Question

How many moles of hydrogen gas can be evolved from the action of excess hydrochloric acid on a mass of `4.8*g` of magnesium metal?

Answer 1

Approx. `4.8*L`

Explanation:

We assess the following chemical reaction:

`Mg(s) + 2H_3O^(+) rarr Mg^(2+) + H_2(g) +2H_2O(l)`

And thus `"moles of metal"` `-=` `"moles of dihydrogen gas."`

`"Moles of metal"` `=` `"Mass"/"Molar mass"`

`=(4.8*g)/(24.3*g*mol^-1)=0.198*mol`.

And this `0.198*mol` `"dihydrogen gas is evolved"`.

The molar volume of an ideal gas under standard conditions is `24*dm^3`. (The definitions now vary across the different syllabuses, so I cannot be much help to you here). And so the volume of gas evolved is:

`0.198*molxx24*dm^3*mol^-1=??dm^3`.