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Volhard Method of Chloride Determination

In this volhard method of chloride determination post we have briefly explained about principle, requirements, reagent preparation, volhard titration method procedure, calculation.

Volhard Method of Chloride Determination

A chloride blood test measures the amount of chloride in your blood. Chloride is a type of electrolyte. Electrolytes are minerals that are electrically charged that help control fluid quantity and the acid and body balance.

Often chloride is used to diagnose or monitor conditions such as renal disease, insecurity of the heart, liver disease and higher blood pressure, together with other electrolytes.

Principle

Volhard titration method uses the Volhard chloride estimation, protein being oxidized by the open Carius method using a solution of silver nitrate in concentrated nitric acid. The organic matter is destroyed and the chloride precipitated at the same the excess silver nitrate in then titrated with standard thiocyanate using ferric alum as the indicator.

Requirements

Materials

1. Test tube

2. Test tube stand

3. Glass burette

4. Conical Flasks

5. White tiles

Chemicals

1. Silver Nitrate

2. Nitric Acid

3. Ammonium Thiocyanate

4. Ammonium Ferric Sulfate

Reagents

1. 0.05 N Silver nitrate: Dissolve 0.895g of silver nitrate in about 2 ml of water and then make up to 100 ml with concentrated nitric acid. The solution keeps in a brown bottle for volhard titration method.

2. 0.02 N Thiyocyanate: 15.6 gm of Ammonium thiocyanate (NH4SCN) to a flask add 100 ml of water, and swirl to dissolve the NH4SCN. When solution is complete, filter through a hardened filter paper, or other suitable medium. Dilute the clear filtrate to 1 L with water and mix. Store the solution in a tightly stoppered glass bottle.

3. 5% Ferric alum: Dissolve 5gm of ammonium ferric sulfate in about 20 ml of water and then make up to 100 ml with double distilled water for volhard titration method.

Procedure

1. Pipette a sample in to clean dry conical flask and run it slowly with constant shaking, 3ml of silver nitrate solution.

2. Add 2 ml of concentrated nitric acid and heat over a Bunsen flame until digestion has occurred and the solution is pale Yellow in colour.

3. If the colour is deep yellow it can be discharged by adding a few drops of saturated potassium permanganate solution and warming again.

4. This should not be necessary with plasma. The digestion usually requires only one to two minutes.

5. When the digestion is completed, cool and add 6 ml of 5% ferric alum. Then titrated with 0.02N thiocyanate until a reddish brown colour persisting for ten to fifteen seconds is obtained.

6. To determine the standard add 2 ml of nitric acid and 6 ml of ferric alum solution to 3 ml of the silver nitrate solution, cool and titrate with 0.02N thiocyanate.

7. The difference between the two titration gives a measure of the amount of chloride in 1 ml serum and urine in terms of a 0.02 N solution in volhard titration method.

Calculation

Serum

Titration value of standard: ———– ml, B: Titre value of serum: ——————- ml

The amount of chloride in 100 ml of serum: (A –B) x 20 = ————- mg of chloride.

Urine

Titration value of standard: ———– ml, B: Titre value of urine: ——————- ml

The amount of chloride in 100 ml of urine: (A –B) x 20 = ————- mg of chloride.

Frequently Asked Questions on Volhard Titration Method

Why is Nitric acid used in the volhard titration method?

The volhard titration method is a back-titration developed to tackle this problem. For this process, using excess uniform silver nitrate, chlorides are precipitated to the solution. The silver nitrate that is used is created by the nitric acid reaction of silver foil.

What is the volhard titration method of analysis?

Volhard process for assessing chlorine, bromine, and iodine in the form of halides by precipitating them with excess silver nitrate and using a thiocyanate solution to titrate excess.

Which indicator is used in the volhard titration method?

The expression ‘excess’ is used because the moles of added silver nitrate are considered to surpass the moles of sodium chloride present in the sample so that all the present chloride ions react. The indicator Fe3+ (ferric ion) is then added, with the potassium thiocyanate solution titrated to the water.

Further Readings

Reference

Volhard Method of Chloride Determination