1.

The K_a value for HCN is 10^-9. What is the pH of 0.4 M HCN solution?

Answer»

SOLUTION :`K_a=10^-9`
`C=0.4M`
`pH=-log[H^+]`
`[H^+]=SQRT(K_a TIMES c)`
`[H^+]=sqrt(10^-9 times0.4)`
`[H^+]=2 times10^-5`
`thereforepH=-log(2 times10^-5)`
`=-log2-log(10^-5)`
`=-0.3010+5`
`pH=4.699`


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