Chemistry 2001 JAMB Past Questions - Question 7: An oxide XO has a vapour density of 32. What is the atomic mass of X?

Correct Answer

A

Explanation

R.M.M. = 2 x V.D.XO2 = X +O2 = 2 X 32 = X +32X = 64 - 32 = 32
The vapor density of a substance (XO in this case) is the ratio of the mass of a certain volume of the substance to the mass of an equal volume of hydrogen gas under the same conditions. The molecular formula of water (H2O) is a common example where the vapor density is 18, which is the molecular weight of water divided by 2 (the number of moles of hydrogen in water).

The formula for vapor density (VD) is given by:

\[ VD = \frac{\text{Molecular Weight of Substance}}{2} \]

In your case, the vapor density (VD) is given as 32. Therefore:

\[ 32 = \frac{\text{Molecular Weight of XO}}{2} \]

To find the molecular weight of XO, you can rearrange the equation:

\[ \text{Molecular Weight of XO} = 32 \times 2 \]

\[ \text{Molecular Weight of XO} = 64 \]

The molecular weight of XO is 64. Since the molecular weight is the sum of the atomic masses of the constituent atoms, you need to find the atomic mass of X. If we assume that there is only one atom of X in the molecule, then the atomic mass of X would be 64.

However, keep in mind that there may be different possible molecular formulas for XO with different arrangements of atoms, so this is just one possible interpretation based on the given information.