What is the pH of a buffer system that contains 0.170 M hydrocyanic acid (HCN) and 0.140 M sodium cyanide (NaCN)?

1 Answer
anor277
Jan 17, 2018

pH=9.13...

Explanation:

We use the [buffer equation....](https://socratic.org/questions/how-do-buffers-maintain-ph)

And here....

pH=pK_a+log_10{[[A^-]]/[[HA]]}

And so in this context....

pH=9.21+log_10{[[N-=C^-]]/[[HC-=N]]}

pH=9.21+underbrace(log_10{[[0.140*mol*L^-1]]/[[0.170*mol*L^-1]]})_(-0.084)=9.13.

AS always in these buffers, the pH moves in the direction of the more concentrated species....here the acid is more concentrated, and the pH decreases with respect to pK_a.

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