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 10.624 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 8.47 L of hydrogen gas was collected at a pressure of 741 torr and a temperature of 27.0 °C. Additionally, 2.220 g of unreacted copper is recovered.

Calculate the mass of hydrogen gas formed from the reaction.

Calculate the mass of aluminum in the alloy sample.

What is the mass percent composition of the alloy?

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 10.624 g sample of the alloy and reacts it with concentrated HCI. 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 8.47 L of hydrogen gas was collected at a pressure of 741 torr and a temperature of 27.0 °C. Additionally, 2.220 g of unreacted copper is recovered Calculate the mass of hydrogen gas formed from the reaction Number Calculate the mass of aluminum in the alloy sample Number What is the mass percent composition of the alloy? Number Number Number Cu Al Zn

Explanation / Answer

First write and balance the overall reaction:

Al + Zn + 5HCl --------> AlCl3 + ZnCl2 + 5/2H2

Using PV = nRT we can determine the moles of H2 and then the mass:

n = PV/RT

n = (741/760) * 8.47 / 0.082 * (27+273)

n = 0.3357 moles of H2

m = 0.3357 moles * 2 g/mol = 0.6714 g

Looking the overall reaction, we can see that 5/2 moles of H2 are produced when 1 mol of Al or 1 mol of Zn react so:

moles of Al = 0.3357 * 2/5 = 0.1343 moles

m Al = 0.1343 moles * 26.98 g/mol = 3.6234 g of Al

If the total is 10.624 g, then:

mZn = 10.624 - 3.6234 - 2.20 = 4.8006 g

%Cu = 2.20 / 10.624 * 100 = 20.7078%

%Al = 3.6234 / 10.624 * 100 = 34.11%

%Zn = 4.8006 / 10.624 * 100 = 45.19%

Hope this helps.

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