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 H2SO4using 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
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