Question

After $20$ mL of $0.1M$ $Ba(OH{)}_2$ is mixed with $10$ mL of $0.2M$ $HCl{O}_4$, the concentration of $\stackrel{⊝}{O}H$ ions is :

• A. $2\times {10}^{-3}M$
• B. ${10}^{-3}M$
• C. $0.066M$
• D. $0.2M$

Answer 1

The correct option is C $0.066M$

Milliequivalents of $\stackrel{⊝}{O}H=20\times 0.1\times 2=4$ meq.
Milliequivalents of $HCl{O}_4(x=1)=10\times 0.2\times 1=2$ meq.
Milliequivalents of $\stackrel{⊝}{O}H$ left $=4-2=2$ meq.
Concentration or Normality of $\stackrel{⊝}{O}H=\frac{2}{30}$ $=0.066N$ of $\stackrel{⊝}{O}H$ $=0.066M$ of $\stackrel{⊝}{O}H$