R-AECHE-4

Objectives:

5 (Essential skills). Write and use balanced chemical equations to represent chemical reactions

1. Explain the relationship between the identity and relative amounts of substances om a solution, and its properties.
2. Explain how differences in physical properties of substances in a mixture can be used to separate them.
3. Describe a range of separating techniques, and explain which physical property is utilised in the method of separation.

Diagram Notes: 2d and with ruler

• Filtration - filtration uses both solubility of a substance + particle size (D)
  • For a solid and a liquid (insoluble substance)
  • Uses a filter to allow the liquid to pass through (usually using small pores) but prevents the solid from passing.
  • The solid should not be soluble in the liquid.

Methodology:

1. Place filtered paper in a funnel. Place this funnel above a flask.
2. Pour the mixture into the funnel.

• Use of separating funnel (D)

  • Uses differences in density
  • Involves 2 liquid that form a heterogenous mixture.

• Distillation - based on different boiling points (D)

  • Water - 100 degrees celcius
  • Ethanol - 76-78 degrees celcius
  • label condenser
  • Distillation refers to the process of converting a liquid into a gaseous state, and then back into a liquid.
  • Used to separate 2 or more liquids with different boiling points.
  • Vapour is collected and condensed using a condenser.

• Distillation apparatus

• Fractional distillation (D) - not overly complex diagram e.g. for crude oil

  • Used when separating mixtures with similar boiling points
  • In general, the path that the boiled products take to reach the condenser is extended, or surface area is increased, usually through the use of glass beads
  • In theory (Kinetic theory of gas particles), the lower-boiling liquid will have a lot of kinetic energy, whereas the higher-boiling liquid will have less as it approaches its boiling point but does not completely reach or exceed it. The increase in surface area makes it more likely for the higher-boiling liquid to lose its energy and fall back down as a liquid.
  • This increases the purity of the condensed product.
  • E.g. if you have 2 liquids with boiling points 65 and 75, and you place it in a fractional distillation apparatus that boils at a temperature of 70, the 65-liquid would be in a temperature that exceeds their boiling points, so they would have a lot of energy (higher temperatures causes gasses to move faster), so they are much more likely to be able to reach the top due to their high kinetic energy. The 75-liquid would not be as highly charged, however a small portion of its particles may become gaseous. However, the increase in surface area creates a large chance that these particles will hit into the surface area, and as they don’t have much energy they will fall back down as a liquid.

• Crystallization

• Electrostatic attraction

  • Repulsion/attraction due to charged particles

• Magnetic susceptibility

  • Metals reacting with a magnetic field (magnet)

• Vaporisation

  • If the substance you are looking for decomposes at high temperatures, dont use
  • e.g. Ammonium Nitrate

• Decanting

• Sieving

(D) = need to know how to draw diagram

Separating Mixtures:

• Mixtures can be separated by any means that makes use of the different physical properties of its constituents.
• The properties of the components of a mixture determine the best separation method

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