Question

Calcium Carbonate (CaCO3) contains 40% calcium , 12% carbon and 48 % oxygen by mass . Knowing that the law of constant proportions holds good , calculate the mass of the constituent elements in 2g of calcium carbonate .

Answer 1

According to law of definite proportions, in a chemical substance, the elements are always present in definite proportions by mass.
Given data:
Percentage of Ca present in CaCO3 – 40%
Percentage of C present in CaCO3  - 12%
Percentage of O present in CaCO3  - 48%
This means 100g of calcium carbonate contains 40g of Ca, 12g of C and 48g of O.
Similarly, 2g of Calcium carbonate contains 40% calcium , 12% carbon and 48 % oxygen by mass.
Let us find the masses of Ca, C and O present in 2g of CaCO3.
Mass of Calcium present in 2g of CaCO3 = 40/100 X2 = 0.8g
Mass of Carbon present in 2g of CaCO3 = 12/100 X 2 = 0.24g
Mass of Oxygen present in 2g of CaCO3 = 48/12 X 2 = 0.96g.

Answer 2

According to Law Of Definite Proportion or Law Of Constant Composition , A Chemical Compound is always made up of same elements combined together in same fixed proportion by mass .

Total Percent of Calcium Present in CaCO3 = 40%

Total Percent of Carbon Present in CaCO3 = 12%

Total Percent of Oxygen Present in CaCO3 = 48%

Now ;

Mass of Calcium Present in 2g of CaCO3

= 40

__ × 2 = 0.8g

100

Mass of Carbon Present in 2g of CaCO3

= 12

__ × 2 = 0.24g

100

Mass of Oxygen Present in 2g of CaCO3

= 48

__ × 2 = 0.96g

100

Therefore by the law of Constant Composition ,

• Mass of Calcium in 2g of CaCO3 0.8g ;
• Mass of Carbon in 2g of CaCO3 is 0.24g ;
• Mass of Oxygen in 2g of CaCO3 is 0.96g .

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