Question

gA scientist is trying to discover information about an unknown metal in a compound. The formula for the compound is believed to be XBr3XBr3 where XX is the unknown metal. The scientist determined that a 4.700 g4.700 g sample of this compound contains 4.834×10−2 mol Br4.834×10−2 mol Br . Calculate the atomic mass of the unknown metal, XX .

Answer 1

It is given that :

The formula of the compound =
`$XBr_3$`

And that 4.70 g of the sample contains
`$4.834 * 10^(-2)$` mol of Br.

It means that :

1 mol of
`$XBr_3$` contains = 3 mol of Br

∴ 3 mol of
`$Br^-$` contain in 1 mol of
`$XBr_3$`

`$4.834 * 10^(-2)$` mol of
`$Br^-$` contains
`$1.576 * 10^(-2)$` mol of
`$XBr_3$`

Thus the mol of
`$XBr_3$` =
`$1.576 * 10^(-2)$` mol

The given mass is = 4.700 g

Therefore, the
`$\text{molar mass}$` of
`$XBr_3$`
`$=\frac{\text{mass}}{\text{mol}}$`

`$=(4.700 \ g)/(1.576 * 10^(-2) \ mol)$`

= 298.4 g/mol

So
`$\text{molar mass}$` of
`$XBr_3$` =
`$\text{molar mass}$` of X + 3 x
`$\text{molar mass}$` of Br

298.4 g/mol =
`$\text{molar mass}$` of X + 3 x 79.90 g/mol

298.4 g/mol =
`$\text{molar mass}$` of X + 239.7 g/mol

`$\text{molar mass}$` of X = 58.71 g/mol (since 1 amu = 1 g/mol)

Therefore the atomic mass of the unknown metal = 58.71 g/mol

So the unknown meta is Nickel.