Chem master's help needed..

Test Preparation
1

<p>Zumdahl Chemistry, Pg.238 #114 (Challenge Problem)</p>

<p>A mixture of chromium and zinc weighing 0.362 g was reacted with an excess of hydrochloric acid. After all the metals in the mixture reacted, 225 mL of dry hydrogen gas was collected at 27 degree Celcius and 750. torr. Determine the mass percent Zn in the metal sample. [Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas; chromium reacts with hydrochloric acid to produce chromium (III) chloride and hydrogen gas.]</p>

<p>I got 65% but I think I'm wrong and am not sure how I got it.
Thanks for the help.</p>

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<p>anyone please help?</p>

3

<p>What is torr.?</p>

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<p>Hey our AP Chem classes are on the exact same chapter! Wish I could help you, but I've been lagging the homework.</p>

5

<p>torr = a measure of atmosphereic pressure
I believe 760 torr = 1 atm</p>

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<p>Oh we're just ending with basic stoichiometry in AP Chem. We didn't incorporate atmospheric pressure, yet.</p>

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<p>so i guess no help?</p>

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<p>Is the answer 29.0%?</p>

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<p>Well maybe you don't know what the correct answer is, but the general method is to let the number of moles of Zn be x and Cr be y. So you have (molar mass of Zn)<em>x + (molar mass of Cr)</em>y = 0.362 and x + 2/3*y = 0.00902 (this number comes from solving for n, the number of moles of hydrogen, in the ideal gas law). the 1 and 2/3 comes from the moles of H2 produced in the respective reaction.</p>