# Homework Help: Help for Chem Problem,

1. Oct 24, 2007

### yaho8888

1. The problem statement, all variables and given/known data

0.2500 g sample of an Aℓ-Zn alloy reacts with HCℓ to form hydrogen gas:
Aℓ(s) + 3H+(aq) → Aℓ3+(aq) + 3/2H2(g)
Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
The hydrogen produced has a volume of 0.147 L at 25°C and 755 mm Hg. What is the
percentage of zinc in the alloy?

2. Relevant equations

PV=NRT

3. The attempt at a solution

Frist I start out finding the number of moles of Hydrogen gas produced by using PV=NRT
N=((.993atm)(.147L))/((.0821)(298K))= .00596 mol of H2
1mol of Al = 26.98g
1mol of Zn = 65.93g
now what should I do?

2. Oct 24, 2007

### chemisttree

Well, you know that the sum of the masses of aluminum and zinc is 0.250 g. Let x = mass of aluminum in the alloy and y = mass of zinc in the alloy.

x+y=0.250

but

y = 0.250 - x, so the mass of zinc in the alloy is 0.250 g - x

You also know the number of moles of aluminum in the sample of the alloy is x/26.98 and the number of moles of zinc is (0.250 - x)/65.93. Can you take it from there?

3. Oct 24, 2007

### yaho8888

I know about that but how do you calculate the mol of Zn by using .00596mol of H2 I found in the gas law.

4. Oct 24, 2007

### chemisttree

Do you know of a relationship between the number of moles of Al and the number of moles of H2 produced from it's treatment with HCl? Do you know of a relationship between the number of moles of Zn and the number of moles of H2 produced from it's treatment with HCl? If you add the hydrogen produced from Al to the hydrogen produced from Zn how much will you have?