acids should be capped, replaced to their rack
immediately after use.
4. Inflammable chemicals such as ethanol, ether should not be
used near burner.
5. Never taste a chemical.
6. Do not smell a chemical by rapid inhalation.
7. Avoid skin contact of chemicals.
8. Use fume cupboards/hoods when toxic fumes are released.
16
Viva Voce in
Pharmaceutical Chemistry
9. Do not attempt unauthorized experiments.
10. Maintain discipline in the laboratory, do not play around in
the laboratory.
Q 102 Why fire hazards occur in chemistry laboratories?
Ans: Fire hazards occur in chemistry laboratories because volatile
and flammable chemicals especially solvents are used in
experiments.
Q 103 How should we pipette out harmful or evaporable sub-
stances?
Ans: Strong acids and other evaporable substances should not be
pipetted out by mouth. Instead use a pipette bulb.
Q 104 How would you dilute concentrated acids?
Ans: Acids must be diluted by slowly adding them to water while
mixing. Water should never be added to concentrated acid to
avoid splattering.
Q 105 What would you do when concentrated acid splashes on the
skin?
Ans: Wash the area thoroughly with water. Bathe the affected skin
with cotton wool soaked in 5% aqueous sodium carbonate
solution.
Q 106 How would you treat the skin splashed with alkali?
Ans: Wash the area thoroughly with water. Bathe the affected area
with cotton wool soaked in 5% acetic acid or vinegar.
Q 107 What would you do if acid splashes in the eye?
Ans: Spray water from a wash bottle into the corner of the eye. Put
4 drops of 2% aqueous sodium bicarbonate into the eye.
Q 108 What is the first aid measure for splashing of alkali in the
eye?
Ans: Spray the corner of eye with water using wash bottle. Put
4 drops of saturated solution of boric acid.
Q 109 What first aid should be employed when a person swallows
acid?
Ans: Make the patient drink some 5% soap solution immediately.
Make him gargle with the soap solution. Give him 3–4
glasses of ordinary water for drinking. If the lips and tongue
are burned by the acid, rinse thoroughly with water and
bathe with 2% aqueous sodium bicarbonate.
General Questions 17
Q 110 What is the treatment if the student swallows alkali
solution?
Ans: Make him drink 5% solution of acetic acid or lemon juice or
dilute vinegar. Make him gargle with same solution. Make
him drink 3–4 glasses of ordinary water.
If the lips and tongue are burned by the alkali, rinse
thoroughly with water and bathe with 5% acetic acid.
18
Viva Voce in
Pharmaceutical Chemistry
GENERAL QUESTIONS
Q 111 What do you understand by impurity?
Ans: Impurity is the foreign matter like glass particles, plastic
fragments, porcelain particles or chemical substances like
lead and arsenic salts, chloride and sulphate compounds, iron
salts, etc.
Q 112 Is it possible to obtain absolute pure substance?
Ans: A state of absolute purity is almost unattainable. Even analy-
tically pure compounds are having minute traces of impurities.
Q 113 Why it is not desirable to use 100% pure drug?
Ans: Purification of chemicals is an expensive process. Therefore
the drug should not be purified more than needed, otherwise
the cost of medicines would be beyond the reach.
Q 114 Which factors contribute to the purity of a substance?
Ans: Purity of the substance depends upon method of manufacture,
type of crystallization and purification process and stability
of the substance.
Q 115 What are the different sources of impurities in pharmaceutical
substances?
Ans: The different sources of impurities in pharmaceutical sub-
stances are:
1. Raw material.
2. The manufacturing process.
• Intermediates formed.
• Reagents, solvents and catalysts used.
• Metal of the reaction vessel.
3. Chemical decomposition of drug in presence of air, moisture.
Limit Tests
1
18
Limit Tests 19
4. Improper storage and deliberate adulteration.
5. Accidental substitution.
6. Deleberate adulteration with spurious or useless materials.
Q 116 Name the common impurities for which the pharmacopoeia
prescribes limit tests.
Ans: The common impurities for which the pharmacopoeia
prescribes limit tests are arsenic, heavy metals, chlorides,
sulphates, iron.
Q 117 What is the meaning of limit tests?
Ans: Limit tests are semiquantitative or quantitative tests designed
to identify and control small quantities of impurity which are
likely to be present in the substance.
Q 118 What does the limit in limit test indicates?
Ans: Limit indicates the level of tolerance of impurity in a given
substance. Beyond this level, the impurity would produce the
harmful effects.
Q 119 What is the importance of limit tests? Why should limit tests
be performed?
Ans: Limit tests should be performed to ensure the quality of the
substance. The drugs should be free from physiologically
harmful impurities or the impurity level should be acceptable.
Q 120 Which factors are taken into consideration before setting
the limits?
Ans: Before setting limit for any impurity following factors are taken
into consideration.
1. Intended use of the official compound
2. Safety considerations
3. Cost of production
It is necessary to strike a balance so that the drug is sufficiently
pure to ensure reasonable levels of safety and efficacy, yet
cost effective.
Q 121 Why does a drug need to pass the limits set in pharmacopoeia?
Ans: Adherence of the drug to official standards ensures consistent
therapeutic response, acceptable level of potency and freedom
from toxicity.
Q 122 Which apparatus is used for performing limit tests?
Ans: A pair of Nessler cylinders made of clear, lead-free glass is
used for performing limit tests.