A 1.082 g sample of a component of the light petroleum distillate called naptha is found to yield 3.317 g CO2 and 1.584 g H2O on complete combustion
This particular compound is also found to be an alkane with one methyl group attached to a longer carbon chain and to have a molecular formula twice its empirical formula
The compound also has the following properties:
melting point: -154 C
boiling point: 60.3 C
density: 0.6532 g/mL at 20.0 C
specific heat: 2.25 J
DeltaH f = -204.6 kJ/mol
Use the masses of CO2 and H2O to determine the empirical formula of the alkane component.
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First i calculated the number of moles of Carbon and Hydrogen present in the unknown:
Carbon:
Molar mass = 43.99
CO2 mass - 3.317 g
moles= 0.0754
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Hydrogen:
Molar mass: 18.01
Mass of H20- 1.584 g
moles = 0.08795
Since there are 2 hydrogens in H2O
the moles are 0.01760.
And then i divide the moles by the lowest number:
Carbon: 0.0754/ 0.0754 = 1
Hydrogen: 0.0879/ 0.0754 = 1.16
I am not sure what to do next...
You're on the right track but you didn't start quite right. You haven't taken into account the mass of the sample. I would have determined the %C and %H, then converted those to mols and found the ratio from that.
i figured that the answer was C3H7
I found the mass percentage of C and H. Then I calculated the mass of C and H with the percentage.
Then I used the calculated masses to determine the number of moles of C and H. With that, I divided out the moles with the smallest number of moles. You should have gotten 1:2.33333333. In which you multiply by 3, to get the answer
Next, you need to find the ratio of the moles of carbon to hydrogen in the alkane compound. Since the empirical formula is the simplest ratio of atoms in a compound, you want to convert the ratio of moles to a whole number ratio.
To do this, you can divide both the moles of carbon and hydrogen by the smaller value (in this case, 0.0754 moles of carbon).
Carbon: 0.0754 moles of carbon / 0.0754 moles of carbon = 1
Hydrogen: 0.0879 moles of hydrogen / 0.0754 moles of carbon = 1.165
Now, you need to convert the ratio to whole numbers by multiplying both values by a whole number to get the nearest whole number value.
In this case, multiplying both values by 2 gives a ratio of 2:2.33, which can be rounded to 2:2.
So, the empirical formula of the alkane compound is CH2.
Now, let's determine the molecular formula of the alkane compound.
Given that the molecular formula is twice the empirical formula, the molecular formula of the alkane compound is C2H4.
Therefore, the empirical formula of the alkane component is CH2 and the molecular formula is C2H4.