Complete combustion of a 0.40-mol sample of a hydrocarbon, CxHy, gives 2.40 mol of CO2 and 1.60 mol of H2O. The molecular formula of the original hydrocarbon is
Group of answer choices
C2H8.
C6H8.
C9H16.
C5H5.
C4H7.
ؤ2ا2
To determine the molecular formula of the original hydrocarbon, we need to find the empirical formula first.
Step 1: Calculate the moles of carbon and hydrogen in the products.
From the balanced equation for the combustion of hydrocarbons, we know that 1 mol of hydrocarbon will produce the same number of moles of carbon dioxide (CO2) and water (H2O).
Given:
Moles of CO2 = 2.40 mol
Moles of H2O = 1.60 mol
Therefore, the number of moles of carbon in the original hydrocarbon = 2.40 mol
And the number of moles of hydrogen in the original hydrocarbon = 1.60 mol
Step 2: Determine the empirical formula using the moles of carbon and hydrogen.
Since the ratio of moles of carbon to moles of hydrogen helps us determine the empirical formula, let's divide the number of moles of carbon and hydrogen by their greatest common divisor (GCD).
GCD(2.40, 1.60) = 0.80
Dividing by 0.80:
Moles of carbon = 2.40 mol / 0.80 = 3.00 mol
Moles of hydrogen = 1.60 mol / 0.80 = 2.00 mol
Therefore, the empirical formula of the hydrocarbon is C3H2.
Step 3: Determine the molecular formula using the molecular weight information.
To find the molecular formula from the empirical formula, we need to know the molecular weight of the hydrocarbon.
Without the molecular weight information, it is not possible to determine the specific molecular formula of the hydrocarbon. Therefore, none of the answer choices provided can be determined as the correct molecular formula.
To find the molecular formula of the original hydrocarbon (CxHy), you can use the given information about the moles of carbon dioxide (CO2) and water (H2O) produced during the combustion.
First, let's calculate the number of moles of carbon (C) and hydrogen (H) present in the given compounds:
1 mol of CO2 contains 1 mol of C.
Therefore, 2.40 mol of CO2 contains 2.40 mol of C.
1 mol of H2O contains 2 mol of H.
Therefore, 1.60 mol of H2O contains 2 * 1.60 = 3.20 mol of H.
Now, we need to find the ratio of carbon to hydrogen in the original hydrocarbon. We can do this by dividing the number of moles of carbon by the number of moles of hydrogen:
Ratio = Moles of Carbon/Moles of Hydrogen
Ratio = 2.40 mol C / 3.20 mol H
Ratio = 0.75
Since the ratio of carbon to hydrogen is 0.75, we need to find a hydrocarbon where the ratio of carbon to hydrogen is approximately 0.75. Let's analyze the answer choices:
- C2H8: Ratio = 2/8 = 0.25 (Not a match)
- C6H8: Ratio = 6/8 = 0.75 (Close, but let's check other options)
- C9H16: Ratio = 9/16 ≈ 0.56 (Not a match)
- C5H5: Ratio = 5/5 = 1.0 (Not a match)
- C4H7: Ratio = 4/7 ≈ 0.57 (Not a match)
Therefore, the molecular formula of the original hydrocarbon is C6H8.
the product has 2.4 moles of C and 3.2 moles of H
... this from a 0.40 moles sample that was combusted
look at the mole ratios of the possible answers