1.

A sample of water has a hardness expressed as 80 ppm of Ca^(2+) This sample is passed through an ion exchange column and the Ca^(2+) is replaced by H^(+).What is the pH of the water after it has been so treated ? [Atomic mass of Ca=40]

Answer»

3
2.7
5.4
2.4

Solution :`10^6` ml water CONTAINS 80 GM of `CA^(2+)=80/40` moles =2 moles of `Ca^(2+)=2xx2` moles of `H^+` ions
so `10^3` ml of `H_2O` will have =`4xx10^(-3)` moles of `H^+` ions
so pH=3-log 4=3-0.6=2.4


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