Chemistry

• Acid


  A substance that releases hydrogen ions (H+) when dissolved in water
• Alkali


  A substance that releases hydroxide ions (OH-) when dissolved in water
• Main acids


  • Hydrochloric acid (HCl)
  • Sulfuric acid (H2SO4)
  • Nitric acid (HNO3)
• Main alkalis


  • Sodium hydroxide (NaOH)
  • Magnesium hydroxide (Mg(OH)2)
  • Aluminium hydroxide (Al(OH)3)
• pH scale


  pH less than 7 is acidic, pH greater than 7 is alkaline, pH 7 is neutral
• pH ranges


  • Strong acid: pH 1-2
  • Weak acid: pH 3-6
  • Weak alkali: pH 8-10
  • Strong alkali: pH 11+
• Phenolphthalein


  Indicator that is colourless in acids and pink in alkalis
• Methyl orange


  Indicator that is orange in acids and yellow in alkalis
• Litmus


  Indicator that is purple, turns red in acids and blue in alkalis
• As pH decreases by 1


  Concentration of H+ ions increases 10 times
• At pH 7 there are no H+ or OH- ions, just water (H2O)
• Dilute


  Low concentration of H+ ions
• Concentrated


  High concentration of H+ ions
• Weak acid


  Partially ionises in water, producing few H+ ions
• Strong acid


  Fully ionises in water, producing many H+ ions
• Weak acid reacts slower with marble chips


  Produces less gas volume in 30 seconds
• To increase gas volume from weak acid

  Make the weak acid more concentrated
• To decrease gas volume from strong acid


  Make the strong acid more dilute
• Base


  Neutralises an acid, produces water
• Alkali


  Soluble base that neutralises an acid
• Acid-salt products


  • Chloride (from HCl)
  • Sulfate (from H2SO4)
  • Nitrate (from HNO3)
• Oxide reacts with acid

  Produces water
• Carbonate reacts with acid


  Produces carbon dioxide and water
• No oxide/carbonate reacts with acid


  Produces hydrogen
• Test for carbon dioxide

  Bubble gas through limewater, turns cloudy
• Test for hydrogen


  Bring a lit splint to the gas, makes a squeaky pop sound