Question

When equal volumes of pH=4 and pH=6 are mixed together then the pH of the resulting solution will be: [log 5=0.7]

• A. $4.3$
• B. $4.7$
• C. $5$
• D. $5.3$

Answer 1

Answer: (A)

$4.3$

pH=4, pH=6

For pH=4, $\left[H^{+}\right]={10}^{-4}M$

For pH=6, $\left[H^{+}\right]={10}^{-6}M$

Molarity=$\frac{\text{no. of moles}}{\text{volume}}$

Let the volume be V.

No. of moles, $n_1={10}^{-4}\times V$

No. of moles, $n_2={10}^{-6}\times V$

Net number of moles after mixing = ${10}^{-4}\times V+{10}^{-6}\times V$

Net $\left[H^{+}\right]$ concentration = $\frac{{10}^{-4}\times V+{10}^{-6}\times V}{2V}$

pH = $-\log \left[H^{+}\right]$

pH = 4.3