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Kinetic Theory

The Avogadro constant, the mole and molar mass

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Overview

Avogadro constant and physical meaning of the Boltzmann constant.

What you need to know

Answer each one before you reveal it.

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Numbers

Nitrogen has a relative molecular mass of 28.0. Calculate the number of molecules in 0.0140 kg of nitrogen.

Key term

Define the Avogadro constant.

Key term

State the value and unit of the Avogadro constant.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define the Avogadro constant.

    Model answer

    The Avogadro constant is the number of particles in one mole of a substance.

  2. 2

    State the value and unit of the Avogadro constant.

    Model answer

    The Avogadro constant is 6.02 × 10²³ mol⁻¹.

  3. 3

    Define the mole in terms of the Avogadro constant.

    Model answer

    A mole is the amount of substance that contains a number of particles equal to the Avogadro constant.

  4. 4

    State the relationship between the molar mass in kilograms and the relative molecular mass.

    Model answer

    The molar mass in kilograms is the relative molecular mass divided by 1000, so M = Mᵣ/1000 kg mol⁻¹.

  5. 5

    State how the number of moles in a sample is calculated from its mass.

    Model answer

    The number of moles is the total mass of the sample divided by the molar mass of the substance.

  6. 6

    Oxygen has a relative molecular mass of 32.0. State its molar mass in kg mol⁻¹.

    Model answer

    The molar mass is 32.0 ÷ 1000 = 0.0320 kg mol⁻¹.

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