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DETERMINATION OF SODIUM CHLORIDE (SALT) BY VOLHARD'S METHOD

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Sandy Ganesh

on 1 September 2013

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Transcript of DETERMINATION OF SODIUM CHLORIDE (SALT) BY VOLHARD'S METHOD

DETERMINATION OF SODIUM CHLORIDE (SALT) BY VOLHARD'S METHOD

For preservation
taste reasons




Amount of NaCl in sample %

= (V2 – V1) x N x 5.844
W

Where,
W = Weight of sample
V2 = Titer volume of blank (mL)
V1 = Titer volume of sample (mL)
1mL of 0.1 N KSCN is equivalent to
5.844 mg of NaCl


Normality of KSCN = N1 x V1
V2

Where,
N1 = Normality of AgNO3
V1 = Volume of AgNO3
V2 = Volume of KSCN


Nitric acid – To acidify the solution

AgNO3 – To precipitate chlorides

Chloroform – Covers the precipitate, separates it from water , makes it unable to dissolve

Ammonium ferric sulphate solution – As an indicator

Described by Jacob Volhard, a German chemist in 1874

Uses a back titration with potassium thiocyanate to determine the concentration of chloride ions in a solution

Useful where the titrations have to
be performed at low pH

Give advantage for halide analysis

Accurate and precise result

Easy detection of endpoint





Analyte is treated with the measured excess of Silver nitrate:
Cl- + Ag+ AgCl + Ag+ (excess)

The unreacted Silver ions are titrated with a standard solution of Thiocyanate ion,
using Fe (III) as indicator:

Ag+ + SCN- AgSCN

The first slight excess of Thiocyanate ion reacts with Fe3+ to form a dark red complex

Fe3+ + SCN-
FeSCN2+





DETERMINATION OF
PROCEDURE
Homogenise the sample
Weigh 2-10g of mix sample &
Shake for 30 seonds
Add 5mL of (1+1) nitric acid &
Dilute with D.I water to about 100mL

Add an excess amount of 0.1 N
AgNO3

Add 3mL of choloroform/nitrobenzene

Add 1 mL of ferric alum solution & Shake the content for 1 minute

Back titrate with 0.1N KSCN

BEFORE TITRATION
AFTER TITRATION
IN EXCESS
VOLHARD'S
METHOD
PRINCIPLE
CALCULATIONS
Recovery :

(Amount of NaCl in spike sample - Amount of NaCl in sample) x 100
Amount of NaCl added

ADVANTAGES
LIMITATIONS
CONCLUSION
The volhard’s method is a better method for determining the salt content in a sample .
Although,it takes extra time , the results are accurate and precise .
It is applicable for all kind of sample which contains salt.

Time consuming
Common two methods:
MOHR'S METHOD
VOLHARD'S METHOD
REFERENCES
Determination of Chloride ion concentration by Titration (Volhard's method)- University of Canterbury
AOAC Method 935.47
A Text Book of Quantitative Inorganic Analysis- Arthur I. Vogel
Full transcript