Question

An alcohol is 68.84 % C and 4.962 % H by mass. The rest is oxygen. What is the empirical formula of the alcohol? Enter the elements in the order C, H, and then O.

Answer 1

The empirical formula is C₇H₆O₂.

Assume that you have 100 g of the compound.

Then you have 68.84 g C and 4.962 g H.

Mass of O = (100 – 68.84 – 4.962) g = 26.20 g O.

Now, we must convert these masses to moles and find their ratios.

From here on, I like to summarize the calculations in a table.

Element     Mass/g    Moles    Ratio     ×2   Integers  

     C           68.84      5.732    3.501  7.001       7

     H            4.962    4.923    3.006  6.012      6

     O          26.20      1.638     1          2             2

The empirical formula is C₇H₆O₂.