Acids and bases

• pH scale


  Measure of how acidic or alkaline a solution is, ranging from 0 to 14 with low numbers being most acidic and high numbers being most alkaline
• Neutral pH is 7, neither acidic nor alkaline
• Acidic substances


  • Stomach acid (pH 2)
  • Acid rain (pH 4)
• Alkaline substances


  • Washing up liquid (pH 9)
  • Bleach (pH 12)
• Measuring pH


  1. Using indicator (changes color depending on pH)

  2. Using pH probe and meter (electronic measurement)
• Acid


  Substance that forms aqueous solutions with pH less than 7, releases hydrogen ions in water
• Base


  Substance with pH greater than 7
• Alkali


  Soluble base that forms a solution with pH greater than 7, forms hydroxide ions in water
• Neutralization reaction


  Acid + base → salt + water
• Common acids


  • Hydrochloric acid
  • Sulfuric acid
  • Nitric acid
• Common bases


  • Sodium hydroxide
  • Calcium carbonate
• pH scale


  0-14, can be used to classify solutions as strongly acidic (0-3), weakly acidic (4-6), neutral (7), weakly alkaline (8-10) and strongly alkaline (11-14)
• Universal indicator


  Used to measure the approximate pH value of an aqueous solution
• The colours shown are those when using universal indicator
• Litmus


  Acid turns red, neutral stays purple, alkali turns blue
• Red and blue litmus paper

  Red in acid, yellow in alkali
• Methyl orange


  Colourless in acid, pink in alkali
• Phenolphthalein


  Colourless in acid, pink in alkali
• Acids


  Proton (H+) donors, source of hydrogen ions H+
• Bases


  Proton (H+) acceptors, can neutralise acids
• Bases


  • Metal oxides e.g. Magnesium Oxide, MgO
  • Metal hydroxides e.g. Magnesium hydroxides, Mg(OH)2
  • Ammonia, NH3
• Alkalis


  Bases which dissolve in water, source of hydroxide ions, OH-
• Alkalis


  • Sodium hydroxide, NaOH
  • Magnesium hydroxide, Mg(OH)2
• Acids in aqueous solution are a source of hydrogen ions (H+) and alkalis in an aqueous solution are a source of hydroxide ions (OH-)
• Neutralisation


  Acid + Base → Salt + Water
• Salts


  Formed when a base reacts with an acid
• Naming salts


  First half comes from the metal in the base, second half comes from the acid name
• Soluble salts


  • All sodium, potassium, ammonium salts
  • All nitrates
  • All chlorides, except silver chloride and lead(II) chloride
  • All sulfates, except barium sulfate, calcium sulfate and lead(II) sulfate
  • Sodium carbonate, potassium carbonate, ammonium carbonate
  • Lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide
• Insoluble salts


  • All carbonates, except sodium, potassium and ammonium carbonates
  • All hydroxides, except lithium, sodium, potassium and calcium hydroxides
• Preparing a pure, dry sample of a soluble salt from an insoluble reactant

  1. Copper oxide + sulfuric acid → copper sulfate + water

  2. Gently warm the acid over a hot water bath

  3. Add an excess of copper oxide to the warmed acid

  4. Stir the reaction mixture with a glass rod

  5. Filter the reaction mixture to remove any unreacted copper oxide

  6. Heat the filtrate gently using a water bath until it becomes saturated

  7. Filter out the blue copper sulfate crystals

  8. Place the crystals on filter paper and leave to dry slowly in a warm oven
• Neutral substances, such as water, have pH values equal to 7.
• pH scale


  0-14, can be used to classify solutions as strongly acidic (0-3), weakly acidic (4-6), neutral (7), weakly alkaline (8-10) and strongly alkaline (11-14)
• Universal indicator


  Used to measure the approximate pH value of an aqueous solution
• The colours shown are those when using universal indicator
• Litmus


  Acid turns red, neutral stays purple, alkali turns blue
• Red and Blue litmus paper

  Red in acid, yellow in alkali
• Methyl orange


  Colourless in acid, pink in alkali
• Phenolphthalein


  Colourless in acid, pink in alkali
• Acids


  Proton (H+) donors, source of hydrogen ions H+
• Acids


  • Hydrochloric acid (HCl), Sulfuric acid (H2SO4), Nitric acid (HNO3)