GCSE | Chemistry /9/ Separate Chemistry II

• The test for any ion must be unique because if more than one ion gave the same result, you would never be able to know which specific ion it was
• Flame tests to identify ions in solids:

  • Lithium ion, Li+ (red)
  • Sodium ion, Na+ (yellow)
  • Potassium ion, K+ (lilac)
  • Calcium ion, Ca2+ (orange - red)
  • Copper ion, Cu2+ (blue - green)
  • Hold a sample on a wire in a roaring bunsen burner flame and observe the flame colour
• Tests to identify ions in solids or solutions using sodium hydroxide solution:

  • Aluminium ion, Al3+
  • White precipitate (dissolves when excess NaOH is added)
  • Calcium ion, Ca2+
  • White precipitate
  • Copper ion, Cu2+
  • Blue precipitate
  • Iron (II) ion, Fe2+
  • Green precipitate
  • Iron (III) ion, Fe3+
  • Brown precipitate
  • Ammonium ion, NH4+
  • Pungent-smelling gas is produced
  • Gas produced turns damp red litmus paper blue
• Chemical test for ammonia:

  • Makes damp red litmus paper turn blue
  • Forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it
• Tests to identify ions in solids or solutions:

  • Carbonate ion, CO3 2-, using dilute acid and identifying the CO2 evolved
  • Sulfate ion, SO4 2-, using dilute hydrochloric acid and barium chloride solution
  • Chloride ion, Cl-, bromide ion, Br-, iodide ion, I-, using dilute nitric acid and silver nitrate solution
• Core Practical: Identify the ions in unknown salts using the tests for the specified cations and anions

  • Tests from 9.2C, 9.3C, 9.4C, 9.5C
• Instrumental methods of analysis:

  • Accurate, sensitive, and rapid
  • Include gas chromatography and mass spectrometry
• Evaluate data from a flame photometer to determine the concentration of ions in dilute solution using a calibration curve and to identify metal ions by comparing the data with reference data

  • Sample is put into a flame and the light given out is passed through a photometer
  • Output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations
• Polyesters are formed when a monomer molecule containing two carboxylic acid groups is reacted with a monomer molecule containing two alcohol groups
• The dicarboxylic acid loses the OH group off of each COOH group
• The di-alcohol loses the H off of each OH group
• The remaining molecules join together to make a polyester
• A molecule of water is formed each time an ester link is formed
• The OH and H groups combine to make H2O
• Advantages of recycling polymers:

  • Reuse waste materials, better for the environment than burning or putting them in landfills
  • Saves crude oil, a finite resource
  • More economically viable instead of making more polymers
• Disadvantages of recycling polymers:

  • Difficult and expensive to first separate the different polymers, they need to be sorted into types
• DNA is a polymer made from 4 different monomers called nucleotides
• Starch is a polymer based on sugars
• Proteins are polymers based on amino acids
• Alcohols contain the functional group -OH
• The first 4 members of the alcohol series are methanol, ethanol, propanol, and butanol
• The functional group in alcohols is -OH
• The formulae of molecules of the carboxylic acids:

  • Methanoic acid: CHOOH
  • Ethanoic acid: CH3COOH
  • Propanoic acid: CH3CH2COOH
  • Butanoic acid: CH3CH2CH2COOH
• The functional group in carboxylic acids is -COOH
• Ethanol can be oxidized to produce ethanoic acid and this can be extended to other alcohols
• Ethanol can be produced by fermentation with yeast using renewable sources
• It is produced from carbohydrates, can be sugars from fruit or starch
• Mixture must be kept warm and under anaerobic conditions
• Glucose → ethanol + carbon dioxide
• Ethanol concentration is about 15% from fermentation, ethanol is separated from the reaction mixture using fractional distillation
• Water and ethanol solution are heated

  • Ethanol evaporates first, cools, then condenses
  • Water left evaporates, cools, then condenses
• Nanoparticles are 1-100 nanometers across and contain a few hundred atoms
• They have a high surface area to volume ratio
• Nanoparticles have different properties to the 'bulk' chemical they are made from
• Possible risks associated with some nanoparticulate materials:

  • Some worries that they may be harmful to health, enter the bloodstream and cause harm
  • Effects of nanoparticulate materials are unknown and this is worrying for some people as risks are not fully known
• Comparison of physical properties of glass, clay ceramics, polymers, composites, and metals
• Glass ceramics: transparent, hard, brittle, poor heat and electrical conductors

  • Clay ceramics: opaque, hard, brittle, poor heat and electrical conductors
  • Polymers: can be made transparent/translucent/opaque, poor heat and electrical conductors, can be tough or ductile
  • Metals: shiny, good heat and electrical conductors, hard, tough
• Explanation of why the properties of a material make it suitable for a given use and selecting materials appropriate for specific uses
• Different properties of materials are evaluated to determine suitability for certain uses

  • For example, metals are suitable for electrical cables because they are good electrical conductors and ductile, while polymers are unsuitable as they are poor electrical conductors