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Starter for five

Starter for five. What is meant by the ‘density’ of a substance? What units are used when measuring the density of a substance? What state will a substance be in if it has a low density? Why?. Answers. The mass per volume e.g. the mass of 1cm 3 of the substance. gcm -3 or gl -1

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Starter for five

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  1. Starter for five • What is meant by the ‘density’ of a substance? • What units are used when measuring the density of a substance? • What state will a substance be in if it has a low density? Why?

  2. Answers • The mass per volume e.g. the mass of 1cm3 of the substance. • gcm-3 or gl-1 • a gas. The particles of a gas have lots of space between them so there will be only a small number of particles in the given volume compared to a solid or liquid whose particles have very little space between them.

  3. Higher ChemistryUnit 1(e) Gas densities and molar volumes

  4. After today’s lesson you should be able to: • state the equation showing the relationship between density, mass and volume of a gas. • state the equation showing the relationship between density, molar mass and molar volume of a gas. • calculate the density or molar volume of a gas given relevant information. • give the relationship between all gases at the same temperature and pressure

  5. Relationship between density, mass and volume • The units of density that are used to measure gases are gl-1. grams = massper l = volume i.e. density = massper volume = mass ÷ volume

  6. This relationship can be represented by the following triangle: mass (g) density volume (gl-1) (l)

  7. Relationship between density, mass and volume for one mole of a gas • This relationship can be expanded further to calculate the molar volume of a gas i.e. the volume taken up by 1 mole of a gas. molar mass (g) density molar volume (gl-1) (l)

  8. Example 1 The density of methane, CH4, is 1.06gl-1. Calculate the molar volume of this gas. From the triangle: Molar volume = molar mass ÷ density = 16 ÷ 1.06 = 15.1l

  9. Example 2 The molar volume of sulphur dioxide, SO2, is 26l. Calculate the density of this gas. From the triangle: density = molar mass ÷ molar volume = 64.1 ÷ 26 = 2.47gl-1

  10. Example 3 The density of a gas is 0.8gl-1 and its molar volume is 35l. Calculate the molar mass of this gas. From the triangle: Molar mass = density x molar volume = 0.8 x 35 = 28g

  11. Exercise Complete Q8.1 – 8.10 on p71 of ‘Test your Higher Chemistry Calculations’

  12. Relationship between all gases at the same temperature and pressure At 0oC and 1 atmosphere pressure, nitrogen gas, N2, has a density of 1.25gl-1. Its molar volume = molar mass ÷ density = 28 ÷ 1.25 = 22.4l

  13. Exercise • Using the table on p8 of your notes calculate the molar volume of oxygen, carbon monoxide and helium at the same temperature (0oC) and pressure (1atm). • What is the relationship between all gases at the same temperature and pressure?

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