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 molar mass is 90 g/mol?

Answer 1

The molecular formula for lactic acid, given a percent composition and approximate molar mass, can be determined by first finding the empirical formula, which represents the simplest ratio of elements in the compound. In this case, the empirical formula is CH2O. To find the molecular formula, the molar mass of the empirical formula is divided into the approximate molar mass of lactic acid. The molecular formula for lactic acid is C3H6O3.

Step-by-step explanation:

The molecular formula for lactic acid can be determined using the percent composition and approximate molar mass. To calculate the molecular formula, we need to find the empirical formula first. The empirical formula shows the simplest ratio of the elements in a compound.

Step 1: Determine the moles of each element

We assume a 100 g sample of lactic acid, so we have 40.00 g of carbon, 6.71 g of hydrogen, and 53.29 g of oxygen. We can convert the mass of each element to moles using the molar mass.

moles of carbon = 40.00 g / 12.01 g/mol = 3.33 mol

moles of hydrogen = 6.71 g / 1.01 g/mol = 6.64 mol

moles of oxygen = 53.29 g / 16.00 g/mol = 3.33 mol

Step 2: Find the simplest ratio

We divide the moles of each element by the smallest number of moles to find the simplest ratio:

Carbon: 3.33 mol / 3.33 mol = 1

Hydrogen: 6.64 mol / 3.33 mol = 2

Oxygen: 3.33 mol / 3.33 mol = 1

Step 3: Write the empirical formula

The empirical formula for lactic acid is CH2O.

Step 4: Determine the molecular formula

We can find the molecular formula by calculating the ratio of the molar mass of the empirical formula to the molar mass of the molecular formula. The empirical formula mass of CH2O is 30 g/mol (12.01 g/mol x 1 + 1.01 g/mol x 2 + 16.00 g/mol x 1).

To find the molecular formula mass, we divide the approximate molar mass (90 g/mol) by the empirical formula mass: 90 g/mol / 30 g/mol = 3.

The molecular formula for lactic acid is therefore 3 times the empirical formula: C3H6O3.

Answer 2

C3H6O3

Step-by-step explanation:

To find the emperical of the compound,you divide the percentage composition of each element by it's molar mass(C=12, H=1, O=16).

For C,40/12=3.33. For H,6.71/1=6.71

For O,53.19/16=3.33.

Then divide everything by the smallest value which is 3.33

For C,3.33/3.33=1. For H,6.71/3.33=~2.

For O,3.33/3.33=1.

Emperical formula=CH2O

Molecular formula=(CH2O)n=90

(12+2*1+16)n=90

30n=90, n=3

molecular formula=(CH2O)3

molecular formula of lactic acid=C3H6O3.