Solving mole calculations with equations

Question

Magnesium and hydrochloric acid react to form magnesium chloride and hydrogen gas. Calculate the volume of H₂ (g) produced at rtp when 4.8g Mg reacts with HCl. (Mg=24)

Answer 1

First, Karishma, you have to write out the balanced equation.

 

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

 

So 1 mole of Mg will produce 1 mole of H₂.  Since Mg has a molar mass of 24g,

 

4.8g x (1 mole/24g) = 0.20 mole Mg

 

So 0.20 mole of H₂ are produced.  At STP, 1 mole of any gas occupies 22.4 liters, so

 

0.20 mole x (22.4 liters/1 mole)

 

And you produce 4.48 liters of H₂. (4.5 liters using significant digits)