Molecular formula
Related Topics: Percent Composition, Empirical Formula
Once the ratio of atoms has been established through determining the empirical formula, you want to try to nut out the real formula, the molecular formula, the formula you are all already familiar with.
Example: In the previous example we saw that the compound had a ratio of 2 P to 5 O. Suppose by means fair or foul we determined that its molar mass was 248g mol-1. We could then find its molecular formula.
Solution: One mole of P2O5 contains:
2 mole of P
5 mole of O
|
1 mole of phosphorus is |
31g, so |
2 mole is |
62g |
|
1 mole of oxygen is |
16g, so |
5 mole is |
80g |
|
1 mole of P2O5 is |
|
|
142g |
284/142 = 2, so we must have twice as many atoms per molecule as supposed. This gives P4O10 as the molecular formula.
The molecular mass for the compound of carbon, oxygen and hydrogen in problem 4 is 60g mol-1. Find its molecular formula.
Related Topics: Percent Composition, Empirical Formula