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?

Answer 1

Answer:

The mass of hydrogen gas is collected is 0.073 grams.

Explanation:

$2H^+(aq)+Zn(s)\rightarrow H_2(g)+Zn^{2+}(aq)$

Volume of gas collected = V = 0.947 L

Temperature of the gas ,T= 25°C = 298.15 K

Total pressure of pressure of the gas = 743 mmHg

Vapor pressure of the water = 23.78 mmHg

Pressure of the gas = 743 mmHg - 23.78 mmHg =719.22 mmHg=0.9463 atm

1 atm = 760 mmHg

Moles of hydrogen gas = n

Using an ideal gas equation:

$PV=nRT$

$n=\frac{PV}{RT}$

$n=\frac{0.9463 atm\times 0.947 L}{0.0821 atm L/mol K\tmes 298.15 K}$

n = 0.03661 mol

Mass of 0.03661 moles of hydrogen gas = 0.03661 mol × 2 g/mol= 0.073 g