Question

The pH of the solution obtained by mixing 100 ml of a solution of pH = 3 with 400 mL of a solution of pH = 4 is

• A. $3-log2.8$
• B. $7-log2.8$
• C. $4-log2.8$
• D. $5-log2.8$

Answer 1

The correct option is C $4-log2.8$

For pH = 3; $\left[H_3{O}^{+}\right]={10}^{-3}$
pH = 4; $\left[H_3{O}^{+}\right]={10}^{-4}$
Moles of $H_3{O}^{+}$ in 100 ml of solution pH $=3=\frac{{10}^{-3}}{1000}\times 100={10}^{-4}$
Moles of $H_3{O}^{+}$ in 400 ml of solution of pH $=4=\frac{{10}^{-4}}{1000}\times 400=4\times {10}^{-5}$
$\left[H_3{O}^{+}\right]=\frac{14\times {10}^{-5}\times 1000}{500}=2.8\times {10}^{-4}$
$pH=-log(2.8\times {10}^{-4})$
$=4-log2.8$