Question

2AL+6H-->2AL+3H.

What volume of hydrogen gas at STP would be evolved in a reaction of 36.0mg of 98% pure aluminum with the hydrogen being an ideal?

I got the ml of hydrogen, but I don't know how to work it with AL being 98%pure.

Answer 1

equation does not make sense as typed.
Perhaps:
2Al + 6 H+ ---> 2 Al+3 + 3 H2(gas)
The aluminum is 98 % pure
so we really have .98*36 =35.3 mg of Al
How many moles of Al is that?
Al is 27 grams/mol
so we have 35.3 *10^-3 g / 27 g/mol = 1.31 * 10^-3 mol of Al
I get 3 moles of H2 for every 2 moles of Al
so moles of H2 = (3/2)(1.31*10^-3) = 1.96 *10^-3 mol of H2
at STP an ideal gas is about 22.4 liters/ mole
so
1.96 *10^-3 mol * 22.4 L/mol = 43.9^10^-3 L = .0439 L = 43.9 mL

Answer 2

Thanks so much! Sorry about the equation, it was 3 H2.