A materials scientist has created an alloy containing aluminum, copper, and zinc
ID: 980579 • Letter: A
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 12.561 g sample of the alloy and reacts it with concentrated HCl. T zinc chloride in addition to producing hydrogen gas. The copper does not react with the HCI. Upon completion of the reaction, a total of 10.6 L of hydrogen gas was collected at a pressure of 736 torr and a temperature of 27.0% C. Additionally, 2.769 g of unreacted copper is recovered he reaction converts all of the aluminum and zinc in the alloy to aluminum chloride and 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 %AlExplanation / Answer
Total mass = 12.561 g
mass of Cu = 2.769 g
Mass of Zn and Al = 12.561 - 2.769 = 9.792 g
let mass of Zn be m g
Then mass of Al = (9.792 - m) g
number of moles of Zn = mass / molar mass of Zn = m/65.38
number of moles of Al = mass / molar mass of Al = (9.792 - m)/26.98
For H2 gas:
P = 736 torr = 736/760 atm = 0.9684 atm
V=10.6 L
T = 27 oC = (273 + 27) K =300 K
use:
P*V = n*R*T
0.9684*10.6 = n*0.0821*300
n = 0.4178 mol
This is number of moles of H2 formed
Molar mass of H2 = 2 g/mol
mass of H2 gormed = molar mass * number of moles
= 2*0.4178
= 0.836 g <-----------------Answer
Zn + 2HCl ----> ZNCl2 + H2
1 mol of Zn forms 1 mol of H2
2Al + 6HCl ----> 2AlCl3 + 3H2
2 mol of Al forms 3 mol of H2
Total moles of Zn released = m/65.38 + (3/2)* (9.792 - m)/26.98
= 0.0153*m + 0.5444-0.556*m
= 0.5444 -0.5407*m
SO,
0.5444 -0.5407*m = 0.4178 moles
m = 0.234 g
So, mass of Zn = 0.234 g
Mass of Al = 9.792 - m = 9.792 - 0.234 = 9.558 g
Mass of Aluminium = 9.558 g <-------Answer
% cu = mass of Cu *100 / total mass
= 2.769*100/12.561
= 22.04%
%Al = mass of Al *100 / total mass
= 9.558*100/12.561
= 76.09%
%Zn = 100 - 22.04 - 76.09
= 1.87 %
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