# chemistry

posted by jeffrisa

A 0.052g sample of aluminium reacts with excess 6M HCL. A 48.3mL volume of hydrogen gas was collected over water at 22C and the pressure of the hydrogen gas was 751mmHg.calculate the aluminum percent purity in the sample.
What volume of hydrogen gas at STP is produced from the reaction of 0.044g of 98.0% pure aluminium with excess 6M HCl.

1. DrBob222

A.
2Al + 6HCl ==> 2AlCl3 + 3H2
Look up vapor pressure H2O @ 22 C = and I've estimated 22 mm
Use PV = nRT to solve for mols H2 evolved.
For P you have
Ptotal = pH2 + pH2O
751 mm = pH2 + 22
Therefore, estimated pH2 = 751-22 = approx 729. Use that for P in the PV = nRT formula.
Remember T must be in kelvin; solve for n.
Using the coefficients in the balanced equation, convert mols H2 to mols Al.
Then g Al = mols Al x atomic mass Al.

%Al = (grams Al from calcn/0.052)*100 = ?%

B.
This is just the reverse process from part A above. This should get you started.
mass Al = 0.044 x 0.98 = ?
Convert to mols H2 from the equation.
Convert mols H2 to volume remembering that 1 mol at STP occupies 22.4 L.

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