Chemistry revision

Chemistry revision

1. Purifying water

   • Water is purified by filtering it so that leaves and soil are removed. First it goes through a screen where the large pieces of dirt are cleared away. Then through a course filter and sedimentation. Finally it goes through a fine filter - then chloride is added. It is then used in homes, shops and factories.

2. Separating mixtures

   • Mixtures are two or more elements or compounds that are not chemically combined. All elements will kepp their properties (e.g. iron will still be magnetic). Mixtures can be separated by a physical process, It does not have to be a chemical reactions for them to separate.
   • Crystallisation is one way to get a soluable solid from a solution. For example, salt and water. If you leave the solution to evaporate, all that will be left is the salt crystals.
   • You can use Chromatography to separate a mixture.

3. Chromatography

   • Chromatography involves a stationary phase, which does not move and a mobile phase which does move.
   • In paper chromatography the stationary phase is the absorbant paper and the mobile phase is the solvent, often water.
   • Each component moves a different distance up the paper depending o it's attraction to the paper. If it is more attracted then it will not move as far.

4. Gas Tests

   • Hydrogen- A colourless gas. It combines violently with oxygen when ignited. To test for it you can mix it with air and will make a squeaky pop.
   • Chlorine- A green poisonous gas that bleaches dyes. You can test for it because it turns a damp indicator white.
   • Carbon Dioxide- A colourless gas. Can be tested because when bubbled through lime water turns the lime water cloudy.

5. Life Cycle Assessment (LCA)

   • The LCA is used to assess the environmental impact a product has pver it's lifetime.
   • They provide a way into seeing what products are best for the environment. E.g It will allow a company to decide weather to use aluminium cans or plastic bottles to cause minimum impact.
   • To carry out the LCA, scientists will measure the impact of:
     • Extracting raw materials
     • Processing the raw materials
     • Manufacturing the product
     • How the product is used
     • How the product is transported
     • How it is disposed

6. Reducing the use of resources

   • Materials like glass, metal and plastic are important for us to live. However, they must be used wisely and recycled whenever possible.
   • Recycling saves money and energy, makes sure natural resources are not used up unecasserily and reduces the amount of waste produced.
   • Metal, glass and plastic made from crude oil are produced from limited resources. Our supplies are finite.