Find the empirical formula for each of the following:?

Question

a) 1.45 moles C, 2.91 moles H, 1.46 moles O

b) percent by mass : 11.11 % H, 88.89 % 0

c) 1.75 grams N, 500 grams O

Answer 1

a) 1.45 moles H

2.91 moles C

1.46 moles O

divide by the smallest number (1.45)

H: 1.

C: 2

O:1

The empirical formula is C2HO.

b. Let's say we have 100 grams of sample. Then there are 11.11 g of H and 88.89 g of O. Convert those to moles.

moles H = 11.11 / 1.01 = 11.0

moles O = 88.89 / 16.0 = 5.56

dividing by the smallest, H = 2, O = 1

The empirical formula is H2O.

c) 1.75 g N / 14.0 = 0.125 moles

.. .500 g O / 16.0 = 31.3 moles

Dividing by the smallest, N = 1, O = 250

The empirical formula is NO250!!!

Answer 2

a) You've got the ratio of moles. divide through by the smallest. sometimes when you do this (not in this case) you get a fraction; if that happens, multiply through to get rid of it.  Of course,0.99 is near enough to 1, because of experimental error.

b) pretend you have 100 g (all that matters is the ratio, so why not?).  Divide the masses of each element by the molar masses, and then proceed the same way as in (a). The answer should be very familiar to you.

c) Same way as (b), but I can't believe that these numbers are right.