Final answer:
To find the number of bromine atoms in 25.0 grams of liquid bromine, calculate the moles using the molar mass of bromine (Br₂) and then multiply by Avogadro's number and 2, yielding approximately 1.88 x 10²³ atoms.
Step-by-step explanation:
To determine how many atoms of bromine are in 25.0 grams of liquid bromine, we first need to calculate the number of moles of bromine in that mass. Based on the information provided, the average atomic mass of bromine is calculated using the isotopic masses and abundances of its isotopes, 79Br and 81Br. The average atomic mass of bromine (Br₂) can be calculated as follows:
Average atomic mass = (78.9183 amu × 50.69%) + (80.9163 amu × 49.31%) = 39.94 amu + 39.90 amu = 79.84 amu for Br, but since bromine exists as a diatomic molecule Br₂, the molar mass would be approximately 159.68 g/mol.
Now, using the molar mass, we can convert the mass of bromine to moles:
Moles of Br2 = 25.0 g ÷ 159.68 g/mol ≈ 0.1565 mol
Since each molecule of bromine (Br₂) contains 2 atoms of bromine, the total number of bromine atoms is:
Atoms of Br = 0.1565 mol × (6.022 × 10²³ atoms/mol) × 2 = 1.88 × 10²³ atoms