A student obtains a sample of liquid bromine at 20 degrees Celsius. She measures the volume to be 25.0cm³ and she looks up the density of bromine which is 3.1 g/cm³. How many moles are in the sample.

0.485 moles of Br₂ are in the sample

Explanation:

Density is a physic constant.  It is specific to each substance or compound and as an intensive property, it varies with temperature

Density = Mass / Volume

Density of Br₂ = Mass of Br₂ / Volume of Br₂

Therefore, Mass of Br₂ = Density of Br₂ . Volume of Br₂

Mass of Br₂ = 3.1 g/cm³ . 25cm³ = 77.5 g

Let's convert the mass to moles → 77.5 g / 159.8 g/mol = 0.485 moles

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