Answer to Question #93474 in General Chemistry for Brooke

Question

Adipic acid is an inorganic compound composed of 49.31% C, 43.79% O, and the test hydrogen. If the molar mass of adipic acid is 146.1 g/mol, what are the empirical and molecular formulas of adipic acid?

(I’ve already got most of the work done. I just don’t know how to get the empirical mass.)

Answer 1

Let 100g of adipic acid is taken

Amount of C$=$ $49.31g$

Amount of O$=$ $43.79g$

Amount of H $=100-49.31-43.79=6.9g$

Moles of C$=\frac{49.31}{12.0079}=4.105 mole$ C

Moles of H =$\frac{6.9}{1.0079}=6.845mole$ H

Moles of O$=$ $\frac{43.79}{15.999}=2.737mole$ O

Find small, whole number ratio; divide all moles by 2.737

C: $\frac{4.105}{2.737}=$ 1.5 moles C

H: $\frac{6.845}{2.737}=$ 2.5 moles H

O: $\frac{2.737}{2.737}=$ 1 mole O

Multiply by 2 in all moles for getting whole numbers

We get,

3 moles C

5 moles H

2 moles O

Then empirical formula becomes,

$C_3H_5O_2$

Mass of empirical formula of adipic acid $=73$ $\frac{g}{mole}$

 the molar mass of adipic acid $=$ 146.1 $\frac{g}{mole}$

Molar mass is two times the empiricl formula

So,

Molecular formula of adipic acid is $C_6H_{10}O_4$