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SEPARATION TECHNIQUES - Coggle Diagram

- - - - Impurities lower the melting point of a substance
      - The greater the amount of impurities, the lower the melting point of the substance
      - Impurities cause melting to take place over a range of temperatures
    - - Impurities raise the boiling point of a substnace
      - The greater the amount of impurities, the higher the boiling point of the substance
      - Impurities cause boiling to take place over a range of temperatures
- - - - Magnetic attraction is used to separate magnetic substances from non-magnetic materials using a magnet
      - At the junk yard, electromagnets are used to lift, handle and load scrap steel and iron so that they can be recycled, by being re-mouldered into saleable material
      - In food processing magnetic separators are used to remove small amounts of iron containments such as ash content, unwanted magnetic stones so that the food is safe to be consumed
      - In hospitals magnets are used tor remove splinters from patient's eyes
    - - Sublimation is used to separate a solid that sublimes on heating from a solid that does not. A solid that sublimes undergoes a state change form solid gas without going through liquid state.
      - Physical properties of the components in the mixture: Iodine sublimes but not salt. So during heating, iodine turns into vapour while salt remains on the evaporating dish.
    - - This technique is sued to separate a mixture of two solids, in which one of the solids is soluble in a suitable solvent and the other solid is not.
      - Different solids dissolve in different solvents
      - Some common solvents are water and ethanol.
      - Physical properties of the components in the mixture: salt is soluble in water but not sand.
  - - - Filtration is used to separate an insoluble solid from a liquid in a suspension mixture.
      - In the lab, a piece of filter paper is placed in a filter funnel. The mixture is poured onto the filter paper.
      - The filter paper has very small pores. Only particles with a size smaller than the pores can pass through. The insoluble solids have larger particle size than the soluble liquid, hence are trapped on the filter paper, which allow the liquid to pass through.
      - The solid that remains on the filter paper is called the residue. The liquid that passes through is called the filtrate.
    - - Evaporation till dryness is used to separate a soluble dissolved solid from a solution. It is only used for substances that do not decompose on heating.
      - Evaporation till dryness an only be used for substances that do not decompose on heating, otherwise known as heat-stable substances.
      - The solid obtained by evaporation till dryness is not always pure. Any soluble impurities will be left together with the solid after the process is completed.
    - - Crystallisation is used to separate a soluble dissolved solid from a solution. It is used for substances that are not heat-stable.
      - The solution is heated to remove most of the solvent (water). Heating is stopped when a saturated solution is formed. The hot, saturated solution is allowed to cool. The dissolved copper (II) sulfate appears as pure crystals. The cold solution with crystals is filtered. The crystals are washed with a little amount of cold distilled water to remove impurities and filtered again. The filtrate contains soluble impurities. The crystals are then dried by pressing them between pieces of filter paper.
      - For Crystallisation to take place;
        
        Solid must be soluble in the solvent used
        
        Solubility of the solid should change with changing temperature
        
        Solvent used should be saturated with the solute.
      - A saturated solution is a solution that contains as much dissolved solute as it can at a given temperature.
      - Rapid cooling produces small crystals while slow cooling produces large crystals.
    - - Paper chromatography is used to separate or identify a small volume fo solutes dissolved in a solvent. It is done based on the different solubility of the components in a particular solvent.
      - A solution of the dye is obtained
      - A drop of the solution is placed on the pencil line near the bottom of a strip of filter paper.
      - The chromatographic paper is dipped into a solvent, e.g. water, with the solvent
      - The solvent moves up the paper
      - When the solvent reaches the spot of the dye, it dissolves the substances in the dye.
      - The difference substances move along with the solvent but at different rates.
      - The move soluble substances move faster and further up the paper than those that are less soluble in the solvent used.
      - The position of the solvent when the paper is removed is known as the solvent front.
      - The different substances move along with the solvent but at different rates.
      - The more soluble substances mov faster and further up the paper than those that are less soluble.
      - Thus, the substances in the mixture are seperated.
      - Locating agents is used int eh chromatography of colourless compounds. The locating agent reacts with the colourless substances to produce coloured products.
      - Identical dyes travel up the same distance and produce the same colour on the paper.
      - Rf value:
        
        The Rf value is the unique characteristic of the pure component and it can be used to identify the component present int the mixture.
        
        The ratio between the distance travelled by teh substance and the distance travelled by the solvent is a constant. This ratio is called the Rf value of the substance.
        
        The positions of the solvent front (position reached by solvent) and spot on a chromatogram depend on how long the experiment was allowed to run.
        
        What affects Rf value:
        
        Temperature of solvent: The solvent can better dissolve the chemicals at a higher temperature.
        
        Type of solvent: A solvent which has a stronger affinity for a particular chemical will easily overcome any affinity fo the chemical for the chromatography paper and move that chemical farther in a given period of time.
        
        Type of chromatography paper: Components of he mixture(s) will separate on the chromatography paper according to how strongly they absorb to it versus how much they dissolve into the solvent. The absorbance may be different for different types of chromatography paper.
        
        Different components in a mixture have solubility in a solvent
        
        The different solubility in a solvent causes them to move at different speeds on the chromatography paper
        
        Uses of chromatography:
        
        It is used to identify the contents of a mixture
        
        It is used to test the purity of a substance
        
        It is used to identify the contents of a mixture
        
        It is used to test the purity of a substance
        
        Advantages of paper chromatography:
        
        Only a small amount of samples is required
        
        It gives a fast and accurate analysis of a sample.
        
        It is able to separate complex mixtures such as food dyes
    - - Simple distillation is used to separate a liquid from a solution. The solution can be a solid-liquid mixture or a liquid-liquid (miscible) mixture
      - Simple distillation setup
        
        Thermometer bulb should be just beside the side arm leading to the condenser
        
        Boiling chips are marble/porcelain chips placed in the flask to ensure smooth boiling by reducing the bumping of liquid during boiling.
        
        Water enters the condenser from the bottom and leaves form the top. In other words, water flows in anti-current to the flow of the hot vapour. Condenser must be sloping downwards.
        
        Conical flask us used as the receiving flask because the narrow neck of the flask can reduce the loss of the distillate through splashing.
        
        Volatile liquids can be kept in the liquid state by placing conical flask in ice.
      - Simple distillation process
        
        Water boils and becomes vapour. Water vapour rises and enters the condenser.
        
        Thermometer measures boiling point of the vapour.
        
        Water vapour is cooled and condenses into pure liquid (distillate)
        
        The salt solution becomes more concentrated as distillation continues. Salt will be collected as residue.
        
        Pure water is collected as distillate
  - - - Fractional distillation is used to separate 3 or more miscible liquids. Generally, the liquids have boiling points that differ by less than 25 degree celcius from each other
      - Miscible liquids are liquids which dissolve in each other to form a single layer.
      - A fractionating column is attached to the round-bottomed flask and the condenser for fractional distillation.
      - Glass beads/plates/spiral int eh fractioning column provide a large surface area for vapour to condense on.
      - Fractional distillation setup:
        
        Ethanol vapour and water vapour rise up the column as the solution is heated.
        
        The water vapour condenses in teh fractionating column and falls back into the flask.
        
        Ethanol, which has a lower boiling point than water, reaches the upper part of the column and is distilled over.
        
        At this stage, the thermometer shows a constant temperature shows a constant temperature of 78 degree celcius, which is the boiling point of ethanol.
        
        In this condenser, hot ethanol vapour condenses as running water cools it; liquid ethanol flows down the inner tube of the condenser and into teh conical flask.
        
        Ethanol is collected as the distillate in the receiver.
        
        When all the ethanol has distilled over, the temperature rises rapidly to 100 degree celcius, which is the boiling point of water. At this temperature, water distills over and can be collected seperately.
      - Fractional distillation is able to separate different liquids in a mixture because they have have different boiling points.
      - A liquid with a lower boiling point will be distilled out first.
      - A fractionating column allows a liquid of higher boiling point to condense and fall back during the distillation of a substance of lower boiling point. This ensures separation of the liquids.
    - - The separating funnel is used to separate 2 or more immiscible liquids of different densities.