4.2 g of Mg is burnt in 4.8 g of slushy to form magnesium sulphide.What is the limiting reagent? Calculate the amount of the reactions which remain unreached.

Explanation

`Mg + S to MgS`
No. of moles of magnesium = `(4.2)/24 = 0.175`
No. of moles of sulphur `= 4.8/24=0.15`
No. of moles of magnesium unreacted =0.175-0.15
=0.025
`therefore` Mass of magnesium unreacted = `0.025 xx 24 = 0.625 g`.
No. of moles of sulphur is loss, hence, it is a limiting reagent.