Question

Calculate pH of a solution of a mixture of 10 ml 0.1 M HCI and 40 ml 0.2 M HBr

• A. 0.68
• B. 0.56
• C. 0.74
• D. 0.72

Answer 1

The correct option is C 0.74

Both are very strong acids and we can assume almost complete dissociation
$\Rightarrow$ Milli equivalent of $H^{+}$ form HCI $=10\times 0.1=1$
Milli equivalent of $H^{+}$ from HBr $=40\times 0.2\times 1=8$
Total milli equivalent of $H^{+}$ in solution $=1+8=9$
$\therefore \left[4^{+}\right]=\frac{9}{50}=0.18$
$pH=-log\left[H^{+}\right]=0.74$