Question

An unknown metal sulfate is found to be 72.07% SO4 2- by mass. Assuming that the charge on the metal cation is +3, determine the identity of the cation.

Answer 1

lets name the unknown metal as M. Cation would be M³⁺.
the molecular formula of the compound is M₂(SO₄)₃
the mass of one mole - (molar mass of M x2 + 3 x molar mass of SO₄²⁻)
                                   = 2M + 96 x 3
                                   = 2M + 288
In 1 mol if there's 72.07% of sulphate , 
then 72.07 % corresponds to 288 g
               1 % is then      - 288/72.07 
       100 %  of the compound - 288/72.07 x 100 
 molar mass of the compound - 399.6 g/mol
mass of 2M - 399.6 - 288 = 111.6 g
molar mass of M - 111.6 /2 = 55.8 g/mol
the element with molar mass of 55.8 is Fe.
Unknown metal is iron(III) , Fe³⁺

Answer 2

The charge on the metal cation is +3, the identity of the cation is Iron, Fe.

What are metals?

A metal is a lustrous and polished material that is a good conductor of electricity.

Assume the unknown metal be x

The cation would be x³+

The molecular formula of the compound will be x₂(SO₄)₃

The mass of one mole = molar mass of x + 3x molar mass of SO₄²⁻

2x + 96 × 3

2x + 288

The molar mass of the compound is 399.6 g/mol

Mass of 2x - 399.6 - 288 = 111.6 g

The molar mass of x is 111.6

$\dfrac{111.6}{2} = 55.8 g/mol$

The element whose molar mass is 55.8 is Fe iron.

Thus, the element is iron, Fe.

Learn more about metals

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