Question

20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample ?
(At. Wt. : Mg = 24)
(1) 60 (2) 84
(3) 75 (4) 96

Answer 1

Answer:

MgCO3​→MgO+CO2​

The molar masses of MgCO3​ and MgO are 24+12+48=84 g/mol and 24+16=40 g/mol respectively.

Thus, 8 g MgO will be obtained from  4084​×8=16.8 mg of  MgCO3​.

The  percentage purity of magnesium carbonate in the sample is  2016.8​×100=80%

your answer should be 80 and not 84

Hence, the correct option is B

Explanation: