Question

5.50g of a certain Compound X, known to be made of carbon, hydrogen and perhaps oxygen, and to have a molecular molar mass of 136./gmol, is burned completely in excess oxygen, and the mass of the products carefully measured: product mass carbon dioxide 14.24g water 2.91g Use this information to find the molecular formula of X.

Answer 1

Answer:

The molecular formula is C8H8O2

Explanation:

Step 1: Data given

Mass of compound X = 5.50 grams

Mass of CO2 = 14.24 grams

Molar mass of CO2 = 44.01 g/mol

Mass of H2O = 2.91 grams

Molar mass H2O = 18.02 g/mol

Molar mass C = 12.01 g/mol

Molar mass O = 16.0 g/mol

Molar mass H = 1.01 g/mol

Molar mass of the compound = 136 g/mol

Step 2: Calculate moles CO2

Moles CO2 = 14.24 grams / 44.01 g/mol

Moles CO2 = 0.324 moles

Step 3: Calculate moles C

For 1 mol cO2 we have 1 mol C

For 0.324 moles CO2 we have 0.324 moles C

Step 4: Calculate mass C

Mass C = 0.324 moles * 12.01 g/mol

Mass C = 3.89 grams

Step 5: Calculate moles H2O

Moles H2O = 2.91 grams / 18.02 g/mol

Moles H2O = 0.161 moles

Step 6: Calculate moles H

For 1 mol H2O we have 2 moles H

For 0.161 moles H2O we have 2*0.161 = 0.322 moles H

Step 7: Calculate mass H

Mass H = 0.322 moles * 1.01 g/mol

Mass H = 0.325 grams

Step 8: Calculate mass O

Mass O = 5.50 grams - 3.89 grams - 0.325 grams

MAss O = 1.285 grams

Step 9: Calculate moles O

Moles O = 1.285 grams / 16.0 g/mol

Moles O = 0.0803 moles

Step 10: Calculate mol ratio

We divide by the smallest amount of moles

C: 0.324 moles / 0.0803 moles = 4

H: 0.322 moles / 0.0803 moles = 4

O: 0.0803 moles / 0.0803 moles = 1

The empirical formula is C4H4O

The molar mass of this empirical formula is 68 g/mol

Step 11: Calculate the molecular formula

We have to multiply the empirical formula by n

n = 136 g/mol / 68 g/mol

n = 2

We have to multiply the empirical formula by 2

Molecular formula = 2*(C4H4O) = C8H8O2

The molecular formula is C8H8O2