Heavy water is water in which the hydrogen atoms are replaced by the hydrogen isotope deut… — JAMB UTME

Heavy water is water in which the hydrogen atoms are replaced by the hydrogen isotope deuterium ( $^{2}_{1}\text{H}$ or $\text{D}$ ). Given that the atomic mass of deuterium is $2\text{ g mol}^{-1}$ and oxygen ( $^{16}_{8}\text{O}$ ) is $16\text{ g mol}^{-1}$ , what is the molar mass of heavy water ( $\text{D}_2\text{O}$ ) in $\text{g mol}^{-1}$ ?

Answer: 20 g mol^-1

Answer

The molar mass of heavy water (

\text{D}_2\text{O}

) is

20\text{ g mol}^{-1}

Heavy water (

\text{D}_2\text{O}

) contains two atoms of deuterium (

^2\text{H}

, atomic mass =

2

) and one atom of oxygen (

^{16}\text{O}

, atomic mass =

16

). The molar mass is calculated as

(2 \times 2) + 16 = 20\text{ g mol}^{-1}

Step-by-Step Solution

Determine the molecular composition of heavy water

Heavy water (

\text{D}_2\text{O}

) contains 2 deuterium atoms and 1 oxygen atom.

Deuterium is an isotope of hydrogen containing one proton and one neutron, giving it a mass number of 2.

Sum the relative atomic masses of all constituent atoms

(2 \times 2) + 16 = 20\text{ g mol}^{-1}

Multiplying the mass of deuterium by two and adding the mass of one oxygen atom yields the molar mass of the compound.

Key Concept

Heavy Water and Deuterium Molar Mass

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