Answer to Question #138773 in General Chemistry for Sammy

Question

During the experiment, Althea prepares a specific chemical to test on. The chemical has 56% C, 18%H, 32% O. a. Predict the Empirical formula b. If the amount of that compound being used is 120 g/mole, what will be its molecular formula?

Answer 1

Solution: 

a. Assume 100 g of sample:

$56g C×(1mol C)/(12.01115g C)$ = 4.66 mol C

$18g H×(1mol H)/(1.00797g H)$ = 17.86 mol H

 $32g O×(1mol O)/(15.99491g O)$ = 2.00 mol O

Since atoms combine in the same ratio that moles do, we divide all of the numbers of moles by the

smallest number to put everything into lowest terms:

C_4.66 H_17.86 O_2.00 → C_4.66/2.00 H_17.86/2.00 O_2.00/2.00  → C_2.33 H_8.93 O_1.00

If the mole ratio is not all whole numbers, we multiply through by the smallest integer which will

turn all of the numbers into integers. These numbers are the subscripts of the elements in the empirical

formula.

(C_2.33 H_8.93 O_1.00)₃ = C₇ H₂₇ O₃ (empirical formula)

Answer: C₇ H₂₇ O₃ (empirical formula)