C5

• acids release positive H ions when dissolved in water: 3 main acids - sulfuric acid, nitric acid, and hydrochloric acid
• alkalis release OH negative ions when dissolved in water
• pH scale is a measure of alkalinity and acidity
• *solutions with a pH of <7 are acidic

  *solutions with a pH of >7 are alkaline

  *solutions with a pH = 7 are neutral
• universal indicator tells the approximate pH of solution - electronic pH probes give exact pH
• red = strongly acidic, yellow = lowly acidic, green = neutral, blue = lowly alkaline, purple = strongly alkaline
• pH scale us how many positive hydrogen ions in a solution; the more are present, the lower the pH; an increase of 1 on pH scale = decrease 10x number of hydrogen ions
• sulfuric, nitric, and hydrochloric acid are strong acids, meaning that when dissolved in water every molecule splits into ions
• ethanoic, citric, and carbonic acid are weak acids, meaning that only some molecules split into ions when dissolved in water
• Concentration tells us how much of a substance there is dissolved in water - more concentrated acids have lots of acid in a small volume of water, less concentrated acids have little acid in a large volume of water
• • acid + metal = salt
  • salt is a compound where H from an acid has been replaced by a metal e.g. nitric acid + sodium = sodium nitrate (HNO3 + Na = NaNO3)
• acid + (some)metals = salt + hydrogen gas
• acid + metal hydroxide = salt + water
• acid + metal oxide = salt + water
• acid + metal carbonate = salt + water + carbon dioxide
• Redox:

  • if metal loses electrons (gains oxygen) then is oxidised
  • if hydrogen gains electrons then is reduced
• bases neutralise acids to form water in neutralisation reactions
• some metal hydroxides dissolve in water to form alkaline solutions
• some metal oxides do not dissolve in water - they are bases, not alkalis
• Required Practical Crystallisation:

  • choose correct acid and base to produce salt
  • put some dilute acid into a flask and gently heat with a Bunsen burner
  • add a small amount of base and stir
  • add an excess of the base until no more reacts
  • filter with funnel and filter paper to remove unreacted base
  • put remaining solution in evaporating basin
  • heat until half of solution evaporates
  • salt crystals will be left behind
• REQUIRED PRACTICAL on making copper sulfate:

  • add insoluble copper oxide to sulfuric acid and stir
  • warm gently
  • solution turns blue as reaction occurs, showing copper sulfate is being formed
  • excess black copper oxide can be seen
  • when reaction is complete, filter solution to remove excess copper oxide
  • evaporate only half of water so copper sulfate crystals start to form
  • let other half of water slowly evaporate by itself: this gives larger crystals