Solution :
It is given that :
The formula of the compound =
And that 4.70 g of the sample contains mol of Br.
It means that :
1 mol of contains = 3 mol of Br
∴ 3 mol of contain in 1 mol of
mol of contains mol of
Thus the mol of = mol
The given mass is = 4.700 g
Therefore, the of
= 298.4 g/mol
So of = of X + 3 x of Br
298.4 g/mol = of X + 3 x 79.90 g/mol
298.4 g/mol = of X + 239.7 g/mol
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.