chemistry

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A common way of producing hydrogen gas in the lab is by reacting zinc with hydrochloric acid.
Zn (s) + 2 HCl (aq) -> ZnCl2 (aq) + H2 (g)
A sample of impure zinc, of mass 5.10g, reacted with an excess of hydrochloric acid solution 3.0 mol dm-3 concentration. In the end 1.7dm-3 of hydrogen was obtained. Calculate the percentage impurities in the zinc sample.

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What are the conditions? T, P? I will assume STP but technically this problem can't be worked without that informatiion.
1.7 dm-3 H2 produced. Convert to mols. That's 1.7 x (1 mol/22.4 dm-3) = ?
Convert to mols Zn. mols Zn = mols H2 (look at the coefficients in the balanced equation).
Then mols Zn x atomic mass Zn = grams Zn.
% Zn = (g Zn/5.10)*100 = ?
% impurities = 100-%Zn.

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