A sample of a compound containing only Br and O reacts with an excess of H2 to give 6.601 g of HBr and 3.919 g of H2O. What is the empirical formula of this compound?
a. BrO
b. BrO2
c. Br2O
d. BrO3
e. None of the above
I already know the answer is (e), but I am not entirely sure how this answer is reached. Please correct me if I am wrong in any of my calculations:
____ + H2 --> HBr + H2O
(the space is the unknown compound)
6.601 g * (1 mol/80.9119 g) * (1 mol Br/1 mol HBr) = .0815 mol Br
3.919 g * (1 mol/18.0148 g) * (1 mol O/1 mol H2O) = .2175 mol O
This was as far as I got while it still made sense; as I continued I got some outrageous answer like Br19O50. Any help on figuring this out is greatly appreciated!
I have the following although I don't think I've ever seen this compound and I don't know what it is.
BrxOy + H2 ==> HBr + H2O
mols HBr = 0.08159
mols H2O = 0.2177
There is 1 mol Br in 1 mol HBr so we mut have started with 0.08159 mol Br in BrxOy.
I see only 1 mol O in H2O; therefore, we must have started with 0.2177 mol O in BrxOy.
Therefore I wrote the formula of BrxOy as
Br(0.08159)O(02177)
mols Br = 0.08159
mols O = 0.2177
Divide by the smaller number to get a ratio with 1.00 being the smallest number.
Br = 0.08160/0.08159 = 1.00
O = 0.2177/0.08159 = 2.668
2.668 is too far from 2.0, 2.5 or 3.0 to round; therefore we try find multiples of 1.00 and 2.668.
1.00 x 2 = 2.00
2.668 x 2 = 5.34. Still not whole numbers.
1.00 x 3 = 3.00
2.668 x 3 = 8.004 and we can round this to 3:8
I would write the formula as Br3O8.
Thank you so much, this makes much more sense than what I was doing; I was dividing each amount by the number of moles of O, not Br, which explains why I was getting crazy numbers.
To determine the empirical formula of the compound, we need to find the simplest whole number ratio of atoms in the compound.
Given:
Mass of HBr produced = 6.601 g
Mass of H2O produced = 3.919 g
Step 1: Calculate the number of moles of HBr and H2O produced.
Molar mass of HBr = 1.00784 g/mol (H) + 79.904 g/mol (Br) = 80.9119 g/mol
Molar mass of H2O = 1.00784 g/mol (H) + 15.999 g/mol (O) = 18.0148 g/mol
Number of moles of HBr = mass of HBr / molar mass of HBr
= 6.601 g / 80.9119 g/mol
= 0.0815 mol
Number of moles of H2O = mass of H2O / molar mass of H2O
= 3.919 g / 18.0148 g/mol
= 0.2175 mol
Step 2: Determine the smallest whole-number ratio of the elements.
Divide the number of moles of each element by the smallest number of moles obtained.
Smallest number of moles = 0.0815 mol (HBr)
Number of Br atoms = 0.0815 mol (Br)
Number of O atoms = (0.2175 mol (H2O)) / 2 (because there are 2 H atoms per water molecule)
Number of Br atoms = 0.0815 mol
Number of O atoms = 0.1088 mol
Let's find the ratio of Br to O by dividing by the smallest number of moles:
Br:O = (0.0815 mol / 0.0815 mol) : (0.1088 mol / 0.0815 mol)
= 1 : 1.333
Since we need a whole number ratio, we can multiply both numbers by 3 to get a ratio of 3 : 4.
Br:O = (1 x 3) : (1.333 x 3)
= 3 : 4
Therefore, the empirical formula of the compound is Br3O4. None of the given options (a, b, c, or d) match the empirical formula, so the correct answer is (e) None of the above.