Percent of Oxygen in a compound

Question

Calculate the percentage by mass of the indicated element in the following compounds:
(a) oxygen in C2H5COOH. 

(b) oxygen in HC6H7O6. 

(c) oxygen in sodium sulfate.

Answer 1

I'll do one for you...

oxygen in C2H5COOH.

3 x 12.01 = 36.03

6 x 1.01 = 6.06

2 x 16 = 32.00

Sum:74.09

32/74.09   x 100 = 43.19% oxygen in propanoic acid

 

You can do the rest, I bet.  Advice:  do these to practice the molar masses of various elements, an essential knowledge base for chem.