Question

Calculate pH of a solution whose $100$ml contains $0.2$g NaOH dissolved in it?

• A. $10.699$
• B. $11.699$
• C. $12.699$
• D. $13.699$

Answer 1

Answer: (C)

$12.699$

Concentration ( Molarity ) = $\frac{\text{moles of solute}}{\text{Volume of solution( in liters)}}$

Moles of solute = 0.2/40 = 0.005mol

Volume of solution = 100ml = 0.1 liters

$\therefore \left[O{H}^{-}\right]=\frac{n}{volume}=\frac{0.05}{0.1}=0.05M$

$pOH=-lo{g}_{10}\left[O{H}^{-}\right]=-log\left(0.05\right)$

pOH = 1.301

pH + pOH = 14

Hence, pH = 12.699