Take a look at the following example👀
Describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallization and paper chromatography.
Simple Distillation
This method is usually used to separate the liquid from a solution of dissolved salts.
Process: During distillation, seawater is heated until the boiling point is reached and begins to vaporize. Then, the steam passes through the inner tube of the condenser where it will be cooled down by the cold water flowing around the condenser. Finally, the steam condenses to pure water (distillate) which is collected in the conical flask.
👁🗨Key Points
- Anti-bumping granules are added to ensure even boiling
- For the condenser, water in is at the bottom while water out is at the top
- The thermometer should be right next to the mouth of the condenser
Fractional Distillation
This is usually used to separate a mixture of two miscible liquids.
Process: Different substances have different boiling points. Therefore, when the mixture is heated and it evaporates, it will condense at different temperatures. As the mixture travels up the tube the temperature decreases, substances begin to condense at different places thus allowing the mixture to be separated into different parts.
Filtration
Thi method is used to separate an insoluble solid from a liquid.
Process: When a mixture is poured into a filter funnel with a filter paper, insoluble solids such as mud (residue) remain on the filter paper. Whereas, water (filtrate) can pass through the filter paper.
👁🗨Key Points
- A piece of filter paper has millions of tiny holes which allows water to pass through it while insoluble solids get caught by it
Crystallization
This method is used to separate a dissolved solid from a solution. There are two different techniques.
I- Cooling a Hot Concentrated Solution
Process: Heat the solution to removes some solvent. As the solvent boils, the solution will become concentrated. When the hot concentrated solution cools down, the solvent cannot hold all the solutes. Hence, the extra solutes will separate as crystals.
❗️❕A hot solvent can dissolve more solute than a cold one
II- Slow evaporation of a Solution
Process: When the solution evaporates, it becomes more and more concentrated. The solution will finally become saturated and when it is further evaporated, extra solutes will separate out as crystals.
👁🗨Key Points
- The crystals can be separated from the solution by filtration
Paper Chromatography
This method is used to separate the parts of a mixture into their components
Process: Spot of a solution is applied on a base-line on the paper. Once the spot is dried, the paper will be placed in a developing solvent. Then, the solvent rises up the paper while taking the components of the solution with it. Compounds that are more soluble in the developing agent will travel up more quickly thus separating the components.
❗️❕Each component will move up the paper at different rates depending on how strongly they stick to the paper and how soluble they are in the solvent
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