Question

What is the pH of resulting solution when \(20\text{ mL }\frac{M}{10}\text{ NaOH}\) and \(10\text{ mL }\frac{M}{10}\text{ H}_2\text{SO}_4\) are mixed together ?

• A. \(0\)
• B. \(2\)
• C. \(7\)
• D. \(10\)

Hint:

Compare the moles of OH- with the moles of H+ before finding pH.

Answer 1

The Correct Option is C

Step 1: Equivalents method:
Normality of NaOH = 0.1 N, normality of $\text{H}_2\text{SO}_4$ = 0.2 N (n-factor 2).

Step 2: Compare:
Milliequivalents of base = $20\times 0.1 = 2$. Milliequivalents of acid = $10\times 0.2 = 2$.
They are equal, so the mixture is just $\text{Na}_2\text{SO}_4$ in water. Neither of its ions reacts with water, so the solution is neutral with pH = 7 (option C).

Final Answer:
pH of the mixture is 7. \[ \boxed{7} \]