Determination of chloride in water by argentometric titration method

 Determination of chloride in water by argentometric titration method

AIM:

To determine the amount of chloride present in a given sample by argentometric titration method.

PRINCIPLE:

Generally all natural water contains chloride ions.even in distilled water.sea water contains  large amount of chloride.potassium chromate is an indicator that indicate the end point of chloride at the PH of Neutral to slightly alkaline. this is argentometric titration for determination of chloride in which the chloride ions react with silver of silver nitrate to form silver chloride.when chloride ions are completely converted into silver chloride,the remaining silver ions starts react with chromate ions of indicator and form silver chromate which is brick red or brown in Color.that is the end point.

STEP 1:   Cl- + AgNo3 -----> Agcl (white precipitate).now the chloride ions are completely converted to silver chloride.

STEP 2:               AgNO3 + K2CrO4 -------> Ag2CrO(brick red)

APPARATUS REQUIRED:

1)Brown bottle

2)Conicle flasks.

3)Brown burette.

4)Standard volumetric flasks.

5)Glass rod.

6)Beakers.

7)PH meter.

8)Filter papers

9)Glass funnel

CHEMICALS REQUIRED:

1)Potassium chromate.

2)Silver nitrate.

3)Reagent grade water (Distilled water or millipore water).

4)Sodium chloride.

5)NaOH or hydrochloric acid.

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REAGENTS AND PREPARATIONS:

1)0.0141N AgNO3:

Dissolve 2.3951g  of    AgNO3 in reagent grade water and make  up to 1000ml  in volumetric   flask.store.  this solution in brown bottle.

2)Potassium chromate indicator:

Dissolve 5g of potassium chromate salt in little distilled  water.add 0.0141N silver nitrate solution until a red precipitate form.leave it for 12 hours.then filter the precipitate and make up to 100ml with reagent grade water.

3)Sodium chloride solution for standarization:

Dry the sodium chloride in oven at 140 degree Celsius  for an hour.then weight 0.0824g and dissolve in reagent grade water.then make up to 100ml.

PROCEDURE:

 

Wash the Conicle Flask thoroughly with millipore water.pour the sample aliquot.adjust the sample PH to 7.5 to 8 using 0.02N acid or base.add 4 drops of potassium chromate indicator.the colour become yellow if chloride ions present otherwise brick red.start titrate against 0.0141N silver nitrate solution taken in the burette.during titration silver chloride precipitate will form.the end point is light brick red colour.

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STANDARDIZATION OF 0.0141N AgNO3:

We preparing  the Silver nitrate solution that is not the correct Normality for sometimes.Normality may differ by various factors like temperature,time,etc.to know the exact normality of silver nitrate solution,we have to do standarization.the procedure of standardization is same as told earlier.but we using here standard sodium chloride solution instead of sample.take two clean conicle flasks,pour 10 ml of standard sodium chloride solution and 4 drops of potassium chromate indicator.titrate against 0.0141N silver nitrate solution and note the volume.

Calculation of standardization:

                V1×N1/V2 = N2

V1 = Volume of sodium chloride solution (10ml)

V2 =  Volume of 0.0141N silver nitrate consumed.

N1 = Standard normality of silver  nitrate(0.0141)

N2 = The exact normality of present time.

Example:

 

Burette reading of 0.0141N silver nitrate solution is 10.1ml for 10ml sodium chloride solution taken.so the Normality will be

           10.0 × 0.0141 /  10.1 = 0.0139N

SAMPLE CALCULATION:

Cl = (V2-V1) × N × 35.45 × 1000 / Sv 

V1 = Initial reading of burette.

V2 = Final reading of burette.

N = Normality of silver nitrate solution from standardization. 

35.45 = Atomic weight of chloride.

1000 = For milligram conversion

Sv = Sample volume.

Model calculation:

Cl = (6.7-0) × 0.0141 × 35.45 × 1000 / 100 = 33.48mg/l.

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