What does an empirical formula determine?

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What does an empirical formula determine?

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Answer 1 · 2016-10-10T09:51:19

The empirical formula is the simplest whole ratio that defines the proportions of elements in a species.

Explanation:

The molecular formula is always a mulitple of the empirical formula, and of course the multiple might be $1$ $1$ .

To illustrate this, the best real compounds to consider are the nitrogen oxides, $N O_{2}$ $NO_2$ , and $N_{2} O_{4}$ $N_2O_4$ . Clearly, these molecules both possess an empirical formula of $N O_{2}$ $NO_2$ (why?). But because of the lone electron on $N O_{2}$ $NO_2$ , the molecule can dimerize according to the following equation:

$2 N O_{2} (g) ⇌ N_{2} O_{4} (g)$ $2NO_2(g) rightleftharpoonsN_2O_4(g)$

i.e. $^{-} O (O =)^{+} N \cdot + \cdot N^{+} (= O) O^{-} ⇌$ $""^(-)O(O=)""^(+)N* + *N^(+)(=O)O^(-) rightleftharpoons$ $^{-} O (O =)^{+} N - N^{+} (= O) O^{-}$ $""^(-)O(O=)""^(+)N-N^(+)(=O)O^(-)$ .

To approach the molecular formula from the empirical formula, we need an estimate of the molecular mass of the molecule in $g \cdot m o l^{- 1}$ $g*mol^-1$ .

i.e. $Molecular formula$ $"Molecular formula"$ $=$ $=$ $(empirical formula) \times n$ $"(empirical formula)"xxn$

$n$ $n$ is a whole number to be determined.

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What does an empirical formula determine?

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