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....

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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