a sample of chalk contains clay as impurity.The clay impurity losses 11% of its weight as moisture on prolong heating.

Question

a sample of chalk contains clay as impurity.The clay impurity losses 11% of its weight as moisture on prolong heating.5g sample of chalk on heating shows a loss in weight (due to evolution of co2 and water)by 1.1g. calculate % of chalk(caco3) in the sample.

Answer 1

Let the mass of chalk in the 5 g sample = y grams

Mass of clay in the sample = 5 g - y g = 5-y grams

Since 1 mole of CaCO₃ produces 1 mole of CO₂ and the molar mass of CO₂ = 44 g/mole and molar mass CaCO₃ = 100 g/mole, one can relate mass of CO₂ lost to the mass of chalk in the sample.  Thus,.....

Mass CO₂ lost = 44g/100g x y = 0.44y

Mass of water lost = (5-y)(0.11) = 0.55y

Total mass lost (as given in the question) = 1.1 g

Thus, we have 1.1 g = (0.55-0.11y) + 0.44y

0.33y = 1.1-0.55

y = 1.67 grams of chalk in the original sample

Percent chalk in original sample = 1.67 g/5 g (x100%) = 33.4%