Chapter 11

• Physical change is a change where no new substances are formed, identity and composition of substance is unchanged. (Chemical change is opposite)
• Combustion, Oxidation, Thermal decomposition and neutralisation are chemical changes
• Combustion and oxidation need oxygen (thermal decomposition don’t need), thermal decomposition only have 1 reactant
• Effervescence occur when gas produced, lighted splint for hydrogen and limewater for carbon dioxide
• Copper, silver, gold and platinum are unreactive metals
• Alkaline ends with hydroxide, exception of aqueous ammonia.
• Must remember

  1. Acid + Reactive metal -> salt + hydrogen
  2. Acid + Carbonate -> Salt + water + carbon dioxide
  3. Acid + Oxide/hydroxide -> Salt + water (Neutralisation)
• Physical change

  • no new substances formed
  • change reversible
  • properties remain the same
  • melting, boiling, sublimation etc.
• Chemical change

  • one or more new substance formed
  • change irreversible
  • new substance have new set of properties
  • two or more substances chemically combine to form one or more new substances/ substance breaks down into two or more substances (decomposition)
• Chemical changes examples

  1. mixing
  2. heating (combustion and thermal decomposition, cooking )
  3. Exposure to light ( Photosynthesis, photograph turning yellow )
  4. Electrolysis ( Electroplating, coat with metal)
  5. Oxidation ( rusting, colour fading)
• Acid reactions

  1. Acid + reactive metals -> salt + hydrogen— effervescence, lighted splint neat, if extinguishes with ‘pop’ sound hydrogen is present.
• Acid reactions

  2. Acid + metal carbonates -> salt + water. carbon dioxide

  • effervescence, bubble gas in limewater, if white precipitate formed, carbon dioxide is present
• Acid reactions

  3. Acid + metal oxide/hydroxide -> salt + water

  • neutralisation
• Bases

  • metal oxides and hydroxides
  • Not all bases are alkalis, copper/magnesium oxide insoluble as have METAL
  • Soluble bases dissolve in water to form alkali
  • React with acid to form salt and water (diff with alkali)
• Alkali

  • name end with hydroxide
  • any base soluble in water
  • turn red litmus paper blue
• Acid

  • sour taste
  • recat with alkali, metal and carbonates
  • turns blue litmus red
• pH level

  • how acidic or alkaline a solution is
  • neatral (7) has no effect on both litmus papers
  • pH meter, electrical, dipped in solution and pH level show, more reliable and accurate
• Combustion

  • substance heated in presence of oxygen to form one or more new substances
• Oxidation

  • matter interacts with oxygen and gains it when undergoing chemical change
• Thermal decomposition

  • substance break into two or more simpler substance upon heating
• Neutralisation

  • acid mixed with alkali, bring to pH level 7
  • agriculture: excess acid from acid rain neutralised by adding calcium hydroxide (alkali)
  • toothpaste: neutralise acid in mouth, prevent decay
  • antacids: contain alkaline, neutralise excess acid in stomach, heal pain
• Chemical reactions

  • atoms rearrange to combine chemically to form new products
  • atom for reactant and product must be equal for balanced chemical equation