Question

$4.0g$ of $NaOH$ and $4.9g$ and $H_{2}S{O}_4$ are dissolved in water and volume is made upto $250ml$. The $pH$ of this solution is:

• A. $7.0$
• B. $1.0$
• C. $2.0$
• D. $12.0$

Answer 1

Answer: (A)

$7.0$

Given mass of $NaOH=4$ g

Molar mass of $NaOH=23+16+1=40$ g

Moles of NaOH$=\frac{4}{40}=0.1$

So OH moles$=0.1$

Molar mass of $H_{2}S{O}_4=2+32+16\times 4=98$g

Mass of $H_{2}S{O}_4=4.9$g

Moles of $H_{2}S{O}_4=\frac{4.9}{98}=0.05$

So moles of $H^{+}=2\times 0.05=0.1$(each $H_{2}S{O}_4$ gives 2$H^{+}ions$)

Moles of $H^{+}$ and $O{H}^{-}$is equal so they react and have pH equal to 7