1.

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

Answer» Correct Answer - B
`underset(84g)(MgCO_(3))overset(heat)(rarr)underset(40g)(MgO)+CO_(2)`
84 g of `MgCO_(3)` yield upon heating MgO = 40 g
20 g of `MgCO_(3)` yield upon heating `MgO=((40g)xx(20g))/((84g))`
`=9.52g`
Weight of MgO actually formed = 8.0g
% purity of `MgCO_(3)=((8.0g))/((9.52g))xx100=84%`.


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