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

hydrochloric-acid

#1

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