Answer
20 ml.
Work Step by Step
1. Find the molar mass of ($NaOH$):
Na: 23
O: 16
H: 1
23 + 16 + 1 = 40g/mol
2. Calculate the nº of moles in 0.2g NaOH:
$mm = \frac{mass(g)}{n(moles)}$
$40 = \frac{0.2}{n(moles)}$
$n(moles) = \frac{0.2}{40}$
$n(moles) = 0.005$
3. Because the proportion is 2 $NaOH$ for 1 $H_2SO_4$:
$2NaOH + 1H_2SO_4$
$\frac{1}{2} = \frac{n(moles(H_2SO_4))}{0.005}$
$\frac{0.005}{2} = n(moles(H_2SO_4)) = 0.0025$
4. Find how much volume is needed.
$C = \frac{n(moles)}{V(L)}$
$0.125 = \frac{0.0025}{V(L)}$
$V(L) = \frac{0.0025}{0.125}$
$V(L) = 0.02L = 20ml$
