1. What is meant by hard water, what ions are responsible for making water hard?
ID: 492136 • Letter: 1
Question
1. What is meant by hard water, what ions are responsible for making water hard? 2. What is the purpose of adding 3 drops of potassium chromate to water sample before titration?1. What is meant by hard water, what ions are responsible for making water hard? 2. What is the purpose of adding 3 drops of potassium chromate to water sample before titration?
1. What is meant by hard water, what ions are responsible for making water hard? 2. What is the purpose of adding 3 drops of potassium chromate to water sample before titration?
Explanation / Answer
1.) Hard water doesn't give lather with soap. It is due to the presence bicarbonate, sulphate, chloride salts of Mg and Ca. The ions destroy the surfactant property of the soap. There are 2 types of hardness, temporary and permanant hardness. Temoprary hardness is caused due to bicarbonate salts of Mg, Ca. It can be removed using softner or boiling. By boiling the bicarbonates get precipitated as carbonates. Permanant hardness is caused due to sulphate and chloride salt of Mg and Ca. Can be removed using softener or ion-exchange column and not by boiling.
2.) It is used in Mohr's method used for estimating the concentration of chloride ions in water. The water is titrated against AgNO3. The chloride ions present get precipitated as AgCl. The indicator used in this method is potassium chromate. Excess AgNO3 reacts with potassium chromate to give a red-brown precipitate of silver chromate (Ag2CrO4). Thus potassium chromate is used as an indicator.
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