Question

A compound is found to contain 1.32 moles of Li, 0.66 moles of Se, and 2.64 moles of O. What is the empirical formula of the compound?

Answer 1

`Li_2SeO_4`

Explanation:

The empirical formula is the SIMPLEST whole number ratio that defines constituent atoms in a species. If we divide the given molar quantities, by the LEAST molar quantity (that of selenium), we get the empirical formula above.

`Li_2SeO_4` is clearly ionic, and non-molecular (`SeO_4^(2-)` is an analogue of the sulfate ion, `SO_4^(2-)`). Typically with these problems you are asked to provide the empirical formula, and then asked to provide the molecular formula given a molecular mass. The molecular formula is always a multiple of the empirical formula: `MF` `=` `(EF)_n`. Of course, the molecular formula might be the same as the empirical formula; in which case `n` `=` `??`