Question

The $pH$ of a $10ml$ aqueous solution of $HCl$ is $4$. The amount of water to be added to this solution in order to change its $pH$ from $4$ to $5$ is?

• A. $30ml$
• B. $60ml$
• C. $90ml$
• D. $120ml$

Answer 1

Answer: (C)

$90ml$

$M_1{V}_1+M_2{V}_2=MxVx$

Where, $V_1\to$ Volume of the gicen $HCl$ solution $=10ml$

$M_1\to \left[H^{+}\right]$ion concentration in given $HCl$ solution $={10}^{-4}$

$V_2\to$Volume of water required

$M_2\to \left[H^{+}\right]$ion concentration in water $={10}^{-7}$

$Mx\to \left[H^{+}\right]$ion concentration required $={10}^{-5}$

$Vx\to$Total volume$=(10+V_2)$

$\therefore ({10}^{-4}\times 10)+({10}^{-7}\times V_2)={10}^{-5}(10+V_2)$

Solving, we get,

$V_2+90ml$