The percentage composition of acetic acid is found to be 39.9% carbon, 6.7% hydrogen, and 53.4% oxygen, how would you determine the empirical formula of acetic acid?

1 Answer
Oct 26, 2015

Answer:

We assume #100* g# of compound. Therefore the acid contains #39.9* g* C#; #6.7* g* H#; and #53.4*g*O#.

Explanation:

We divide the percentage composition by the atomic mass of each constituent element:

#(39.9*g)/(12.011*g*mol^-1)= 3.32*mol#

#(6.7*g)/(1.0794*g*mol^-1)= 6.65*mol#

#(53.4*g)/(16.00 *g*mol^-1)= 3.34*mol#

We divide thru by the lowest quotient #(3.32)# to get #C:H:O-=1:2:1#.

So the empirical formula is #CH_2O#. And the empirical formula is the simplest whole number ratio that defines constituent atoms in a species.

Now it is a fact that the molecular formula of acetic acid is #H_3C-C(=O)OH = C_2H_4O_2#. Is this a mulitple of the empirical formula; i.e. what is #n# for #(CH_2O)_n = C_2H_4O_2#?