Chemistry 5.2

• pH level scale


  Used to identify the difference between an acid and an alkali
• Indicators


  Substances that change colour when added to acidic or alkaline solutions
• Indicators


  • Universal indicator
  • Litmus
• pH level


  • Ranges from 0-14
  • Solution less than 7 is acidic (red, orange, yellow, light green)
  • Solution with 7 is neutral (green)
  • Solution more than 7 is alkaline (dark purple, blue, green)
• Acid


  When dissolved in water, they release H+ ions
• Acids


  • Hydrochloric acid
  • Sulfuric acid
  • Nitric acid
• Alkali


  When dissolved in water, they release OH- ions
• Alkali


  • Sodium hydroxide (NaOH)
• Acid reactions


  1. Acid + Metal -> Salt + Hydrogen

  2. Acid + Metal Oxide -> Salt + Water

  3. Acid + Metal Hydroxide -> Salt + Water

  4. Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide
• Salt


  An ionic compound resulting from a neutralisation reaction
• To test for hydrogen, use a burning split
• To test for carbon dioxide, pass it through limewater which turns cloudy
• Acid names


  • Hydrochloric acid - Chloride
  • Nitric acid - Nitrate
  • Sulfuric acid - Sulfate
• Neutralisation practical


  1. Step 1: Warm acid and add excess metal oxide/carbonate

  2. Step 2: Filter to remove insoluble solid, leaving salt and water solution

  3. Step 3: Evaporate solution to leave behind salt crystals
• Excess metal oxide/carbonate is added to ensure all acid is dissolved
• Acid-alkali titration


  1. Step 1: Measure volume of alkali

  2. Step 2: Add indicator to alkali

  3. Step 3: Fill burette with acid, note starting volume

  4. Step 4: Slowly add acid to alkali, stop at end point (colour change)

  5. Step 5: Note volume of acid used to neutralise alkali

  6. Step 6: Repeat for more results
• If volume of acid = volume of alkali, they have same concentration (1:1 ratio)
• If more acid is needed, alkali has higher concentration, acid has lower concentration
• If less acid is needed, acid has higher concentration, alkali has lower concentration
• Test for sulfate ions


  Add barium chloride - solution turns cloudy (white precipitate of barium sulfate forms)