Fructose is a type of sugar found in fruits and honey. Analysis of a 2.00-g
sample shows that it contains 0.80 g of C, 1.06 g of O, and 0.14 g of H. An independent
analysis shows that fructose has a molar mass of 180 g/mol. What is the molecular
formula for fructose?

The molecular formula is C6H12O6

Explanation:

Step 1: Data given

Mass of the sample fructose = 2.00 grams

Mass of C = 0.80 grams

Molar mass of C = 12.01 g/mol

Mass of O = 1.06 grams

Molar mass of O = 16.0 g/mol

Mass of H = 0.14 grams

Molar mass of H = 1.01 g/mol

Molar mass of the compound = 180 g/mol

Step 2: Calculate moles C

Moles C = 0.80 grams / 12.01 g/mol

Moles C = 0.067 moles

Step 3: Calculate moles O

Moles O = 1.06 grams / 16.0 g/mol

Moles O = 0.066 moles

Step 4: Calculate moles H

Moles H = 0.14 grams / 1.01 g/mol

Moles H = 0.139 moles

Step 5: Calculate the mol ratio

We divide by the smallest amount of moles

C: 0.067 moles : 0.066 moles = 1

O: 0.066 moles / 0.066 moles = 1

H: 0.139 moles / 0.066 moles = 2

For each C atom we have 1 O atom and 2 H atoms

The empirical formula is CH2O

The molar mass of this empirical formula is 30 g/mol

Step 6: Calculate the molecular formula of fructose

We have to multiply the empirical formula of CH2O by n

n = 180 g/mol / 30 g/mol

n = 6

The molecular formula = 6*(CH2O)

The molecular formula is C6H12O6

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