Ascientist is trying to discover information about an unknown metal in a compound. the formula for the compound is believed to be xbr3 where x is the unknown metal. the scientist determined that a 4.735 g sample of this compound contains 4.806×10−2 mol br . calculate the atomic mass of the unknown metal, x .

55.5 g/mol

Explanation:

When the compound dissociates it forms :

XBr₃  →  X⁺ + 3Br⁻

So, 1 mol of the metal is equivalent to 3 mol of Br.

1 mol of X 3 mol of Br

y                 4.806x10⁻² mol

By a simple direct three rule:

3y = 4.806x10⁻²

y = 1.602x10⁻²  mol of X

The mass of Br in the compound is the number of moles multiplied by its atomic mass, which is 80 g/mol

m = 80x4.806x10⁻² =

m = 3.845 g

So, the mass of the metal is the total mass less the Br mass (Lavoiser's law):

mX = 4.735 - 3.845

mX = 0.890 g

The atomic mass of X is the mass dividied by the number of moles:

M = 0.890/(1.602x10⁻² )

M = 55.5 g/mol