Below is the question and right after is my work.
Problem:
Excess fluorine (F2) reacts at 150 degrees C with bromine (Br2) to a compound BrFn (n = variable # i.e. n = 2 = F2). If 423 mL Br2 at 150 degrees C and 748 mmHg produced 4.20 g BrFn, what is n?
My work:
PV = nRT
n=PV/RT
n = [(.9842 atm)(.423L)]/[(.0821)(423.15)
n = .011983698 moles Br 2
Out of the 4.20 grams of BrFn 1.91499494 grams is Br2
I don't know what to do after here. What's my next step?
Thank you
I would suggest you divide the 1.915 g Br2 by 2 to determine the number of grams of Br (not Br2), then subtract from 4.20 g BrFn to determine the grams F.
Then (g F/atomic mass F) = moles F
and (g Br/atomic mass Br) = moles Br.
Finally, determine the ratio of the moles of one to moles of the other. The easiest way to do that is to take the smaller number and divide it by itself (thereby making 1.00 for that element), then divide the other number by the same small number. You should end up with a set of small whole numbers, or at least one that can be rounded to a whole number.
To determine the value of "n" in the compound BrFn, you need to use the stoichiometry of the reaction and the molar masses of the substances involved.
1. Determine the molar mass of bromine (Br2):
The molar mass of Br2 is the sum of the atomic masses of two bromine atoms, which is 79.9 g/mol.
2. Calculate the moles of Br2 used in the reaction:
You already have the mass of Br2, which is 1.91499494 grams. To convert this to moles, divide by the molar mass:
moles of Br2 = 1.91499494 g / 79.9 g/mol = 0.023964 moles of Br2
3. Use the stoichiometry to find the moles of BrFn:
The coefficient of Br2 in the reaction is 1, and the coefficient of F2 is n. Therefore, since you know that 0.023964 moles of Br2 react with the excess F2 to produce 4.20 grams of BrFn, you can set up a proportion to solve for n:
0.023964 moles Br2 / 4.20 grams BrFn = 1 mole Br2 / n moles F2
Cross-multiply and solve for n:
n = (4.20 grams BrFn * 0.023964 moles Br2) / (1 mole Br2)
n = 0.10067536 moles F2 (rounded to four decimal places)
Therefore, the value of n in BrFn is approximately 0.1007.
you know how many moles of Br2, so you know how many moles of Br (.02396)
Now you have 4.20gramsBr, of that, 4.20-1.915g is Fluorine., or .1204 moles
ratio of Fl/Br= .1204/.02396=5