Question

what mass in grams of hydrogen gas is produced if 20 mol of Zn are added to exvess hydrochloric acid according to the equation Zn(s)+2HCl(aq)-->ZnCl2(aq)+H2(g)

Answer 1

Use fencing & dimensional analysis to figure out your answer. I like to write the amounts given in the question under the chemical reaction and "swing" my way across to determine the answer.

Zn(s)+2HCl(aq)-->ZnCl2(aq)+H2(g)
20mols

Answer 2

Sorry that wasn't finished ...

Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)
20mols excess Xg


By the way, the letters in subscripts are the phase the matter is in. So Zinc will be a solid (s), hydrochloric acid will be in aqueous phase (aq), zinc chloride will be in aqueous phase (aq), and hydrogen will be a gas (g). These phases are determined by rules of solubility.

Back on track - so I will not give you the answer, but I'll solve for a similar problem.

How many grams of water is produced when mixed with 4.00g of oxygen gas and excess ammonia?

4 NH3(g) + 5 O2(g) --> 4 NO(g) + 6 H2O(g)
excess 4.00g Xg

Xg = grams of water produced
molecular weight of O2 = 32grams (16gx2)
molecular weight of water = 18grams (16 + (1x2))

4.00g O2 x 1mole O2 / 32 grams O2 x 6 mole H20 / 5 mole O2 x
18 grams H2O / 1 mole H2O = 2.7grams water produced

I used the molecular weight conversion factor and the mole ratio of oxygen gas to water, as seen in the equation, to figure out my answer.

Try this concept out with your chemical reaction to get the answer! What did you get?

Answer 3

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