1.

What is the pH value of 0.1(M) HCOOH solution if its ionisation constant, K_ is 1.78xx10^(-4) at 25^(@)C ? How much water is to be added to 1L of this solution so that the pH of the solution becomes double of its initial value?

Answer»

Solution :100 ML. 0.075 (M) Ca`(OH)_2`
`=2xx(0.075)/(1000)xx100-=0.015mol OH^-`
100 mL of 0.1(M) `HCL-=(0.1)/(1000)xx100-=0.1mol` of `H^+` ions
0.01 mol of `H^+` ions react completely with the same amount of `OH^-` ions and the solution contains (0.015-0.01) mol =0.005 mL of `OH^-` ions
`:.` In the solution `[OH^-]=(0.005)/(200)xx1000=0.025(M)`
`:.` POH of the solution `=-log_(10)(0.025)=1.6`
`:.` pH of the solution `=-log_(10)(0.025)=1.6`


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