Materials scientist has created an alloy containing aluminum, copper, and zinc,

Question

Materials scientist has created an alloy containing aluminum, copper, and zinc, and wants to determine me percent composition of the alloy. The scientist takes a 12.589 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 HCI. Upon completion of the reaction, a total of 10.3 L of hydrogen gas was collected at a pressure of 729 torr and a temperature of 27.0 degree C. Additionally, 2.739 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?

Explanation / Answer

m = 12.589 g sample

V = 10.3 L of H2 gas, P = 729 torr adn T = 27°C = 300 K

m = 2.739 g of copper recovered

a)

mass of H2 in reaction

PV = nRT

n = PV/(RT) = 729*10.3/(62.32*300) = 0.4016 mol of H2

mass = mol*MW =0.4016*2 =0.8032 g of H2

b)

mass of Aluminiumn in sample..

Al(s) + 3HCl = AlCl3 + 3/2H2(g)

Zn(s) + 2HCl = ZnCl2 + H2(g)

total H2 = 1.5+1 = 2.5

from Al = 1.5/25 = 0.6

so..

mol of H2 from Al = 0.4016 *0.6 = 0.24096

mol of H2 from Zn =  0.4016 *0.4 = 0.16064

so..

mol of Al = 0.24096/1.5 = 0.16064 mol of Al

mol of Zn = 0.24096/1 =  0.24096 mol of Zn

mass of Al = mol*MW = 0.16064 *26.981539 = 4.33431 g of Al

C)

for Cu = 2.739/12.589*100 = 21.7570 %

for Al = 4.33431 /12.589*100 = 34.42%

for Zn =100 - 21.7570 -34.42 = 43.8 %

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