Calculate the percentage by mass of calcium in a pure sample of calcium carbonate (\text{C… — JAMB UTME

Calculate the percentage by mass of calcium in a pure sample of calcium carbonate ( $\text{CaCO}_3$ ). $[\text{Ca} = 40, \text{C} = 12, \text{O} = 16]$

Answer: 40 %

Answer

The percentage by mass of calcium in calcium carbonate is 40%.

The molar mass of calcium carbonate (

\text{CaCO}_3

) is

100\text{ g/mol}

. Since one formula unit contains

40\text{ g}

of calcium, the percentage composition by mass of calcium is

\frac{40}{100} \times 100\% = 40\%

Step-by-Step Solution

Calculate the molar mass of calcium carbonate (

\text{CaCO}_3

Molar mass =

40 + 12 + (3 \times 16) = 100\text{ g/mol}

Sum the relative atomic masses of all constituent atoms in one formula unit of

\text{CaCO}_3

Determine the mass contribution of calcium in one mole of

\text{CaCO}_3

Mass of Ca =

40\text{ g}

Each formula unit of

\text{CaCO}_3

contains 1 atom of calcium.

Calculate the percentage composition of calcium.

Percentage of Ca =

\frac{40}{100} \times 100\% = 40\%

Divide the mass of calcium by the total molar mass of the compound and multiply by 100.

Key Concept

Percentage composition of an element in a compound

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