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JAMB Chemistry 2024 Paper

Question : 2

Total: 138

The number of molecules of helium gas contained in 11.5g of the gas is

Solution:

Concept:

A fixed mass of a gas can be converted to moles using its molar mass, then moles are changed to molecules using Avogadro's number.

Explanation:

Helium gas has a molar mass of

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

Number of moles

= \frac{\text{mass}}{\text{molar mass}} = \frac{11.5}{4.0} = 2.875

moles.

Number of molecules

= \text{moles} \times \text{Avogadro's number}

Number of molecules

= 2.875 \times 6.02 \times 10^{23}

Number of molecules

= 1.73 \times 10^{24}

Answer:

1.73 \times 10^{24}

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