If the oxide contains 7.17 % o by mass, what is the identity of the metal?

Answer is: the identity of the metal is lead (Pb).

ω(O) = 7.17% ÷ 100%.

ω(O) = 0.0717; mass percentage of oxygen in the oxide.

If we take 100 grams of compound:

1) m(O) = ω(O) · 100 g.

m(O) = 0.0717 · 100 g.

m(O) = 7.17 g; mass of oxygen in the oxide.

n(O) = m(O) ÷ M(O).

n(O) = 7.17 g ÷ 16 g/mol,

n(O) = 0.448 mol; amount of oxygen.

2) m(M) = 100 g - 7.17 g.

m(M) = 92.83 g; mass of metal in the oxide.

n(O) = n(M) = 0.448 mol.

M(M) = m(M) ÷ n(M).

M(M) = 92.83 g ÷ 0.448 mol.

M(M) =207.20 g/mol; molar mass of the metal.