Chemistry Y7 C4

• Acidic foods


  Taste sour
• Some vegetables


  Contain alkali and taste bitter
• Citrus fruits


  Contain acid and taste sour
• Never taste any chemical in a science lab!
• Many alkalis


  Feel soapy
• Many cleaning products are alkaline
• Common acids


  • Vinegar (ethanoic acid or acetic acid)
  • Fertilizer (nitric acid)
  • Lemons (citric acid)
  • Stomachs (hydrochloric acid)
  • Car batteries (sulfuric acid)
• Common alkalis


  • Used to whiten clothes
  • Found in glass cleaner
  • Used to make soap and clear clogged drains
  • Used to make bread and cakes rise
• Corrosive


  Chemicals that can eat away skin and metal
• Strong acids and alkalis are corrosive
• Alkalis are sometimes referred to as caustic instead of corrosive
• Wear goggles, use gloves and a lab coat, and don't run when handling corrosive chemicals
• Dilute


  Fewer particles of acid or alkali in the solution
• Concentrated


  More particles of acid or alkali in the same volume of solution
• Calculating concentration of a solution


  Concentration = mass in grams / volume of water in litres or cm3
• Higher concentration of hydrochloric acid


  More corrosive
• pH


  Potential of Hydrogen, shows how acidic or alkaline a substance is
• pH range and descriptions


  • 1-3: strong acid
  • 4-6: weak acid
  • 7: neutral
  • 8-10: weak alkali
  • 11-14: strong alkali
• Lower pH of hydrochloric acid

  More dangerous
• Higher pH of sodium hydroxide

  More dangerous
• pH indicator


  Changes colour to tell if a substance is an acid or alkali, and how acidic or alkaline it is
• Litmus paper


  Blue turns red for acids, red turns blue for alkalis

  
• Universal indicator


  Changes different colours to indicate how acidic or alkaline a substance is
• Base


  Neutralises an acid
• Alkali


  A soluble base
• Soluble


  Able to dissolve
• Neutralising an acidic solution

  Add a base or alkali until the pH reaches 7
• Neutralising an alkaline solution

  Add an acid until the pH reaches 7
• Situations needing neutralisation


  • Heartburn (too much stomach acid, take antacids)
  • Acid rain (add lime to lakes)
  • Adjusting soil pH for crops
• Acids are compounds, not elements
• All acids contain hydrogen
• Salt


  A compound formed when the hydrogen atoms of an acid are replaced by metal atoms
• Making a salt


  React a metal or a base with an acid
• Reaction of metal with acid


  Metal + acid → salt + hydrogen
• Reaction of base with acid


  Base + acid → salt + water
• Naming salts


  First name is the metal, second name depends on the acid (chloride, sulfate, nitrate)
• Steps to make magnesium chloride

  1. Add magnesium to hydrochloric acid, stir, repeat

  2. Heat solution to evaporate most water

  3. Filter to separate leftover magnesium

  4. Let last bits of water evaporate for crystals
• Balanced formula equation: Mg + 2HCl → MgCl2 + H2