Multiple Choice
The following results are obtained from burning 5 g of an organic molecule (MW = 233.07 g/mol), which contains C, H, and O, in a combustion chamber:
Determine the molecular formula of linolenic acid.
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3. Chemical Reactions
Combustion Apparatus
Multiple Choice
Combustion analysis of 0.326 g of a compound known to contain only C, H, and O produces 0.7160 g CO2 and 0.3909 g H2O. A mass spectrum indicates that this compound has a formula mass of 120 g/mol. What is the molecular formula?
A
C4H8O4
B
C3H8O
C
C3H4O
D
C6H16O2
E
The molecular formula cannot be determined from the information given.
Verified step by step guidance1
Determine the moles of carbon in the compound by using the mass of CO2 produced. Use the molar mass of CO2 (44.01 g/mol) to find the moles of CO2, and then use the ratio of moles of C to moles of CO2 (1:1) to find the moles of carbon.
Determine the moles of hydrogen in the compound by using the mass of H2O produced. Use the molar mass of H2O (18.02 g/mol) to find the moles of H2O, and then use the ratio of moles of H to moles of H2O (2:1) to find the moles of hydrogen.
Calculate the mass of carbon and hydrogen in the compound using their respective moles and atomic masses (C: 12.01 g/mol, H: 1.008 g/mol). Subtract the sum of these masses from the original mass of the compound to find the mass of oxygen.
Determine the moles of oxygen in the compound by using the mass of oxygen calculated in the previous step and the atomic mass of oxygen (16.00 g/mol).
Find the empirical formula by dividing the moles of each element by the smallest number of moles calculated. Then, determine the molecular formula by comparing the empirical formula mass to the given formula mass (120 g/mol) and adjusting the subscripts accordingly.
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