When aluminum is placed in concentrated hydrochloric acid, hydrogen gas is produced

When aluminum is placed in concentrated hydrochloric acid, hydrogen gas is produced. What volume of H2(g) is produced when 6.2g of Al(s) reacts at STP?

Answer:

the coefficients of this equation
2 Al (s) + 6 HCl (aq) -------> 2 AlCl3 (aq) + 3 H2 (g)

are in mole ratios. so all you need to do is
(1)… convert g Al to moles Al
(2)… use the coefficients to convert moles Al to moles H2
(3)… since this is at STP… use 22.41L = 1 mole @STP to convert moles H2 to L H2

and of course you should be using dimensional analysis
3.20g Al x (1 mole Al / 26.98g Al) x (3 moles H2 / 2 moles Al) x (22.41 L H2 / mole H2@STP) = 3.99L H2