Separation Techniques

from the one and only Ethan Widjaja

Physical means of separation

• Filtration (gravity separation) -
  • Used to separate heterogeneous mixtures composed of solids and liquids.
  • Sues a porous barrier to separate the solid from the liquid.
  • Smaller particles of liquid passes through leaving the solid in the filter paper.
  • Prefer not to use it for gasses, only looking at filtration by gravity separation.
• Chromatography
• Centrifuging - separate plasma from blood.
• Evaporating - used to separate a solute from the solvent in a solution.
  • add heat to salt and solution, evaporate the solvent completely.
  • Evaporisation is a process of vaporisation
• Crystallization -
  • Separation technique results in formation of pure solid particles from a solution containing the dissolved substance
  • As one substance evaporates, the dissolved substance comes out of the solution and collects as crystals.
  • Produces highly pure solids
  • Example: rock candy.
  • if compound is not thermally stable, will produce pure crystals.
• Dissolving -
• Decantation -
  • Separate particulates from a liquid by allowing solids to settle to the bottom of the mixture while pouring off the particle-free part of the liquid.
  • Another methods is to allow two miscible liquids to separate, and the lighter liquid is poured off.
• Sieving -
  • A porous material used to separate particles of different sizes.
  • Most commonly used to affect gross separations, as of liquids from suspended crystals or other solids.
  • To accelerate filtration, pressure usually is applied (vacuum filtration)
    • Use for smaller particles of solids (normally organic compounds)
  • A series of sieves is tacked, those with the screen of largest holes size at the top.
• Flotation
• Distillation -
  • Used to separate homogeneous mixtures
  • Based on differences in boiling points of substances involved.
• Solutions
  • A mixture in which the solute particles are homogeneously distributed throughout particles of solvent.
    • Can be solid.
  • Aqueous solution: liquid solution where the solvent is water
  • Solvent: the major component of a solution by mass
  • Solute: the minor component of a solution by mass
  • Dissolving: solid particles are separated and distributed throughout the mixture, increasing solution concentration.
  • note that a solution can be also a solid and gas.
    • Solution with water is aqueous.
• Unsaturated: contains less solute than the solvent is normally able to dissolve
• Saturated: contains the same amount of solute that the solvent is normally able to dissolve
  • Rate of dissolving and crystallisation are equal.
• Supersaturated: contains more solute than the solvent is normally able to dissolve

  • Can be achieved through heating and dissolving, then carefully cooling the solution.

Lucarelli's brief description for separation

Pure substance: An element or compound, i.e. it has a fixed composition, cannot be separated into other substances unless through chemical means (compounds). - has a constant melting/boiling point

Density of a pure substance is fixed, so it hardness, electrical conductivity, colour

Mixture separation using physical properties:

Why? Mixtures do not have well-defined, set properties such as melting points, so understanding the nature of matter would be difficult using mixtures.

Main properties - pure substances in a mixture:

• Solubility
• Density
• Boiling point
• Particle size

Separation Techniques:

• Sieving: Separates components of a mixture based on particle size.

• Filtration and evaporation: Separates components based on solubility and volatility.

  • Filtration is a form of sieving.

• Gravity separation: Separates based on densities

  • Decanting: Separates solid-liquid mixtures based on densities.

• Distillation: Separates based on boiling point differences.

• Fractional distillation: Separates components with really close boiling points.

my bad notes

Separation techniques:

Diagram Notes: 2d and with ruler - Note: (D) means you need to be able to draw a diagram of this separation technique.

Sieving:

• A porous (containing pores) material is utilized to separate particles of different sizes.
• Physical Property: Particle size
  • Note: sieves can be stacked upon each other, with the largest pores at the top, to separate mixtures with more than 2 different particle sizes.

Filtration: (D)

• A porous material separates a solid from a liquid in a mixture.
  • Physical property: Particle size
  • The solid should not be soluble in the liquid.

Decanting:

• Separates particulates (solids in water?) from a liquid, by letting the solids settle at the bottom of the mixture while pouring off the particle free liquids.

  • Physical property: Density

• This also works with immiscible liquids, with the lighter one being poured off.

  • This is where the separating funnel comes in (D):
    • Separates multiple liquids by partitioning the constituents based on their density.

  

Distillation (D):

• Separates homogenous mixtures (solutions), based on the boiling points of its constituents. In general, aqueous constituents are converted into a gaseous state, and reconverted back into a liquid (as distillate).
  • Remember to label the blocky thing condenser!!
• Can be used to separate more than 2 liquids, if they have different boiling points
• This is called a 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.

  

Crystallisation:

• Creates a pure solid structure composed of a formerly dissolved constituent. - only works for homogenous mixtures (solutions)

  • When the solvent evaporates, the dissolved constituent collects as crystals.
  • Essentially, the solubility of a solution is rapidly increased and decreased(using heat generally)

  

Vaporisation:

• Extracting dissolved solute from a solution. Essentially, use this over distillation if you don’t care about the liquid.
• Heat is used to evaporate the liquid, leaving only the dissolved solute.
  • NOTE: DO NOT use vaporisation if your substance is extremely volatile or decomposes at high temperature, such as Ammonium Nitrate.

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

(NOTE TO SELF: research titration)

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