The mineral greenockite is a yellow sulfide of cadmium that is 78.0% cadmium and 22.0% sulfur. How do you determine the empirical formula of greenockite?

1 Answer
Dwight ยท Stefan V.
Dec 18, 2016

The empirical formula is CdS. The method is below.

Explanation:

Start by assuming a mass of 100 grams of the compound. Then, the percentages can be exchanged for masses.

i.e. there are 78 g of cadmium and 22 g of sulfur.

Convert each mass to moles:

Cd: 78 g112.4 g/mol=0.694 mol

S: 22 g32.06 g/mol=0.686 mol

To two digits, these values are equal, so the whole number ratio of mol (and therefore atoms) in the compound is 1:1.

The empirical formula is CdS

Note, if it is not obvious how to get a whole number ratio as above, the best way to proceed is to divide each number of moles by the smallest value. This should make it easier to get the ratio.

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