If cobalt metal is mixed with excess sulfur and heated strongly, a sulfide is
produced that contains 55.06% cobalt by mass. calculate the empirical
formula of the sulfide.

Co2S3.

Explanation:

% of sulphur =  44.94 %

Dividing by the atomic masses:

Co = 55.06 / 58.93 = 0.9343

S = 44.94 / 32.078 = 1.4010

Working out the ratio of Co to S:

1:1.5

= 2:3.

So the empirical formula is Co2S3.

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