A gaseous compound has 36.4% carbon, 57.5% fluorine, and 6.1% hydrogen. A sample of 500mL of this gas has a mass of 1.48 grams. What is the molecular formula of this compound?
2006-10-14 16:37:44 · 4 answers · asked by redalert 2 in Science & Mathematics ➔ Chemistry
C F H
Percentage 36.4 57.5 6.1
Mass 36.4%*500 57.5%*500 6.1%*500
182 287.5 30.5
mol 182/12=15.2 287.5/19=15.1 30.5/1=30.5
ratio 15.1/15.1=1 15.1/15.1=1 30.5/15.1=2
1 : 1 : 2
Empirical formula = C1H2F1
Mass of Empirical Formula= 33g
Amount of empirical form in molec.= 148/33=4
Therefore= C4H8F4
NB - The mass given is too small. Is it correct!!!
2006-10-14 16:56:45 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Well, here is how it works:
Find out how many grams of carbon fluorine and hydrogen are in 1.48 gram of the compound. You have the percentage so you can find the net weight of each element:
1.48 x 36.4% = 0.58 gm of carbon
1.48 x 57.5% = 0.85 gm of fluorine
1.48 x 6.1 % = 0.1 gm of hydrogen.
Then Davide every quantity by the smallest quantity, o.1 gm:
0.58/0.1 = 5.8 for carbon
0.85/ 0.1 = 8.5 for fluorine
0.1/0.1 = 1 for hydrogen
Then round down. So your compound has 5 carbons, 8 fluroines and 1 hydrogen:
C5F8H
I think this is how you solve this kind of problems. It has been 2-3 years since my last chemistry course. Good Luck.
2006-10-14 23:52:49 · answer #2 · answered by smarties 6 · 0⤊ 1⤋
to find the empirical formula, let's just say that we have a 100g sample of the compound. So that means 36.4g of it is carbon, 57.5g is fluorine, and 6.1g is hydrogen. Convert those grams into the number of moles of each substance using the molar mass of each element. We need those moles in whole number ratios so, if necessary, you can multiply each of those moles by the same integer. Choose an integer that will make the 3 of them whole numbers. So now we've got an empirical formula. It's time to use PV=nRT. The only problem is that you havent specified if this is or isnt at STP. Assuming it is, plug in 1 for P, .500 for V, the gas constant for R, and 273 for T. Solve for n. Now you've got the number of moles and they've given you the grams for that number of moles. Find that molar mass ( grams/mole). Compare that molar mass to the mass of the empirical formula. You may need to multiply the subscripts of the empirical formula by an integer in order for the mass of it to add up to the molar mass you just calculated. Once you've done that, you've found the molecular formula
2006-10-14 23:46:41 · answer #3 · answered by Greg G 5 · 0⤊ 0⤋
Pay attention in class and do your own homework...
2006-10-14 23:45:34 · answer #4 · answered by sulfur_and_mercury 1 · 2⤊ 1⤋