Question

A laboratory analysis of aspirin determined the following mass percent composition:

C 60.00% H 4.48% O 35.52% Find the empirical formula.

****I KNOW THE ANSWER FOR THIS IS C9H804, BUT I DO NOT UNDERSTAND WHY YOU MUTIPLY BY 4 AT THE END TO GET THERE. PLEASE THROUGHLY EXPLAIN THE STEPS AND WHY****

Answer 1

we have mass of each elements as:

C: 60 g

H: 4.48 g

O: 35.52 g

Divide by molar mass to get number of moles of each:

C: 60/12.01 = 4.995837

H: 4.48/1.008 = 4.444444

O: 35.52/16.0 = 2.22

Divide by smallest to get simplest whole number ratio:

C: 4.995837/2.22 = 2.25

H: 4.444444/2.22 = 2

O: 2.22/2.22 = 1

multiply all by 4:

C : 2.25*4 = 9

H:2*4 =8

O:1*4 = 4

So empirical formula is:

C9H8O4

You need to multiply by 4 so that all number becomes whole number.

Number of C is 2.25 . To make it a whole number, we multiply by 4