# What critical piece of information must be known (or given in the problem) in order to determine the molecular formula for a compound from its empirical compound?

Oct 6, 2016

The molecular mass of the compound is required to calculate the molecular formula from the empirical formula.

#### Explanation:

The $\text{empirical formula}$ is the simplest whole number ratio defining constituent atoms in a species. The $\text{molecular formula}$ is always a multiple of the $\text{empirical formula}$, and of course the multiple may be one. Without the molecular mass, we have no way of interrogating the molecular formula, even though we know that it is a multiple of the empirical formula. And thus,

$\text{molecular formula}$ $=$ $n \times \left\{\text{empirical formula}\right\}$

$n$ must be determined by some means.

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