Theory of acids and bases

pH of acids

Exercise 11

    

 

Find the $pH$ of a $7.6\cdot 10^{-4}\;M$ solution of $HNO_3$ ! First we write down the equation of it's dissociation. Is it..

a) $HNO_3 (aq)$ $NO_2^+ (aq)$ $+$ $OH^- (aq)$ b) $HNO_3 (aq)$ $+$ $OH^- (aq)$ $NO_3^- (aq)$ $+$ $H_2O(l)$ c) $HNO_3 (aq)$ $H^+ (aq)$ $+$ $NO_3^- (aq)$ d) $HNO_3 (aq)$ $+$ $H^+$ $NO_2^+ (aq)$ $+$ $H_2O(l) ?

c)$ HNO_3 (aq)$ $H^+ (aq)$ $+$ $NO_3^- (aq)$

This reaction is complète. True or false ?

True, more exactly: $HNO_3 (aq)$ $\longrightarrow$ $H^+ (aq)$ $+$ $ NO_3^- (aq)$

What would be $[H^+(aq)]$?

$[H^+(aq)]$ will have the same molar concentration than $HNO_3$, so: $[H^+(aq)]$ $=$ $7.6 \cdot 10^{-4}\;M$

Calculate the $pH$!

$pH$ $=$ $-log(7.6 \cdot 10^{-4})$ $=$ $3.12$