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# Chemistry ?

A student prepares a sample of hydrogen gas (H2) by reacting zinc metal with hydrochloric acid. The reaction is shown in the equation below. The student collects 152 milliliters of hydrogen gas at 25o C and 758 torr. If the vapor pressure of water at this temperature is 28 torr, determine the following. You must show your complete calculation for each part for full credit.Zn (s) + 2 HCl (aq) —- ZnCl2 (aq) + H2 (g)

a) The partial pressure of hydrogen in the collection flask.

b) How many moles of hydrogen gas were collected?

c) How many grams of zinc metal were reacted

### 1 Answer

Relevance
• Zn (s) + 2 HCl (aq) —- ZnCl2 (aq) + H2 (g)

a) P total = PH2 + P H2O

758 torr = PH2 + 28 torr

PH2 = 758 - 28 = 730 torr

PH2 = 730 torr x 1 atm/760 torr = 0.96 atm

b) T = 25 degree C = 273 + 25 = 298 K

VH2 = 152 ml = 0.152 L

R = 0.08206 L*atm/mol-K

and PH2 = 0.96 atm

mol H2 = nH2 = PH2*VH2/RT

= 0.96 atm x 0.152L/0.08206 L*atm/mol-K x 298K

mol H2 = 5.97 x 10^-3 mol

mass of Zn = 5.97 x 10^-3 mol x 65.38g /mol = 0.33 grams

I hope this helps you!

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