Gas Laws and stoichiometry

Question

Assume that 18.4 g of Al react with HCl according to the equation Al(s) + HCl(aq) −→ AlCl3(aq) + H2(g) at STP. How many moles of Al react? Remember to balance the equation first. Answer in units of mol. How many moles of H2 are produced? Answer in units of mol. How much H2 at STP is produced? Answer in units of L

Answer 1

This question tries to trick you, perhaps, with the order of the instructions. You don't need to balance the equation in order to calculate the first answer (moles of Al): just divide 18.4g by the atomic weight of the element Al (on your periodic table). THEN you do need to balance the equation, in order of elements: Al, Cl, H (requires multiplying certain coefficients by 2 in order to obtain an integer for H2!). Then you can scale your moles of Al into moles of H2 (using the ratio of coefficients of H2 and Al in the balanced equation), and then volume (knowing that 1 mole of any ideal gas takes up 22.414 L -- and H2 is fairly close to ideal).

Check on your balanced equation coefficients (after YOU calculate them!): 2, 6, 2, 3 in order.