Question

an HCI solution has a pH of 3.350. after some NaOH was added to it, the pH of the resulting solution became 6.780. what is the positive difference in concentration of [H3O+]?

Answer 1

Solution.

$pH=-log[H_3O^+];$ $[H_3O^+]=10^{-pH};$

If $pH=3.350;$

$[H_3O^+]=10^{-3.35}=4.467\sdot10^{-4}M;$

If $pH=6.780;$

$[H_3O^+]=10^{-6.78}=1.66\sdot10^{-7}M;$

$4.467\sdot10^{-4}-1.66\sdot10^{-7}=4467\sdot10^{-7}-1.66\sdot10^{-7}=4465.34\sdot10^{-7}=$

$=4.46534\sdot10^{-4}M;$

Answer: concentration $[H_3O^+]$ decreased by $4.46334\sdot10^{-4}M.$