Question

4. A) The pH of a solution is changed from pH 6 to pH 10. Does this reflect an increase or decrease in [H+]?B) By how much has the [H+] changed?

Answer 1

As a solution loses H+ ions its pH increases, i.e. the solution becomes more basic.

In this case, the solution goes from an acidic pH of 6 to a basic pH equal to 10, this means that the concentration of H+ in the solution decreases.

Now, to determine how much is the change of concentration we can apply the following formula:

$\begin{gathered} pH=-\log \lbrack H^+\rbrack \\ -pH=\log \lbrack H^+\rbrack \end{gathered}$

We can clear the H+ concentration by applying the logarithm rules. We have a base 10 logarithm so when clearing we will have:

$\lbrack H^+\rbrack=10^{-pH}$

Now we replace the values of each pH and we will have the H+ concentration in each case.

$\begin{gathered} \lbrack H^+\rbrack_{pH=6}=10^{-6} \\ \lbrack H^+\rbrack_{pH=10}=10^{-10} \end{gathered}$

Therefore, the concentration difference will be:

$\begin{gathered} \Delta\lbrack H^+\rbrack=\lbrack H^+\rbrack_{pH=6}-\lbrack H^+\rbrack_{pH=10} \\ \Delta\lbrack H^+\rbrack=9.999\times10^{-7} \end{gathered}$

The change of concentration will be 9.999x10^-7