20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (At. wt. of Mg = 24)

Options

A. 96
B. 60
C. 84
D. 75

Answer

C

Explanation

`underset(84g)(MgCO_(3(s))) overset(Delta)to underst(40g)(MgO_(s))) + CO_(2(g))`
84g of `MgCO_3 -= ` 40 g of `MgO`
`:.` 20 g of `MgCO_3 = (40)/(84) xx 20 = 9.52g ` of MgO
Actual yield = 8g of MgO
`:.` % Purity`=(8)/(9.52) xx 100 = 84%`