Key Concepts in Chemistry - Separation and Purification

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to form. 3. Once all the water has evaporated, it leaves solid crystals behind. Simple Distillation: This is used to separate a solvent from a solution. It is useful for producing water from salt solution. Pure water vapour Salty water 78°C Fractionating column Pure ethanol vapour Water and ethanol solution 100°C 1. The Salty Water is being heated by the Bunsen Burner. 2. The Water Vapour Cools in the condenser and drips into a beaker. 3. The water has condensed and now in the beaker, the salt stays behind (solvent) Fractional Distillation: This is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water. T Heat Thermometer Cooling water in Cooling water out Vapour condenses in the condenser Electric heater Cooling water out Ethanol vapour condenses Cooling water in Water Ethanol Pure water 1. Water and Ethanol solution is heated. 2. The ethanol evaporates first, cools, then condenses into the beaker. 3. Change the beaker and then the water condenses after evaporation and cooling down. Paper Chromatography: This is used to separate mixtures of soluble substances. Often are coloured substances such as inks, food colourings and dyes Solvent Pencil line Interpretation of a Chromatogram: This practical is to distinguish between pure and impure substances: A pure substance produces one spot on the chromatogram An impure substance produces two or more spots Solvent front 1. The Ethanol and Water Solution is heated. 2. As the paper is lowered into the solvent, some of the dye spreads up the paper. 3. The paper has absorbed the solvent, and the dye has spread further up the paper. Chromatography relies on two different 'phases': ▸ Stationary Phase - the paper is very uniform, absorbent paper. Something that does not move e.g. The Chromatography Paper Mobile Phase - the solvent moves through the paper, carrying different substances with it Two substances can be the same if: Ink or plant dye They produce the same number of spots, and match the colour ➤ Have the same Rf Value - distance travelled by substance/ distance travelled by solvent Core Practical: Investigating the Composition of Inks. Aim: To investigate the composition of inks using simple distillation and chromatography. Simple Distillation Method: Results: 1. Add a small volume of ink to a flask. Connect the flask to the fractionating column and secure it with a stand, boss, and clamp. Results: 2. Attach a condenser to the top of the fractionating column, connect it to a cold water tap and sink, and secure it over a beaker. 3. Heat the flask using a Bunsen burner, reducing the flame as necessary to achieve gentle simmering. 4. Collect a small sample of the distilled solvent, then turn the Bunsen burner off. Describe the appearance of the distilled solvent, if your apparatus included a thermometer at the top of the column, record the maximum temperature reached as the solvent was collected. Analysis: Explain any difference in the appearance of the solvent and ink, if measured the max temperature, compare the boiling points of the solvents. Paper Chromatography Method: 1. draw a pencil line across the chromatography paper, 1-2 cm from the bottom 2. use a pipette or capillary tube to add small spots of each ink to the line on the paper 3. place the paper into a container with a suitable solvent in the bottom 4. allow the solvent to move through the paper, but remove the chromatogram before it reaches the top 5. allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent Record in a table Analysis: Calculate Rf Value for each spot ► Compare the Rf values and colours of each spot in the inks. Describe the similarities and differences.