Question

Question #194d5

Answer 1

The empirical form is determinated experimentally by elemental analysis, and gives the proportion between the elements in the analysed compound. May be or not equal to the chemical formula.

Explanation:

The empirical formula is the formula we obtain directly from an elemental analysis.

Imagine that we know, that a compound has just carbon, nitrogen and hydrogen, and the elemental analysis gives 40% for carbon, 13.3% for hydrogen and 46.7% for nitrogen.

The empirical formula can be calculated like this:

In 100 g of that compound we would have:

40g (C), 13.3g (H), 46.7g (N)

The we convert the masses in to moles by dividing by the relative atomic masses of the elements (the number are not integer, but are pretty close)

`40/12` mol (C), `13.3/1` mol (H), `46.7/14` mol (N)

3.33 mol (C), 13.3 mol (H) , 3.33 mol (N)

Now we must convert the result into proportion of integers. Most times, divinding by the smaller number gives the required proportion, or gives us an ensight of we can do to reach it:

in this case, we get:

1 mol (C) , 4 mol (H), 1 mol (N), and the empirical formula is then

`CH4N` (I don't know how to put the numbers in index).

This is only the proportion of elements. The real proportion of the elements in the formula can be a multiple of that. In this case `CH4N` is an impossible formula and only the double
double `C2H8N2` can be a real molecular formula.