Which of the following is closest to the mass of aluminium that must be added to excess HCl to produce 25.7L of hydrogen gas, at STP?

Question

A) 22.4g

B) 31g

C) 62g

D) 21g

Answer 1

Hi Eloise

First, you need, as usual, to find the balanced equation

2Al + 6 HCl --> 2 AlCl3 + 3H2 ..................Make sense?

This implies that 2 Moles of Al produce 3 moles of H2

And, one mole of gas occupies 22.4 liters at STP

Now you have all you need to solve the problem

25.7 L of H2 contains 25.7/22.4 = 1.15 moles

To produce that many moles, we need 1.15*2/3 moles of aluminum to produce it ==> .765 moles

.765 moles of Al ==> .765 * 26.98 gms AL/mole = 21.6 gm So, the answer is D