13 g of an unknown metal powder form 19.4 g of sulphide. Determine the sulfide formula.

Let the valence of the unknown metal M be equal to 1.

Then the reaction equation for the formation of sulfide in general form:

2M + S = M2S

According to the reaction equation:

v (M) = m (M) / M (M) = 13 / M (M),

v (M2S) = m (M2S) / M (M2S) = 19.4 / (2M (M) + 32),

v (M) / 2 = v (M2S),

(13 / M (M)) / 2 = 19.4 / (2M (M) + 32),

whence we find M (M) = 32.5. There is no such metal.

Example valence of an unknown metal 2.

Then the reaction equation for the formation of sulfide in general form:

M + S = MS

According to the reaction equation:

v (M) = m (M) / M (M) = 13 / M (M),

v (MS) = m (MS) / M (MS) = 19.4 / (M (M) + 32),

v (M) = v (MS),

13 / M (M) = 19.4 / (M (M) + 32),

whence we find M (M) = 65, which corresponds to the metal zinc (Zn).