CC8 Acids And Alkalis

• Acidity or alkalinity of a solution is measured on the pH scale ( 1-14).
• Indicators can tell us the pH of solution as they change colour depending on the pH.
• • Methyl orange – red in acid and yellow in alkali
• Litmus – red in acid and blue in alkali
• Phenolphthalein – colourless in acid and pink in alkali
• acids =

  • Acids produce hydrogen ions (H+) when they dissolve in water 
  • e.g. hydrochloric acid dissociates in water and splits into H+ and Cl- ions.
• alkalis =

  • Alkalis produce hydroxide ions (OH-) in water

  e.g. sodium hydroxide splits into Na+ and OH- ions when it dissolves.
• hydrochloric acid = HCl (aq)
• sulfuric acid = H2SO4 (aq)
• nitric acid = HNO3 (aq)
• sodium hydroxide = NaOH
• potassium hydroxide = KOH
• calcium hydroxide = Ca(OH)2
• • The higher the number of hydrogen ions (H+), the more acidic the solution, the lower the pH
• The higher the concentration of hydroxide ions (OH-) the more alkaline the solution and the higher the pH.
• • Neutral solutions, such as pure water, have a pH of 7 and contain low, equal, concentrations of hydrogen ions (H+) and hydroxide ions (OH-).
• concentration = mass/volume
• If the pH decreases by 1, the concentration of H+ ions increases by a factor of 10. (STRONGER ACID).
• If the pH increases by 1, the concentration of H+ ions decreases by a factor of 10. (WEAKER ACID).
• • Low pH = strong acids 

  Strong acids break up (dissociate) completely into ions when they dissolve in water. Lots of H+ ions in solution.
• • Higher pH = weak acids
  • They only partially dissociate into ions in solution. Fewer H+ ions in solution.
• A base is any substance that will react with acids to form a salt and water only.
• Bases that are soluble in water are called ALKALIS
• • Alkalis release hydroxide ions (OH-) when they are added to water. In a neutralisation reaction, hydrogen ions (H+) from the acid react with hydroxide ions from the alkali to form water:      H+(aq)  +  OH-(aq)  🡪  H2O(l)
• neutralisation - acid + base = salt + water
• A titration can give to a much more precise end point when carrying out a neutralisation reaction.
• To obtain a pure, dry sample of a salt with titration:

  1. Carry out a titration.

  2. Note the exact volume of acid needed to neutralise the alkali.

  3. Use the burette to add the correct volume without the indicator.

  4. Evaporate the water from the solution formed.
• metal + acid = salt + hydrogen
• acid + carbonate = salt + water + carbon dioxide
• oxidation is losing
• reduction is gaining
• hydrogen test = lit spill in gas, makes squeaky pop
• oxygen test = glowing spill in gas relights
• chlorine test = damp blue litmus turns red then bleaches white
• carbon dioxide test= turns limewater cloudy
• Compounds soluble in water


  • All common sodium, potassium, ammonium salts
  • All nitrates
  • Most chlorides
  • Most sulphates
  • Sodium, potassium ammonium carbonate
  • Sodium, potassium, ammonium hydroxide
• • insoluble in water = silver, lead chloride lead, barium, calcium sulfate most carbonates most hydroxides