A materials scientist has created an alloy containing aluminum, copper, and zinc

Question

A materials scientist has created an alloy containing aluminum, copper, and zinc, and wants to determine the percent composition of the alloy. The scientist takes a 12.028 g sample of the alloy and reacts it with concentrated HCl. The reaction converts all of the aluminum and zinc in the alloy to aluminum chloride and zinc chloride in addition to producing hydrogen gas. The copper does not react with the HCl. Upon completion of the reaction, a total of 10.6 L of hydrogen gas was collected at a pressure of 96.6 kPa and a temperature of 27.0 °C. Additionally, 2.158 g of unreacted copper is recovered. Calculate the mass of hydrogen gas formed from the reaction.

Explanation / Answer

Given

Volume of H2 gas = 10.6 L

Pressure = 96.6 kPa = 0.9534 atm

Temperature = 27 C = 300 K

R = 0.08206 L.atm/mol.K

PV = nRT

0.9534 atm * 10.6 L = n * 0.08206 L.atm/mol.K * 300 K

n = 0.410 moles

Molar mass of H2 = 2 g/mol

mass of H2 gas = No. of moles * Molar mass = 0.410 mol * 2 g/mol = 0.821 g

Answer is 0.821 g of H2 gas

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