Question

The volume of water added to $500ml$, $0.5M$ $NaOH$ solution so that its strength becomes $10mgNaOHperml$ :

• A. $100ml$
• B. $200ml$
• C. $250ml$
• D. $500ml$

Answer 1

The correct option is D $500ml$

Suppose $x$ mole of water be added

no. of mole of $NAOH$ initially $=500\times 09.5\times {10}^{-3}$

$=0.25mole$

Mass of $NaOH=0.25\times 40$

$=10g$

Strength $=\frac{10}{500+x}$ (After addition of water)

$\frac{10}{500+x}=10mg\times {10}^{-3}g$

$1=0.5+{10}^{-3}g$

$0.5={10}^{-3}x$

$x=500ml$.