chem acids bases and salts

• pH scale


  0-14, measures acidity or alkalinity of a solution, measured using universal indicator or pH probe
• pH less than 7

  Acidic, the lower it is, the stronger the acid
• pH more than 7

  Alkaline/basic, the higher, the stronger the alkali
• pH decreases by one unit


  H+ concentration of solution increases by a scale factor of 10
• Alkali


  A base that dissolves in water
• Acid and alkali properties

  • Acids release hydrogen ions (H+) in solution
  • Strong acids completely dissociate to release H+ ions (hydrochloric, nitric, sulfuric)
  • Weak acids partly dissociate to release H+ ions (ethanoic, citric, carbonic)
  • Alkalis contain hydroxide ions (OH-)
  • Strong bases fully dissociate to release OH- ions (sodium hydroxide, potassium hydroxide)
  • Weak bases partly dissociate to release OH- ions (ammonia, ammonium hydroxide)
• Dilute/concentrated


  Refers to the amount of substance present, the number of moles of that acid/base in solution
• Weak/strong


  Refers to the degree of ionisation of the acid and base, how readily the acid releases H+ ions or the base releases OH- ions
• Reaction of dilute acid with metals

  Acid+metal-> salt+hydrogen
• Reactivity series


  Shows the relative reactivities of different metals
• Neutralisation of dilute acids

  1. Acid+alkali-> salt+ water

  2. Acid+ base->salt+water

  3. Acid+ metal carbonate->salt+water+carbon dioxide
• Examples of alkalis


  • Soluble metal hydroxides
• Examples of bases


  • Insoluble hydroxides
• Salt produced


  Depends on acid used- positive ions in base alkali/ carbonate
• Types of salts


  • Chlorides (from hydrochloric acid)
  • Nitrates (from nitric acid)
  • Sulfates (from sulfuric acid)
• Sodium oxide+hydrochloric acid


  Sodium chloride+ water
• Potassium carbonate+ nitric acid

  Potassium nitrate+water+ carbon dioxide
• Preparing soluble salts


  1. Measure a set volume of acid

  2. Heat the acid gently

  3. Add the chosen base in excess

  4. Filter excess base

  5. Heat salt solution to evaporate water

  6. Leave to rest- evaporate slowly- crystals of salt form
• Preparing insoluble salts


  1. React 2 solutions- contain ions of desired salts

  2. Solid precipitation of salt is produced

  3. Filter salt using filter paper

  4. Wash with distilled water leave salt to dry
• Titrations


  1. Add acid to burette using funnel- record start volume

  2. Add known volume of alkali to a conical flask& few drops of indicator

  3. Place conical flask on white tile- see colour change

  4. Turn tap of burette to slowly add acid to alkali until reach neutralisation point- indicator changes colour

  5. Repeat until get concordance titres- within 0.1cm3 of each other

  6. Calculate volume of acid- called titre

  7. Use concordance results to calculate mean titre
• Indicator- pink-alkali, Colourless- acidic
• Chemical tests


  1. Carbon dioxide gas- bubble the gas through limewater- turn milky cloudy if present

  2. Carbonates- react with dilute acids- create carbon dioxide. Gas bubble thru limewater- goes cloudy

  3. Sulfate ions- add dilute hydrochloric acid followed by barium chloride solution. White precipitate form sulfate ions are in solution
• neutral solutions have equal amounts of H+ and OH-
• basic solutions have more OH- than H+
• acidic solutions have more H+ than OH-