Chapter 11.8, Problem 65PP

HCl reacts with magnesium metal to produce hydrogen gas.
   $2\text{HCl}\left(aq\right)\text{ + Mg}\left(s\right)\to {\text{ H}}_{\text{2}}\left(g\right){\text{ + MgCl}}_{\text{2}}(aq)$
a. What volume, in liters, of hydrogen at $\text{0 °C and 1}\text{.00 atm}$ (STP) is released when $\text{8}\text{.25 g of Mg}$ reacts?
b. How many grams of magnesium are needed to prepare $\text{5}{\text{.00 L of H}}_{\text{2}}\text{ at 735 mmHg and 18 °C}$ ?