Question

20 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample?
a)60 b)84 c)75 d)96

Answer 1

Answer:

MgCO

3

→MgO+CO

2

The molar masses of MgCO

3

and MgO are 24+12+48=84 g/mol and 24+16=40 g/mol respectively.

Thus, 8 g MgO will be obtained from

40

84

×8=16.8 mg of MgCO

3

.

The percentage purity of magnesium carbonate in the sample is

20

16.8

×100=80%

Hence, the correct option is B

Answer 2

Answer:

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