Answer
Solution $X$: $[H3O+]=1×10^{−9}M$
Solution $Y$: $[H3O+]=1×10^{−7}M$
Work Step by Step
1. Use the following equation to calculate the hydronium ion concentration on solution "X":
$[H3O+]=10^{−pH}$
$[H3O+]=10^{−9.0}$
$[H3O+]=1×10^{−9}M$
** There is only 1 digit after the decimal point in "9.0", therefore, the number of significant figures of the $[H_3O+]$ must be equal to 1.
2. Repeat the same process for solution "Y":
$[H3O+]=10^{−pH}$
$[H3O+]=10^{−7.0}$
$[H3O+]=1×10^{−7}M$
** There is only 1 digit after the decimal point in "7.0", therefore, the number of significant figures of the $[H_3O+]$ must be equal to 1.
