separations

• A pure substance is made out of one single element of a compound. Example: water.
• A mixture is made up of two or more substances that are physically combined. Example: Air.
• To determine whether a substance is pure is by checking for an exact and fixed melting point of a liquid or by performing paper chromatography.
• Impurities lower the melting point. Impurities cause melting to take place over a range of temperatures. The greater the amount of impurities, the lower the melting point of the substance.
• Impurities increase the boiling point. Impurities cause boiling to take place over a range of temperatures. The greater the amount of impurities, the higher the boiling point of the substance.
• Filtration is used to separate insoluble solid from a solid-liquid mixture.
• A filter paper is used to separate the mixture because it has very tiny pores.
• The substance collected on the filter paper is called residue.
• The solution collected in the flask is called a filtrate.
• Only dissolved substances with particle size smaller than the pore size of the filter paper can pass through the pores. The insoluble solids are to large to pass through them.
• If a solid is heat-stable, evaporation can be used by heating the solution to dryness.
• If solution is non heat-stable, strong heat would decompose it.
• A saturated solution is a type of solution which no more solute can dissolve in it.
• If the cooling takes place quickly, the size of the crystals is smaller or powdery.
• Washing crystals with cold distilled water removes impurities.
• Placing the crystals in between the filter paper is to obtain dry crystals.
• Simple distillation is to separate a solid-liquid mixture.
• When the liquid is heated to reach its boiling point so that it changes into a vapour.
• The process involves two physical states. Boiling takes place in the distillation flask and condensation takes place in the condenser.
• The vapor cooled by the condenser and changed into a liquid that is collected is called a distillate.
• The bulb of the thermometer must be placed near the mouth of the condenser to measure the boiling point of the substance accurately.
• during a boiling of a substance, the temperature remains constant.
• A conical flask is used instead of a beaker because of its narrow neck which reduces the loss of distillate from splashing out.
• If the distillate is volatile, it can evaporate easily due to the heating effect from the heat source.
• The purpose of boiling chips is to ensure smooth boiling.
• Chromatography is used to separate a liquid-liquid mixture which is based on the solubility of different substances.
• The more soluble the substance in the solvent, the further the distance it travels on the paper.
• The spot on the chromatography paper shows the component in the same.
• The starting line in the chromatography paper marks the position of the dye.
• The solvent is to dissolve the sample substance.
• The solvent front on the chromatography paper is to mark the end position of the solvent travelling on the paper.
• The lid prevents evaporation of the solvent.
• The solvent front should be as high as possible so it allows all the components to be fully separated.
• The starting line is drawn with a pencil because the pencil is insoluble to the solvent and will not interfere with the results.
• The sample must be applied as small as possible so that the smudging and tailing of different components will not occur.
• The number of spots indicates the number of substances in the sample.
• A single spot produced by a sample is a pure substance.
• Two or more spots produced by the sample is a mixture.
• The advantages for using chromatography gives a quick and accurate analysis of samples, it requires only a small amount of sample and it will be able to separate complex mixtures such as food dyes or flavouring.
• The applications of chromatography is used to detect small amount of banned substances in urine or blood samples.

  Monitoring the use of artificial flavouring and colouring in food industry

  Collecting the evidence of crimes such as identifying DNA fragments in forensic science.