Question

A sample of hard water contains 32 g of calcium carbonate in it. Calculate the number of calcium and carbonate ions present in the sample.

Answer 1

Mass of CaCO₃ = 32 g

Molar mass of CaCO₃:

40 + 12 + (3 × 16) = 100 g/mol

Number of moles:

`32/100` = 0.32 mol

Number of formula units:

0.32 × 6.022 × 10²³ = 1.927 × 10²³

CaCO₃ gives 1 Ca²⁺ ion and 1 \[\ce{CO^{2-}3}\] ion per formula unit.

Therefore:

Number of Ca²⁺ ions = 1.927 × 10²³​

Number of \[\ce{CO^{2-}3}\]​ ions = 1.927 × 10^23​