To find the mass of Cl₂, you need to (1) convert moles HCl to moles Cl₂ (via the mole-to-mole ratio from equation coefficients) and then (2) convert moles Cl₂ to grams (via the molar mass). It is important to arrange the conversions/ratios in a way that allows for the cancellation of units. The final answer should have 3 significant figures like the given value.
4 HCl(g) + O₂(g) -----> 2 Cl₂(g) + 2 H₂O(g) ^ ^
Molar Mass (Cl₂): 2(35.453 g/mol)
Molar Mass (Cl₂): 70.906 g/mol
0.125 moles HCl 2 moles Cl₂ 70.906 g -------------------------- x ---------------------- x ------------------- = 4.43 g Cl₂ 4 moles HCl 1 mole
