How much does 1 molecule of bromine weigh?
I know the atomic mass for bromine is 79.90 g but I do not know how to use it to figure out the weight of the molecule. The given answer is 2.654x10^-22 but I do not know how to get there.
First, the molecule of bromine is Br2. Since each atom of Br has a mass of 79.90, then two will be 79.90 x 2 = ??. That is the mass of 1 mol of Br2 molecules.
Next, there are 6.023 x 10^23 molecules in 1 mol of Br2. So if 6.023 x 10^23 molecules have a mass of 159.80, then how much mass is there is just 1 molecule?
Did you intend to ask for the mass of 1 atom of Br. If so, just divide the mass you find for one molecule of Br2 bt 2.
Thank you. Now I understand this one. There is one more problem that I need help with. A compound containing carbon, hydrogen, and oxygen atoms includes the following percent abundances: 79.4%C, 11.75%O, and 8.85%H. There are 2 oxygen atoms per molecule. How do you figure out the molar mass of the compound? The given answer is 272.3 g/mol. How can this be obtained?
Take a 100 g sample.
That will give you
79.4 g C.
11.75 g O.
8.85 g H.
Calculate the mols in each mass.
mols C = 79.5/12 = 6.625
mols O = 11.75/16 = 0.734
mols H = 8.85/1 = 8.85
So the empirical formula is
C6.625H<sub.8.85O0.734 but we know that these should be in the ratio of small whole numbers. We can make the smallest number 1 by dividing it by itself. To keep the proportion, we must divide all the other numbers by the same number. Therefore,
C = 6.625/0.734 = 9.02
O = 0.734/0.734 = 1.00
H = 8.85/0.734 = 12.1
Rounding these values to small whole numbers will give
C = 9; O = 1; H = 12 or the empirical formula is C9H12O.
The problem tells us that there are two O atoms per molecule; therefore, just multiply everything by 2. The molecular formula is C18H24O2. Calculate the molar mass from that. I hope this helps. Note that I didn't use exact values for C, H, and O atomic masses above. You should use exact masses to calculate the molar mass. Exact masses can be obtained from a periodic chart.
Thank you very much. Great explanation.