200cm³ of 0.50mol/dm³ solution of calcium hydrogen trioxocarbonate (IV) is heated. The maximum weight of solid precipitated is?

A. 10g
B. 25g
C. 20g
D. 15g

Correct Answer:

Option A – 10g

Explanation

Equation: Ca(HCO3)2 → CaCO3 (precipitate) + H2O + CO2 (in the presence of heat)

V = 200 cm³ = 0.2 dm³

C = 0.5 mol/dm³ = 0.5M

N = CV ⟹
N = 0.5 × 0.2 = 0.1 mole

From the equation 1 mole of Ca(HCO3)2 gives 100g of CaCO3

(1 mole CaCO3 = 40 + 12 + (3 x 16) = 100g/m)

0.1 mole of Ca(HCO3)2 gives xg of CaCO3

1/0.10=100/x

x=100×0.10=10g