Determination of Chloride by mohr method lab: Why do you add NaHCO3 to the sampl

Question

Determination of Chloride by mohr method lab: Why do you add NaHCO3 to the sample solutions. Give the deleterious side reactions that occur if the solution is (a) too acidic (B) too basic Determination of Chloride by mohr method lab: Why do you add NaHCO3 to the sample solutions. Give the deleterious side reactions that occur if the solution is (a) too acidic (B) too basic Why do you add NaHCO3 to the sample solutions. Give the deleterious side reactions that occur if the solution is (a) too acidic (B) too basic

Explanation / Answer

1. In this method the chlorine was determined by by reacting with AgNO3. It will reacts with AgNO3 to form AgCl precipitate. the endpoint of the titration is found by adding chromate ion. After AgCl precipitate , the excess of AgNO3 reacts with chromate ion to form Ag2Cr2O7. which indicates redish brown colour as endpoint.

In this titration method NaHCO3is added to adjust pH in between 6-7.5.

When the pH goes below 7. the chromate ion protonated and the chromic acid form predominates in the solution. Consequently, in more acidic solutions the chromate ion concentration is too low to produce the precipitate at the equivalence point. If the pH is above 10, brownish silver hydroxide forms and masks the end point. A suitable pH was achieved by saturating the analyte solution with sodium hydrogen carbonate.

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