Question

In the equation `Mg + 2HCl -> MgCl_2 + H_2`, what volume of hydrogen at STP is produced from the reaction of 50.0 g of `Mg` and the equivalent of 75 g of `HCl`?

Answer 1

`1.03` mol of dihydrogen gas will evolve, with a volume slightly over `22.4` `dm^3` at `STP`.

Explanation:

Moles of magnesium: `(50.0*g)/(24.31*g*mol^-1)` `=` `2.06` `mol`

Moles of hydrogen chloride gas: `(75.0*g)/(36.2*g*mol^-1)` `=` `2.07` `mol`

Given equimolar amounts, clearly, the gas is in deficiency as the stoichiometric equation requires 2 equiv of gas per equiv of metal.

So, the `1` mole of gas evolves, (conveniently, as at `STP` the molar volume is `22.4` `dm^3`).