chemistry

• Water purification methods


  1. Sedimentation

  2. Centrifugation

  3. Filtration

  4. Extraction
• Sedimentation


  A suspension in which water is mixed with soil. The substance with the greatest density settles to the bottom
• Centrifugation


  Speeds up sedimentation by flinging the substance with the greatest density to the bottom
• Filtration


  Separates larger particles from water molecules by passing through a filter
• Extraction


  Uses a solvent to dissolve one part of the mixture while leaving the other part undissolved
• Percent yield = actual yield ÷ theoretical yield × 100%
• Evaporation


  Uses the difference in boiling point to separate substances in a solution. The solvent evaporates leaving the solid behind
• Distillation


  Uses the difference in boiling point to separate substances in a solution. The substance with the lowest boiling point boils first and condenses into a collecting vessel
• Distillation


  1. The substance with the lowest boiling point will boil first

  2. Temperature of the vapour can be read on the thermometer

  3. Vapour is collected in a cooler where it condenses

  4. The resulting liquid drips into a collecting vessel such as an Erlenmeyer flask

  5. The part of the solution that does not evaporate and remains in the flask is called the residue

  6. The collected liquid is called the distillate
• Distillation apparatus


  • Used in the distillation process
• Distillation of a mixture of alcohol and water

  1. First (mainly) the alcohol will evaporate and condense, followed by the water

  2. Temperature rise on the thermometer indicates the change from alcohol to water evaporation
• In some cases, it is not possible to collect each liquid separately in distillation if the boiling points of different liquids in a mixture are very close
• In the distillation of crude oil, the distillate is usually a mixture of liquids rather than a pure substance
• Adsorption


  1. Separation method where toxic gases attach to a solid in a gas mask, allowing clean air with oxygen to pass through

  2. Used in the production of drinking water to remove undesired dissolved colourants and flavourings

  3. Substances are bound to the surface of the adsorption agent while others in the mixture are not absorbed

  4. Difference in adhesion of substances in the mixture is utilized
• Adsorption agent


  • Activated charcoal, also known as Norit
• The Commodities Act specifies the requirements foodstuffs must meet and mandates the manufacturer to state the product composition on the label
• Chromatography


  1. Important method for determining product composition in laboratories

  2. Different forms include paper chromatography, thin layer chromatography, and gas chromatography
• Paper chromatography


  1. Substances are separated based on solubility and adhesion by applying them to a baseline on paper and allowing a solvent to move up through the paper

  2. Result is a chromatogram showing the separation of substances based on their movement speed
• Chromatography


  Separation method that uses the difference in solubility and adhesion
• Every substance will have an Rf-value at a certain temperature, using a certain stationary phase and solvent
• Determining Rf-value of a substance


  Measure the distance the substance travelled from the base line on a chromatogram (A), measure the distance the solvent front reached from the base line (B), Rf-value is A÷B
• Thin layer chromatography


  Uses a glass or plastic plate covered with silica gel as the stationary phase and a solvent as the mobile phase
• Gas chromatography


  Takes place in a long thin tube called a column, with a gas as the mobile phase and a stationary phase inside the column. Substances in the mixture are separated based on their binding to the stationary phase, with each substance having a specific retention time
• Solubility is the maximum number of grams that can dissolve in one litre of solvent at a certain temperature
• A saturated solution is one in which the maximum amount of substance is dissolved, while an unsaturated solution has less than the maximum dissolved
• When an unsaturated solution of a solid is evaporated, the solute precipitates at the bottom once the maximum solubility per mL of liquid is reached
• Solubility of solids and liquids increases as the temperature of the solution increases, but the solubility of gases decreases with increasing temperature