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110
Viva Voce in
Pharmaceutical Chemistry
Q 559 How do you calculate percentage purity of calcium gluconate?
Ans:
1. From the factor, we know that
1 ml of 0.05 M disodium edetate 0.02242 g of C
12
H
22
CaO
4
.
H
2
O
2. Say the molarity of prepared disodium edetate solution is ‘m’
3. The volume of disodium edetate consumed by calcium ions
= V ml
4. Then
If 1 ml 0.05 M disodium edetate 0.02242 g
V ml of ‘m’ M disodium edetate
V m 0.02242
0.05
5. ‘W’ g is the weight of calcium gluconate. Then V ml correspond
to W g of C
12
H
22
CaO
4
, H
2
O
W =
V × m × 0.02242
0.05
6. If W
V × m × 0.02242
0.05
then,
100 g of calcium gluconate
V × m × 0.02242
0.05 W
× 100 g of C
12
H
22
CaO
4
, H
2
O
% purity =
V × m × 0.02242
0.05 × W
× 100
ASSAY OF SODIUM CHLORIDE (BACK TITRATION)
Q 560 What is the principle behind assay of sodium chloride?
Ans: Sodium chloride is assayed using precipitation (argentimetric)
titration. It is done by Volhard’s method. The chloride ions
react with silver nitrate solution and form silver chloride
precipitate. The excess silver nitrate is back titrated with
ammonium thiocyanate solution.
Q 561 Give the reactions involved in sodium chloride assay.
Ans:
Assays 111
At equivalence point
Q 562 What are the standards for sodium chloride as per I.P. 2010?
Ans: As per IP 2010, sodium chloride should contain not less than
99.0% and not more than 100.5% of NaCl.
Q 563 Why dibutyl phthalate is added in the analyte solution?
Ans: Dibutyl phthalate is added to cover the silver chloride
particles, otherwise silver chloride would interfere with the
end point.
Q 564 What is the procedure of assay of sodium chloride as per
IP 2010?
Ans:
1. Weigh 0.1 g of sodium chloride.
2. Dissolve in 50 ml of water.
3. Add 50 ml of previously standardised solution of 0.1 M silver
nitrate, 5 ml of 2 M nitric acid and 2 ml of dibutyl phthalate.
4. Add 2 ml of ferric ammonium sulphate indicator.
5. Shake vigorously to coagulate the precipitated silver chloride.
6. Titrate with 0.1 M ammonium thiocyanate until the colour
becomes reddish yellow.
7. Take burette reading.
Q 565 Which indicator is used in the assay of sodium chloride?
Ans: Ferric ammonium sulphate is used as indicator, which
becomes reddish brown at equivalence point.
Q 566 How the factor is calculated in sodium chloride assay?
Ans: From the reaction, we know that
1 mole of AgNO
3
1 mole of NaCl
1000 ml of 1 M AgNO
3
58.44 g of NaCl
112
Viva Voce in
Pharmaceutical Chemistry
1 ml of 0.1 M AgNO
3
58.44
10 × 1000
g of NaCl
1 ml of 0.1 M AgNO
3
= 0.005844 g of NaCl
Q 56 7 How the percentage purity is calculated in sodium chloride assay?
Ans:
1. Molarity of ammonium thiocyanate solution = M
1
2. Volume of ammonium thiocyanate used = V
1
3. Molarity of silver nitrate solution = M
2
4. Volume of silver nitrate added = V
2
5. Weight of the sodium chloride = W
6. Volume of silver nitrate utilised for precipitation of W g of
sodium chloride = (M
2
×V
2
) – (M
1
× V
1
) = Z
If 1 ml 0.1 M AgNO
3
0.005844 g of NaCl
then Z ml of ‘M
2
’ M AgNO
3
2
0.005844 × Z × M
0.1
Z ml of silver nitrate corressponds to W g of sodium chloride
W g of sodium chloride
2
0.005844 × Z × M
0.1
g of NaCl
then 100 g of sodium chloride =
2
0.005844 × Z × M
0.1 × W
×100
Q 568 What are the uses of sodium chloride?
Ans:
1. Electrolyte replenisher in ORS.
2. Food preservative.
3. In preparation of tooth paste, soaps, detergents.
4. For de-icing road, as it lowers the freezing point of ice.
5. Useful in manufacturing pulp and paper.
6. For setting dyes in textiles and fabric.
7. Source of industrial chlorine and sodium hydroxide.
ASSAY OF ASCORBIC ACID
Q 569 Describe the procedure of the assay of ascorbic acid.
Ans: The ascorbic acid is dissolved in distilled water and acidified
with sulfuric acid to stabilize the ascorbic acid. This solution
is titrated with standard solution of iodine using starch
Assays 113
solution as indicator until a persistent blue violet colour is
obtained.
Q 570 What is the reaction occurring in the assay of ascorbic acid?
Ans: This is a redox titration in which ascorbic acid is oxidised to
dehydroascorbic acid by iodine and in process iodine is
reduced to iodide.
Q 571 What is the end point in the assay of ascorbic acid?
Ans: The change is from colourless to permanent blue at the end
point in the assay of ascorbic acid.
Q 572 What are the standards of ascorbic acid given in IP?
Ans: As per IP, ascorbic acid should contain not less than 99% and
not more than 100.5% of C
6
H
8
O
6
.
Q 573 What is the titrant used in the assay of ascorbic acid?
Ans: The titrant used in the assay of ascorbic acid is ascorbic acid
solution.
Q 574 What is the standard solution used in the assay of ascorbic
acid?
Ans: The standard solution used in the assay of ascorbic acid is
0.05 M iodine.
Q 575 What is the indicator used in the assay of ascorbic acid?
Ans: The indicator used in the assay of ascorbic acid is starch
solution.
Q 576 What is the use of ascorbic acid?
Ans: Ascorbic acid is used as antiscorbutic and antioxidant.
Q 577 What is the factor used in calculating the amount of ascorbic
acid in the assay of ascorbic acid and how is it calculated ?
Ans: The factor used in calculating the amount of ascorbic acid in
the assay of ascorbic acid is
Each ml of 0.05 M iodine corresponds to 0.008806 g of C
6
H
8
O
6
.
114
Viva Voce in
Pharmaceutical Chemistry
Factor Calculation:
1 mole of iodine = 1 mole of C
6
H
8
O
6
1000 ml of 1 M iodine = 176.124 g of C
6
H
8
O
6
1 ml of 0.05 M iodine = 0.008806 g C
6
H
8
O
6
ASSAY OF IBUPROFEN
Q 578 Describe the assay of ibuprofen.
Ans: In ibuprofen assay, ibuprofen is dissolved in ethanol and the
solution is titrated with sodium hydroxide using pheno-
lphthalein solution as indicator until the pink colour
disappears.
Q 579 Explain the monoprotic acid behaviour of ibuprofen with
the help of an example.
Ans: Monoprotic acids are those acids which donate only one
proton to the base. In the acid–base titration of ibuprofen, it
donates one proton to one mole of sodium hydroxide making
it monoprotic acid.
Q 580 What is the end point in the assay of ibuprofen?
Ans: The change from colourless to permanent pink is the end point
in the assay of ibuprofen.
Q 581 What are the standards of ibuprofen given in IP?
Ans: As per IP, ibuprofen should contain not less than 98.5% and
not more than 101% of C
13
H
18
O
2,
calculated on the dried basis.
Q 582 What is the titrant used in the assay of ibuprofen?
Ans: The titrant used in the assay of ibuprofen is ibuprofen solution.
Q 583 What is the standard solution used in the assay of ibuprofen?
Ans: The standard solution used in the assay of ibuprofen is 0.1 M
sodium hydroxide.
Q 584 What is the indicator used in the assay of ibuprofen?
Ans: The indicator used in the assay of ibuprofen is phenolph-
thalein solution.
Assays 115
Q 585 What is the use of ibuprofen?
Ans: Ibuprofen is used as an anti-inflammatory and analgesic.
Q 586 What is the factor used in calculating the amount of
ibuprofen in the assay of ibuprofen and how is it calculated?
Ans: The factor used in calculating the amount of ibuprofen in the
assay of ibuprofen is
Each ml of 0.05 M iodine corresponds to 0.02063 g of C
13
H
18
O
2.
Factor Calculation:
1 mole of NaOH = 1 mole of C
13
H
18
O
2
1000 ml of 1 M NaOH = 206.3 g of C
13
H
18
O
2
1 ml of 0.1 M NaOH = 0.02063 g of C
13
H
18
O
2
Q 587 Explain the principle behind the assay of ibuprofen.
Ans: It is a neutralization titration. The carboxylic acid group of
ibuprofen is titrated with NaOH solution using phenolph-
thalein as indicator. The number of moles or amount of sodium
hydroxide consumed in reaction indicates the amount of
ibuprofen present in the sample as there is molecular
equivalence between the acid (ibuprofen) and the base
(NaOH).
116
Viva Voce in
Pharmaceutical Chemistry
GENERAL QUESTIONS
Q 588 What is normality?
Ans: It is the number of gram equivalents of the substance dissolved
per litre of the solution.
Q 589 How would you prepare x N solution of a substance?
Ans: x N solution is prepared by dissolving x gram equivalent
weight of the active substance in solvent/water and then the
volume is made up to 1000 ml by adding the solvent/water.
Q 590 What is molarity?
Ans: It is the number of gram moles of the substance dissolved per
litre of solution.
Q 591 How would you prepare x M solution?
Ans: x M solution is prepared by dissolving x gram molecule of
the reagent in solvent/water and then the volume is made
up to 1000 ml by further addition of solvent/water.
Q 592 What is fuming chamber/fume cupboard? State its use.
Ans: Fuming chamber is an enclosed chamber fitted with exhaust
fan and an outlet in the open air. Fuming chamber is used to
remove the hazardous fumes produced in chemical reactions
which otherwise would harm the people working in the
laboratory.
Q 593 Give the concentration of concentrated sulphuric acid used
in the laboratory.
Ans: Concentrated sulphuric acid should contain not less than
97.00% w/w of H
2
SO
4
. The approximate normality/molarity
of concentrated sulphuric acid is 36 N or 18M.
Fundamentals of
Preparative Organic
Chemistry
5
116
Fundamentals of Preparative Organic Chemistry 117
Q 594 Give the concentration of concentrated hydrochloric acid
used in the laboratory.
Ans: Concentrated hydrochloric acid should contain 35–38% w/w
of HCl. The approximate normality of concentrated hydro-
chloric acid is 11.5 N.
Q 595 Give the concentration of concentrated nitric acid used in
the laboratory.
Ans: Concentrated nitric acid should contain 69.0–71.0% w/w of
HNO
3
. The approximate normality of concentrated nitric acid
is 16 N.
Q 596 Give the concentration of glacial acetic acid used in the
laboratory.
Ans: Glacial acetic acid should contain not less than 99.0% w/w
C
2
H
4
O
2
. The approximate normality of glacial acetic acid is
17.5 N.
Q 597 What is the difference between glacial acetic acid and acetic
acid?
Ans: Glacial acetic acid contains not less than 99.0% w/w of
CH
3
COOH. The approximate normality is about 17.5 N.
Acetic acid contains approximately 33% w/w of CH
3
COOH.
Dilute 315 ml of glacial acetic acid to 1000 ml with water to
get acetic acid.
Q 598 Give the concentration of dilute hydrochloric acid. How is
it prepared?
Ans: Dilute hydrochloric acid contains about 10% w/w of HCl. Mix
274 g of hydrochloric acid with 726 g of purified water.
Q 599 Give the concentration of dilute nitric acid. How is it prepared?
Ans: Dilute nitric acid contains approximately 10% w/w of HNO
3
.
Dilute 106 ml of nitric acid to 1000 ml with water to get dilute
nitric acid.
Q 600 Give the concentration of dilute sulphuric acid. How is it
prepared?
Ans: Dilute sulphuric acid contains approximately 10% w/w of
sulphuric acid. Dilute 57 ml of sulphuric acid to 1000 ml with
water to produce dilute sulphuric acid. The calculated amount
of water is taken and slowly, with stirring and cooling, the
calculated amount of concentrated acid is added to it.
118
Viva Voce in
Pharmaceutical Chemistry
Q 601 Give concentration of dilute acetic acid.
Ans: Dilute acetic acid contains approximately 6% w/w of
CH
3
COOH. Dilute 57 ml of glacial acetic acid to 1000 ml.
Q 602 Give the concentration of strong ammonia solution.
Ans: Strong ammonia solution contains 25% w/w of ammonia. The
strength is about 13.5 M.
Q 603 Give the concentration of dilute ammonia solution.
Ans: Dilute ammonia solution contains approximately 10% w/w
of NH
3
, i.e. ammonia. Dilute 425 ml of strong ammonia
solution to 1000 ml to get dilute ammonia solution.
Q 604 What is soda-lime chemically? What is its use?
Ans: It is a mixture of sodium hydroxide, or sodium hydroxide
and potassium hydroxide, with calcium hydroxide. It is used
to absorb carbon dioxide. It absorbs about 20% of its weight
of carbon dioxide.
Q 605 What is analytical reagent grade chemical?
Ans: Analytical reagent implies that the chemical is of a high degree
of purity wherein the limits of various impurities are known
and are below the limits stated in Indian Pharmacopoeia.
Q 606 What is laboratory reagent grade chemical?
Ans: Laboratory reagent grade implies that it is chemically pure
grade material, which is not necessarily required to be tested
for limiting or absence of certain impurities. The purity is less
than AR grade chemicals.
Q 607 What is fuming nitric acid?
Ans: Fuming nitric acid contains about 95% w/w of HNO
3
. It is a
fuming liquid.
Q 608 How x M sulphuric acid is prepared?
Ans: Solution of x M molarity is prepared by carefully adding
54 x ml of sulphuric acid to an equal volume of water and
diluting to 1000 ml with water.
Q 609 How x N sulphuric acid is prepared?
Ans: x N sulphuric acid is prepared by diluting 27 x ml of sulphuric
acid to 1000 ml with water.
Q 610 How x M hydrochloric acid is prepared?
Ans: Solutions of x M hydrochloric acid is prepared by diluting 85
x ml hydrochloric acid to 1000 ml with water.
Fundamentals of Preparative Organic Chemistry 119
Q 611 How x N hydrochloric acid is prepared?
Ans: x N hydrochloric acid is same as x M HCl and is prepared
by diluting 85 x ml of hydrochloric acid to 1000 ml with
water.
Q 612 How x M HNO
3
is prepared?
Ans: x M HNO
3
is prepared by diluting 63 x ml of nitric acid to
1000 ml with water.
Q 613 How x N HNO
3
is prepared?
Ans: x N HNO
3
is same as x M HNO
3
and is prepared by diluting
63 x ml of nitric acid to 1000 ml with water.
SOLUBILITY
Q 614 What is the importance of performing solubility tests in
detection of organic compounds?
Ans: Solubility detection reveals whether the compound is polar
or non-polar, strongly acidic or weakly acidic, strongly basic
or weakly basic, neutral or not. It also helps in deducing
molecular weight.
Q 615 How is solubility test performed?
Ans: Generally, 0.1 g of solid or 0.2 ml of liquid is taken and 3 ml of
solvent is added. Formation of homogenous liquid indicates
that the substance is soluble.
Q 616 When a sample is soluble in water, what is the inference?
Ans: Since water is a polar solvent, it dissolves polar compounds.
Non-polar hydrocarbons are not soluble. Polar compounds
such as alcohols, aldehydes, ketones, acids, amides, nitriles
and amines with less than four carbon atoms are soluble.
Q 617 If the substance is soluble in dilute sodium hydroxide
solution as well as dilute sodium bicarbonate solution, what
inference would you draw?
Ans: When the substance is soluble in basic solutions, it is acidic
in nature. The compound may be either strong acid or weak
acid. Strongly acidic substance would dissolve in dilute
sodium hydroxide solution and would produce effer-
vescence with sodium bicarbonate solution (e.g. carboxylic
acids), while weakly acidic substance would not produce
effervescence with sodium bicarbonate and would not
dissolve in it. So, it would be strongly acidic substance.