The zinc within a copper-plated penny dissolves in hydrochloric acid if the copp

Question

The zinc within a copper-plated penny dissolves in hydrochloric acid if the copper coating is filed down in several spots (so that the hydrochloric acid can reach the zinc). The reaction between the acid and the zinc 2H+(aq)+Zn(s)H2(g)+Zn2+(aq) .

When the zinc in a certain penny dissolves, the total volume of gas collected over water at 25 C is 0.947 L at a total pressure of 743 mmHg . (Vapor pressure of water is 23.78 mmHg at 25 C .)

What mass of hydrogen gas is collected? Please answer in appropriate significant figures       

Explanation / Answer

2H+(aq) + Zn(s) H2(g) + Zn2+(aq)

pressure = 743 - 23.78 = 719.22 mm og Hg

Pressure = (719.22 / 760) = 0.9463 atm

PV = nRT

0.9463 * 0.947 = n * 0.0821 * 298

n = 0.03662 moles

mass of H2 = 0.03662 * 2 = 0.07324 g

mass of H2 = 0.0732 g to three significants

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