1.84 g of a mixture of CaCO3 and MgCO3 was heated to a constant weight. The constant weight of the residue was found to be 0.96 g. calculate the percentage composition of the mixture.. (Ca=40,Mg=24,C=12,O=16)
A
CaCO3=54.34%,MgCO3=45.66%
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B
MgCO3=54.34%,CaCO3=45.66%
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C
CaCO3=45.11%,MgCO3=54.89%
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D
MgCO3=73.24%,CaCO3=26.76%
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Solution
The correct option is CCaCO3=45.11%,MgCO3=54.89% We have, CaCO3+MgCO3→CaO+MgO+CO2↑
Mass of calcium carbonate = x g Mass of magnesium carbonate = (1.84 - x) g Mass of calcium oxide = y g Mass of magnesium oxide = (0.96 - y)g
Applying POAC for Ca atoms,
Moles of Ca atoms in CaCO3 = moles of Ca atoms in CaO
1×moles of CaCO3=1× moles of CaO Molar masses of calcium carbonate and calcium oxide are 100 and 56, respectively x100=y56
Again applying POAC for Mg atoms,
Moles of Mg in MgCO3 = moles of Mg in MgO 1×Moles ofMgCO3=1× moles of MgO
The molar mass of magnesium carbonate and magnesium oxide are 84 and 40 respectively. 1.84−x84=0.96−y40
From eqn (i) and (ii), we get x = 0.83 g, y = 0.465 g %ofCaCO3=0.831.84×100=45.11%%ofMgCO3=54.89%