Final answer:
The molar mass of bromine is calculated by taking the weighted average of its isotopes' masses and abundances. For bromine, this results in an atomic mass of approximately 79.90 amu. The molar mass for Br2 is then 159.80 g/mol, leading to the molecular formula Br2 and closely matching option A).
Step-by-step explanation:
To determine the molar mass of bromine and its molecular formula, we need to calculate the average atomic mass of bromine based on the two major isotopes, 79Br and 81Br, and their abundances. The average atomic mass is the weighted sum of the isotopic masses and their respective abundances.
The calculations for the average atomic mass of an isotope of bromine are:
- 79Br: 78.9183 amu * 0.5069 = 40.00 amu
- 81Br: 80.9163 amu * 0.4931 = 39.90 amu
Adding these weighted masses together gives the average atomic mass of a bromine atom:
40.00 amu + 39.90 amu = 79.90 amu
To obtain the molar mass for bromine gas (Br2), we multiply the atomic mass by 2, as there are two atoms of bromine in each molecule:
Molar mass of Br2 = 79.90 amu * 2 = 159.80 g/mol
The molecular formula of bromine is Br2 and its molar mass is approximately 159.80 g/mol, which corresponds to option A).