Answer
Approximately 7.65 ml.
Work Step by Step
1. Find $[H^+]$
$[H^+] = 10^{-pH}$
$[H^+] = 10^{-2.05} = 8.9125 \times 10^{-3}M$
2. Find the nº of moles of $H^+$ in the solution:
$n(moles) = C * V(L)$
$n(moles) = 8.9125 \times 10^{-3} * 10$
$n(moles) = 8.9125 \times 10^{-2}$
3. Since $HCl$ is a strong acid:
$n(moles)(H^+) = n(moles)(HCl)$
4. Convert that number to grams of $HCl$
$mm(HCl) = 1.01 + 35.45 = 36.46$
$mass(g) = n(moles) * mm$
$mass(g) = 8.9125 \times 10^{-2} * 36.46$
$mass(g) = 3.25g$
5. Since the initial solution is 36% HCl (mass), we will need;
$\frac{36}{100} = \frac{3.25g}{x}$
$36x = 325g$
$x = 9.03g$
6. Convert that mass to volume, using the density:
$V = \frac{mass}{density}$
$V = \frac{9.03}{1.18}$
$V = 7.65 ml$
