Cracking the SAT Chemistry Subject Test

H 2 SO 4 sulfuric   acid    (only   the first   H   is  strong)

HClO 4 perchloric   acid

Strong  Bases

Group   1   hydroxides  such    as  LiOH,   NaOH,   KOH,    etc.

Calculating pH for Strong Acid or Base Solutions

We’ve said that strong acids and bases completely dissociate. This means that,
for strong acids, [H+] equals the [STRONG ACID], and for strong bases, [OH−]
equals the [STRONG BASE].

Example: What is the pH of 1.0 M HNO 3 (aq)?

Solution: First, write the balanced chemical equation.

HNO 3 (aq)  →   H+(aq)  +   NO 3 −(aq)

Second,  realize     that    there   is  really  no  HNO 3 (aq)  in

solution;    it  has     all     dissociated.    Therefore,  what    we

really  have    is

HNO 3 (aq)  →   H+(aq)  +   NO 3 −(aq)

1.0M                                                1.0 M                               1.0 M

Third,  since   pH  is  the −log[H+],   we  get

pH  =   −log[H+]

                    =   −log(1.0    M)

                    =   −log(10^0 M)

                    =   0                                                                                                                                                                   

It’s a good idea to remember that for a 1.0 M solution of any strong acid, pH = 0
because these solutions are commonly used in the SAT Chemistry Subject Test
laboratory questions. Don’t make the mistake of thinking that −log (1) = 1!

Example: What is the pH of 1.0 M KOH(aq)?

Solution: First, write the balanced chemical equation.