Ideal and Real Solutions: Raoult, Henry and Excess Functions · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When solutions stop being ideal

Science · Chemistry · ages 20-22
Name ______________________   Date ____________

  1. Measured vapour pressures sit above the ideal line. What is this?

    • Negative deviation
    • Ideal behaviour
    • Positive deviation

  2. A solution holds a large amount of solvent and a trace of solute. Which law fits each?

    • Raoult for both partners
    • Raoult for the solvent, Henry for the dilute solute
    • Henry for the solvent, Raoult for the dilute solute

  3. An azeotrope cannot be separated by simple distillation.

    Circle one:   True   False

  4. A pair of liquids shows positive deviation and takes in heat when mixed. What does that suggest about the contacts?

    • Unlike contacts are weaker than like ones
    • Unlike contacts are stronger than like ones
    • Contacts have no link to the deviation

  5. A mixture shows negative deviation. What does that say about the contacts?

    • Unlike contacts are stronger and hold molecules in
    • Unlike contacts are weaker and push molecules out
    • Contacts play no role in deviation

  6. Why does a fizzy drink hiss when you open it?

    • Henry's law links dissolved gas to partial pressure, which suddenly falls
    • Raoult's law forces all gas out of every liquid
    • Opening the bottle heats the drink sharply

  7. A student boils an azeotropic mix and collects the vapour, expecting pure ethanol. What happens?

    • Pure ethanol arrives, since boiling always purifies
    • The same mix arrives, since vapour matches liquid
    • Pure water arrives, since water boils first

  8. A mixture shows negative deviation. What sign does its excess Gibbs energy carry?

    • Positive, matching positive deviation pairs
    • Negative, like the deviation
    • Zero, since excess functions ignore deviation
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Answer key

For grown-ups. Fold this page away before handing over the rest.

When solutions stop being ideal W1-mt_DRHoU0yg3Z-s1

  1. Positive deviation · Above the line means molecules escape more easily than ideal.
  2. Raoult for the solvent, Henry for the dilute solute · Each law fits one end of the composition range.
  3. True · Boiling an azeotrope changes nothing, since vapour matches liquid.
  4. Unlike contacts are weaker than like ones · A raised vapour pressure and heat taken in both point to weaker unlike contacts: molecules escape the mixture more easily than their pure liquids.
  5. Unlike contacts are stronger and hold molecules in · Stronger unlike grips lower the escaping tendency.
  6. Henry's law links dissolved gas to partial pressure, which suddenly falls · Less pressure above means less gas can stay dissolved.
  7. The same mix arrives, since vapour matches liquid · Shared composition means boiling cannot shift the mix.
  8. Negative, like the deviation · The excess sign follows the deviation sign.
Worksheet · LightMySky