Question

1g of Mg is burnt in a closed vessel which contains `0.5g of O_(2)`
(i) Which reactants is left in excess
(ii) Find the mass of the excess reactant.
A. `O_2` is a limiting reagent and Mg is in excess by 0.25 g.
B. Mg is a limiting reagent and is in excess by 0.5 g.
C. `O_2` is a limiting reagent and is in excess by 0.25 g.
D. `O_2` is a limiting reagent and Mg is in excess by 0.75 g.

Answer 1

`underset(2xx24)(2Mg)+underset(2xx16)(O_2) to underset(2(24+16))(2MgO)`
48g of Mg requires 32g of `O_2`
1 g of Mg requires `32/48` = 0.66g of `O_2`
Oxygen available = 0.5g
hence, `O_2` is limiting reagent.
32g of `O_2` reacts with 48 g of Mg
0.5 g of `O_2` will react with `48/32xx0.5=0.75g` of Mg
Exess of Mg = (1.0-0.75)=0.25g