Question

The taste of sour milk is lactic acid. What is the molecular formula for lactic acid if the percent composition is 40.00% C, 6.71% H, 53.29% O, and the approximate molecular mass is 90 amu?

Answer 1

Answer:

$C_3H_6O_3$

Explanations:

Given the following parameters

Carbon = 40.0%

Hydrogen = 6.71%

Oxygen = 53.29%

Convert to mass

Carbon = 40.0grams

Hydrogen = 6.71grams

Oxygen = 53.29grams

Convert the mass to moles

Mole of carbon = 40.0/12 = 3.33moles

Mole of hydrogen = 6.71/1 = 6.71 moles

Mole of oxygen = 53.29/16 = 3.33moles

Divide by the lowest number of moles

Carbon: 3.33/3.33 = 1

Hydrogen: 6.71/3.33 = 2.01

Oxygen: 3.33/3.33 = 1

Determine the empirical formula

Empirical formula = CH2O

Determine the molecular formula

$\begin{gathered} (CH_2O)_n=90 \\ (12+2(1)+16)n=90 \\ 30n=90 \\ n=\frac{90}{30} \\ n=3 \end{gathered}$$(CH_2O)_3=C_3H_6O_3$

Hence the molecular mass of the compound is C3H6O3