Hi i'm having trouble solving this question" if 7.54 grams of al reacts with excess of h2so4, and makes 0.33g of h2 . what is the % yield of h2gas produced?  

Answer is:  the % yield of hydrogen gas produced is 58.9%.
m(Al) = 7.54 g.
n(Al) = m(Al) ÷ M(Al).
n(Al) = 7.54 g ÷ 27 g7mol.
n(Al) = 0.28 mol; amount of substance.
From chemical reaction: n(Al) : n(H₂) = 1 : 1.
n(H₂) = 0.28 mol.
m(H₂) = 0.28 mol · 2 g/mol.
m(H₂) = 0.56 g.
%yield = 0.33 g ÷ 0.56 g · 100%.
%yield = 58.9%.