There are 0.400 mol Br₂ in the sample..
Mass of Br₂ = 20.5 mL Br₂ × 3.12 g Br₂/1 mL Br₂ = 63.96 g Br₂.
Moles of Br₂ = 63.96 g Br₂ × (1 mol Br₂/159.81 mol Br₂) = 0.400 mol Br₂
The 20.5 ml of bromine sample has been consisted of 0.4 mol.
Density can be defined as the mass of an element per unit volume. The density (D) can be expressed as:
[tex]D=\dfrac{M}{V}[/tex]
Where, m has been the mass of the compound
V has been the volume of the compound.
The given Bromine has:
[tex]D=3.12\;\text {g/ml}\\V=20.5\;\rm ml[/tex]
The mass of bromine has been calculated by substituting the values as:
[tex]3.12=\dfrac{m}{20.5}\\\\m=3.12\;\times\;20.5\;\text g\\\\m=63.96\;\text g[/tex]
The mass of bromine sample has been 63.96 g. The moles of the sample has been calculated as:
[tex]M=\dfrac{m}{mwt}[/tex]
Where, mass of the substance, [tex]m=63.96\;\text g[/tex]
Molecular weight of the substance, [tex]mwt=159.81\;\text{g/mol}[/tex]
Substituting the values for calculating moles (M) as:
[tex]M=\dfrac{63.96}{159.81}\;\text{mol}\\\\M= 0.4\;\text{mol}[/tex]
The number of moles of [tex]\rm Br_2[/tex] present in 20.5 ml has been 0.4 mol.
For more information about density, refer to the link:
https://brainly.com/question/952755
