TOPIC 2: States of Matter and separation techniques/mixtures

Question 1

Explain the change in terms of particles from a solid –> liquid and a liquid –> gas

Answer 1

When heated, the solid gains kinetic energy and the tightly packed, uniform particles begin to vibrate more rapidly which weakens the forces holding the solid together
Then, as the melting point is reached, the particles have enough energy to break some of the bonds between particles and become a liquid. In this state, the particles are free to move over each other.
As temperature further increases, enough energy is gained to make the particles move faster to overcome the remaining intermolecular forces forming a gas.

Question 2

What is Purity?

Answer 2

When a substance only contains single element or compound

Question 3

How can you test for Purity?

Answer 3

When heated, pure substances have a specific melting and boiling point.
Mixtures melt gradually over a range of temperatures.

Question 4

What is the difference between fractional distillation and simple distillation?

Answer 4

You can only use simple distillation to separate things with very different boiling points. Fractional distillation can be used to separate a mixture of liquids with similar boiling points.

Question 5

Explain Crystallisation

Answer 5

Used to separate a soluble solid from a solution.
- Heat solution in evaporating basin gently
- Some of the water will evaporate so the solution will get more concentrated
- When the crystals begin to form, leave the solution to cool
- Filter the crystals out of the solution, leave them in a warm place to dry

Question 6

In paper chromatography, how does the solubility relate to its movement in the mobile phase?

Answer 6

Molecules with a higher solubility in the solvent (less attracted to the paper) will spend more time in the mobile phase than stationary phase - so they’ll be carried further up the paper

Question 7

What are the mobile and stationary phases in paper chromatography?

Answer 7

Mobile - The solvent (water/ethanol)
Stationary - The filter paper

Question 8

What’s the formula for finding ‘Rf’ values?

Answer 8

Distance travelled by solute / Distance travelled by solvent

Question 9

How can you use chromatography to see if a substance is pure?

Answer 9

If the blob moves as one, it is pure

Question 10

Explain the water purification process.

Answer 10

1) Filtration - Wire mesh screens out large twigs etc.. gravel and sand beds filter out other solid pieces
2) Sedimentation - Iron sulphate or aluminium sulphate is added to the water, making the fine particles clump together and settle at the bottom
3) Chlorination - Chlorine gas is bubbled through wate to kill harmful bacteria and other microbes

Question 11

What are the Pros and Cons of distilling sea water?

Answer 11

• In very dry countries, sea water is distilled to produce drinking water
• Distillation requires a lot of energy, so it is expensive
• So, we don’t tend to use this in the UK