# chemistry

Hydrogen gas is produced when zinc reacts with hydrochloric acid. if the actual yeild of this reaction is 85%, how many grams of zinc are needed to produce 112L of H2 at STP?

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1. The reaction is:
Zn + 2HCl --> ZnCl2 + H2
1 mole of any gas at STP is 22.4 L
112L of H2 / 22.4 L/mol = 5 moles H2
(5 mol H2)(1 mol Zn / 1 mol H2) = 5 moles of Zn
The above relationship assumes that the reaction is 100% efficient. Since the reaction is only 85% efficient, MORE than 5 moles of Zn must be used. I will let you figure that part out on your own. [The multiplier you use has to do with the relationship of 100% to 85%]

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2. i don't get what to do next, can you please show me??

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3. multiply the 5 moles of zinc by the factor:
(1.00/0.85)

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4. then what do i do??

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5. 5 mols Zn x (100/85) = ?? mols Zn
You want grams, Convert mols Zn to grams by grams = mols x molar mass.

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6. 380

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