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. Thé scientist takes a 11.573 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 9.04 L of hydrogen gas was collected at a pressure of 97.0 kPa and a temperature of 27.0 Additionally, 2.584 g of unreacted copper is recovered Calculate the mass of hydrogen gas formed from the reaction. Number 0.71 Calculate the mass of aluminum in the alloy sample. Number What is the mass percent composition of the alloy? Number Number Number 22.3 %Cu %, Al %Zn

Explanation / Answer

Mass of alloy containing aluminium, copper and zinc=11.573 gm

Mass of copper = 2.584

Mass of aluminium and zinc= 11.573-2.584=8.989 gm

Let x= mass of zinc , mass of aluminium= 8.989-x

Moles = mass/atomic weight

Atomic weights ( g/mole): Zn= 65.4 and that of aluminium = 27

Moles : Zinc =x/65.4 and aluminium= (8.989-x)/27

Moles of hydrogen collected (n) can be calculated from gas law equation

N= PV/RT, P= pressure in atm , 101.3 Kpa= 1atm, 97Kpa= 97/101.3 atm=0.96 atm, V= 9.04L, T= 27deg.c= 27+273= 300K, R= 0.0821 L.atm/mole.K, V= 9.04L

Hence n= PV/RT =0.96*9.04/(300*0.0821)=0.35 moles

Mass of hydrogen collected =moles* molar mass =0.35*2= 7 gm

The reaction of zinc and aluminium as

Zn+ 2HCl ----->ZnCl2+ H2 and Al+3HCl----->AlCl3+1.5H2

1 mole of zinc reacts with HCl to produce 1 mole of H2

x/65.4 mole of zinc produced x/65.4 moles of H2 and (8.989-x)/27 moles of Al produces 1.5*(8.989-x)/27 moles of H2

total moles of H2 produced = x/65.4+1.5*(8.989-x)/27= 0.35

0.0153x+0.056*(8.989-x)= 0.35

0.0153x+.5-0.056x= 0.35

X*(0.056-0.0153)= 0.5-0.35

Hence x= 3.69 gm, mass of Aluminium= 8.989-3.69=5.299 gm

Mass of zinc= 3.69gm, mass % of zinc = 100*3.69/11.573=31.88 and that of aluminium= 100*5.299/11.573=45.78

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