A gaseous hydrocarbon (an organic compound consisting of C & H) weighing 0.232g occupies a volume of 102mL at 23 degrees Celcius and 749mmHg.
Calculate the molar mass and identify the compound. The compound is:
a)C2H4
b)C3H6
c)C4H8
d)C5H10
e)C6H12
How is this problem worked out to get "c"...C4H8??? Do I use PV=nRT?...if so...how is it used for this problem?
PV=nRT
P = (749/760) atm.
V 0.102 L
solve for n. I get 0.004139
R = 0.08205 L*atm/mol*K
T = 273 + 23
# mols = g/molar mass.
you have mols and you have g. Solve for molar mass.
I get 56.
If it is a hydrocarbon, then 1C and 2H units is 14. 56/14 = 4 units of CH2
(CH2)4 = C4H8 OR you can just go down the list and calculate the molar mass of each of the answers.
a is 28, b is 42, 3 is 56, d is 70 and d is 84. Easy to pick out.
great! thank you!
so basically all that I had to do was 13/0.232? PV=nRT really had nothing to do with the problem then?
You used the ideal gas law PV=nRT to solve for the number of moles.
Mass= number of moles * molar mass
then you solved this for molar mass.
Yes, you are correct. In this problem, you used the ideal gas law, PV=nRT, to solve for the number of moles of the gaseous hydrocarbon. However, you didn't need to use the ideal gas law to calculate the molar mass.
The given mass (0.232g) and the calculated number of moles (0.004139) allowed you to determine the molar mass by dividing the mass by the number of moles.
After calculating the molar mass, you correctly identified the compound as C4H8 by comparing the calculated molar mass to the molar masses of the given options (C2H4, C3H6, C4H8, C5H10, C6H12).
So, to summarize:
- You used PV=nRT to calculate the number of moles.
- You used the number of moles and the given mass to calculate the molar mass.
- You compared the calculated molar mass to the molar masses of the given options to identify the compound.