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 12.921 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 10.5 L of hydrogen gas was collected at a pressure of 738 torr and a temperature of 27.0 °C. Additionally, 2.673 g of unreacted copper is recovered. Calculate the mass of hydrogen gas formed from the reaction.

also, Calculate the mass of aluminum in the alloy sample.

aswell as, What is the mass percent composition of the alloy? (for Cu, Al, and Zn)

please be detailed!

Answer 1

Mass of hydrogen gas

Using the ideal gas equation

PV = nRT

738/760 * 10.5 = n * 0.0821 * 300

n = 0.41396 moles

Molar mass of H2 gas = 2 gm/mol

Mass of hydrogen gas formed = 0.41396 moles * 2 gm/mol = 0.82793 moles

Mass of aluminium and zinc in sample = 12.921 - 2.673 = 10.248 gms

Let the mass of aluminium be x and mass of zn be (10.248-x)

x/27 * 3/2 + (10.248-x)/65.38 * 1 = 0.41396

x/18 + 0.1567 - 0.01529x = 0.41396

0.04026x = 0.25726

x = 6.3899 gms

Mass of zinc = 10.248 - 6.3899 = 3.8580

Mass percent of al = 6.3899/12.921 * 100 = 49.45%

mass percent of zinc = 3.8580/12.921 * 100 = 29.85%

mass percent of cu = 2.673/12.921 * 100 = 20.689%