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 11.684 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 HCI. Upon completion of the reaction, a total of 9.92 L of hydrogen gas was collected at a pressure of 735 torr and a temperature of 27.0 Additionally, 2.273 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 %Al %Zn

Explanation / Answer

a) PV=nRT

P=735 torr

V=9.92 L

T=27 degC = 300 K

R= 62 Ltorr K1mol1

Thus, n=0.392 mol

Mass of Hydrogen =2x.392= 0.784g

b) Copper left=2.273g

Al+Zn=11.684-2.273=9.411g

Al forms AlCl3 thus reacts with atleast 3eq of HCl

Zn forms ZnCl2 thus reacts with atleast 2eq of HCl

Ratio of Al:Zn=3:2

Mass of Al=5.65g

c) Mass of Zn=3.8g

Percentage compostion Cu= 19.5% Al=48.16% Zn=32.68% (decimals rounded off in certain places. For more accuracy consider all decimals)

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