Analysis

• In chemistry, a pure substance is a single element or compound that is not mixed with any other substance
• Pure substances always melt and boil at specific temperatures
• Impure substances contain more than one type of element / compound in a mixture
• Formulations are mixtures that have been prepared using a specific formula
• Formulations are made from precise amounts of different components, and each component has a particular function
• techniques used to separate substances include filtration, distillation, crystallisation and chromatography
• Chromatography is used to separate different substances in a mixture to identify them
• Paper chromatography is specifically used to separate different dyes in an ink
• In paper chromatography, the first step is to draw a baseline in pencil near the bottom of a piece of filter paper and add the ink sample above it
• When doing chromatography with a pure substance, it won't separate out and will show a single spot on the chromatogram with a specific rf value
• flame tests

  A) lithium

  B) sodium

  C) posassium

  D) calcium

  E) copper

  
• anion is an ion with a negative charge
• cation is an ion with a positive charge
• tests for gases:

  • hydrogen- lit splint will burn with a squeaky pop
  • oxygen - relight a glowing splint
  • chlorine - bleaches damp litmus paper white
  • carbon dioxide - makes lime water cloudy
• A formulation is a mixture that has been designed as a useful product
• Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.

  Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
• Chromatography can be used to separate mixtures and can give information to help identify substances. Separation depends on the distribution of substances between the phases.

  
  

  the 2 phases of chromatography are the stationary phase and the mobile phase

  
• in chromatography the substances that are more soluble in the mobile phase or less attracted to the stationary phase move further
• Calculating Rf values

  A) dye

  B) solvent

  
• Carbonates react with dilute acids to form carbon dioxide gas. Carbon dioxide can be identified with limewater, which will turn cloudy if there are carbonate ions present
• Test for sulfates - add dilute hydrochloric acid and barium chloride to solution. If sulfate ions are present a white precipitate will form.
• Sodium hydroxide solution can be used to identify positively charged ions (cations)
• Identifying metal ions with sodium hydroxide solution

  1. Add sodium hydroxide solution

  2. Form white precipitates with aluminium, calcium and magnesium ions

  3. Aluminium hydroxide precipitate dissolves in excess sodium hydroxide
• Identifying metal ions with sodium hydroxide solution

  1. Add sodium hydroxide solution

  2. Form coloured precipitates with copper(II), iron(II) and iron(III) ions

  3. Copper(II) forms blue precipitate

  4. Iron(II) forms green precipitate

  5. Iron(III) forms brown precipitate
• testing for anions- for these 3 add silver nitrate and nitric acid to the solution:

  A) chloride

  B) bromide

  C) iodide

  
• to test for carbonate (anion) add dilute acid. positive result- carbon dioxide formed which can be a test for limewater
• sulfate test- add barium chloride

  positive result- white precipitate
• name for a negative ion?

  anion
• name for a positive ion?

  cation
• testing for cations:

  copper(Cu2)- blue precipitate

  iron(Fe2)- green precipitate

  iron(Fe3)- brown
• Testing for cations

  calcium and magnesium-adding excess sodium hydroxide solution, white precipitate does not dissolve
• testing for aluminium(cation)- addition of excess sodium hydroxide, white precipitate forms and dissolves