TESTING AND PURITY ANALYSIS FOR
CHEMICALS
Prof. Aravin
Prince Periyasamy, M.Tech
DKTE Textile
& Engineering Institute, Ichalkaranji, Kolhapur, India.
E-Mail: aravinprince@gmail.com Blog: www.aravinprince.blogspot.in
1.
DETERMINATION
OF AVAILABLE CHLORINE IN SODIUM HYPOCHLORITE SOLUTION
Method
A:
Pipette 25 ml of
the sample and transfer to a 500 ml volumetric flask containing about 300 ml
ice cold water. Dilute to the mark with ice cold water and mix well.
Take 25 ml
aliquot in a 250 ml conical flask. Add about 50 ml ice cold water and about 2
gm NaHCO3. Titrate with N/10 arseneous acid solution. First test
with KI-starch indicator papers when the blue test becomes faint. Add about 1
gm solid KI and starch solution. Titrate further till the blue colour
disappears.
ml N / 10
arseneous acid ´
0.003546 ´
500 ´
100
________________________________________
= % available Chlorine (w / v)
25 ´ 25
Method
B:
Take 10 ml
sample in 100 ml standard volumetric flask and make up to the mark with
distilled water. Call this solution ‘A’. Take 10 ml solution from ‘A’ in 100 ml
conical flask containing about 25 ml distilled water. Add 2-3 gms. KI crystals
and 5 ml glacial acetic acid. Quickly stopper the flask, shake well and titrate
against N / 10 Na2S2O3 solution using starch
solution as indicator till discharge of Blue colour.
Rd ´ N ´ 3.55 ´ 100
________________________________________
= Available Chlorine (gms./ L)
0.1 ´ 10 ´ 10
Rd = ml. of N /
10 Na2S2O3
N = Normality of
N/ 10 Na2S2O3
2. DETERMINATION
OF Na2O: SiO2 IN SODIUM SILICATE
About 5 gms. of
the paste sample is weighed out accurately and transfer to 100 ml volumetric
flask with water and make upto the mark with water. Stir well. From this
solution, pipette out 10 ml in 250 ml conical flask containing 50 ml water and
titrate against 1 N H2SO4 using methyl orange indicator.
Call this burette reading “M”. Further add sodium fluoride (about 5 gm) and the
second titration is made to methyl red end point when liberated sodium
hydroxide reacts with the acid. Call this burette reading “P”.
Calculation:
“M” ´ Normality ´
31
________________________________________
= % Na2O
1 ´ Weight of sample
“P-M” ´ Normality ´ 60
________________________________________
= % SiO2
1 ´ 4 ´ Weight of sample
3. DETERMINATION
OF HARDNESS IN WATER
Hardness in water is caused
mainly by the presence in solution of various compounds of calcium and
magnesium. It is customary and necessary to distinguish between two kinds of
hardness:
(a)
Temporary
Hardness (sometimes referred to as Carbonate Hardness)
Temporary
Hardness results from the presence of bicarbonates of calcium and magnesium,
and is so called from the fact that it is for the most part destroyed by
boiling.
(b)
Permanent
Hardness (Non-carbonate Hardness)
Permanent
Hardness is caused by the presence of the sulphates, chlorides and nitrates of
calcium and magnesium, and is not destroyed by boiling at atmospheric pressure.
In order to
express the hardness of water quantitatively it is usual to calculate the
calcium and magnesium compounds present in terms of their equivalent of calcium
carbonate (CaCO3). The hardness is then stated in terms of ‘parts
CaCO3 per 100,000’.
E.D.T.A. Method:
Special reagents required:
- Reagent A – N / 50 E.D.T.A. i.e. Disodium dihydrogen ethylene diammine tetraacetate. Dissolve 3.72 gms of crystalline dihydrate in distilled water and dilute to 1 litre.
- Reagent B – Ammonia buffer solution
Add
16.875 gms of Ammonium chloride to 142.5 cc of Ammonium hydroxide solution (sp.
gr. 0.880) and dilute to 225 cc with distilled water.
Separately
dissolve 0.1540 gms of Magnesium sulphate (MgSO4, 7 H2O)
in 12.5 cc distilled water and add 0.2325 gms of solid E.D.T.A. Add this to
Ammonium hydroxide / Ammonium chloride mixture and dilute with distilled water
to 250 cc.
- Reagent C – Total hardness indicator
Add 0.5 gm Solochrome Black
GDFA to 100 cc of alcohol (industrial methylated spirit). Warm to dissolve the
dyestuff and add 4.5 gms of Hydroxylamine hydrochloride. Allow to stand
overnight and filter.
Note:
This solution should not be used after one month.
Procedure:
Total
Hardness
Transfer 100 cc
sample of water to porcelain casserole. Add 2 cc Ammonium Buffer solution
(Reagent B) and six drops of indicator (Reagent C). Titrate immediately with
E.D.T.A. solution until the solution has lost all traces of red colour. At this
point, final colour is usually pure blue but with some water a neutral grey end
point is obtained.
Note: When
hardness is greater than 250 ppm as CaCO3, use 50 cc or smaller
sample.
Tire reading ´ 1000
____________________ = Total Hardness
(ppm as CaCO3)
Sample taken in ml.
[Note:
1o German hardness = 18 ppm]
4. DETERMINATION
OF PURITY OF SODIUM CARBONATE (SODA ASH)
Accurately weigh
5.50 gms. of the sample. Transfer to a 500 ml conical flask with 100 ml distilled
water and dissolve completely by shaking. Observe for the presence of
turbidity. Add 5 to 6 drops of indicator methyl orange solution and titrate
with a standard N / 1 Sulphuric acid solution till the yellow colour changes to
orange red.
Calculation:
ml of N / 1
Sulphuric acid ´
0.053 ´
100
________________________________________
= % Na2CO3 alkalinity
5.3
5. ANALYSIS
OF CAUSTIC SODA FLAKES:
Strength as NaOH and Carbonate as Na2CO3
Weigh out
accurately from a stoppered weighing bottle 18-20 gms. of the material into a
500 ml beaker. Add 250 ml cold carbon dioxide free water. Stir until dissolved,
cool, transfer into a 500 ml measuring flask, dilute to the mark at room
temperature with carbon dioxide free water and mix well. Call this solution
‘A’.
Transfer 50 ml
solution ‘A’ to a 250 ml conical flask, dilute to 150 ml with water and titrate
with N / 1 Hydrochloric acid using phenolphthalein as indicator, till the pink
colour disappears. Take this reading as P ml. Then add 0.5 ml bromophenol blue
solution and further titrate with N/1 Hydrochloric acid until the blue colour
changes to greenish blue. Take this reading as M ml.
Calculation:
M – 2(M – P) ´ 40
________________________________________
= % Strength as NaOH
Weight taken
2(M – P) ´ 53
________________________________________
= % Carbonate as Na2CO3
Weight taken
6. ANALYSIS
OF SODIUM HYDROSULPHITE (SODIUM DITHIONITE) (HYDROS)
Remove the top
layer of the sample and weigh accurately in a tared weighing bottle 8.0 – 8.5
gms. of the material remaining in the sample bottle without mixing. Place 40 ml
40% formaldehyde solution and 910 ml boiled-out and cooled water in a 1 litre
volumetric flask with a short neck (about 1 inch above the graduation mark),
mix well, give the liquid in the flask a swirling motion, and pour in the
weighed sample through a short stemmed funnel. Wash the funnel and weighing
bottle rapidly with boiled-out and cooled water, dilute to the mark, and mix
well. The swirling motion given to the liquid prevents the dithionite from
forming a cake at the bottom of the flask. Allow the solution to stand for at
least 15 minutes so that the reaction between the dithionite and formaldehyde
may be complete. Call this solution A.
Place about 100
ml boiled-out and cooled water in a 500 ml conical flask, and add 25 ml
Solution A by means of a pipette. Add 5 ml glacial acetic acid and 50 ml N/10
iodine, allow to stand for 2 minutes, and titrate the excess of iodine with
N/10 sodium thiosulphate, slowly towards the end-point, using freshly prepared
starch solution as indicator added towards the end of the titration.
Carry out a
control test using 25 ml boiled-out and cooled water instead of 25 ml Solution
A.
Calculation:
Let, A = ml N/10
Na2S2O3 required in control test
and B = ml N/10 Na2S2O3
required in test
(A-B) ´
17.41
____________________ =
Strength calculated as % Sodium Hydrosulphite
Weight
taken
(M.W. 174.1)
7. ANALYSIS
OF GLAUBER’S SALT (SODIUM SULPHATE)
Take 1 gm of the
sample and dilute it with 100 ml distilled water in volumetric flask. Take 50
ml Acetone in conical flask and add 10 ml of the above solution along with 2 ml
Di-thiozone indicator and add 1 to 2 drops of Nitric acid till colour changes.
Add 2 ml Buffer solution and titrate with 0.01 M Pb(NO3)2
till colour changes from blue-green to brick red.
Calculation:
Burette reading´
0.142 ´
100
___________________________ = % Na2SO4
Weight taken ´
10
Note:
Di-Thiazone indicator –
0.05 gms
indicator + 100 ml Acetone
Buffer solution –
Take 200 ml.
water. Add 46 ml of Dichloro acetic acid, followed by 40 ml 10 N NH3
& adjust pH 7.0. Add 22 ml of Dichloro acetic acid and adjust pH 1.5 – 2.0.
Make total volume of 500 ml.
0.01 M Pb(NO3)2 –
Dissolve 16.560
gms. of Pb(NO3)2 in 500 ml distilled water. Take 50 ml of
this solution and dilute to make 500 ml with distilled water.
8. DETERMINATION OF PURITY OF SODIUM CHLORIDE
(COMMON SALT)
Dissolve 5.845
gms of the sample in water and make upto 1000 ml volume in a volumetric flask.
Mix well.
Pipette 50 ml
aliquot of the above solution into a 500 ml Erlenneyer flask, add 4 drops of
10% w/v K2CrO4 indicator solution and about 0.5 gm of
c.p. CaCO3. Titrate against a standard N/10 silver nitrate solution
until the orange pink tint due to Ag2CrO4 precipitate is
produced. This indicates the end point.
Calculation:
ml of N / 10 AgNO3 required ´ 0.005845 ´ 1000
´
100
_______________________________________ = ml of N / 10 AgNO3
required ´
2 = % NaCl.
50 ´
5.845
9.
DETERMINATION
OF PURITY HYDROGEN PEROXIDE
Weigh 2 gms of
sample in glass stopper bottle & dilute it up to 250 ml with volumetric
flask. Pipette out 10 ml of this solution, add 50 ml of water & 20 ml of
10% sulphuric acid & titrate against 0.1 KMNO4 to the appearance
of faint pink colour.
.
Calculation:
Burette reading´
42.52 ´
Normality of KMNO4
___________________________ = % Purity
Weight taken
10 Volume = 3%
of H2O2
very useful
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