Chemical properties

• What is combustion?


  It is a chemical reaction in which a substance is heated in the presence of oxygen to form one or more new substances.
• What is usually given out during combustion?

  Heat and/or light.
• Combustion

  • The burning of hydrogen as a fuel for rockets: hydrogen + oxygen → water
  • Burning methane for cooking: methane + oxygen → carbon dioxide + water
  • Burning charcoal for grilling food: carbon + oxygen → carbon dioxide
• Complete combustion


  A combustion that takes place when a substance burns with a sufficient amount of oxygen, producing carbon dioxide
• Incomplete combustion


  A combustion that takes place when a substance burns with an insufficient amount of oxygen, producing carbon monoxide and/or soot
• Combustion is an important chemical reaction. In the world today, the burning of fuels such as petrol, natural gas and coal provides more than 90% of the energy needed for transport, industries, and homes.
• Thermal decomposition


  A single compound breaks into two or more simpler substances when it is heated
• Thermal decomposition examples

  • Decomposition of metal carbonates: calcium carbonate → calcium oxide + carbon dioxide
  • Decomposition of metal hydroxides: magnesium hydroxide → magnesium oxide + water
• Photosynthesis


  A chemical reaction that takes place in green leaves when they are exposed to light, where the chlorophyll in the green leaves traps sunlight to convert carbon dioxide and water into glucose and oxygen
• Photochemical degradation


  A chemical process in which a substance undergoes degradation or decomposition when exposed to light, particularly ultraviolet rays or visible light
• Electroplating


  A process used to coat the surface of an object with a layer of metal through a chemical reaction
• How to coat a layer of Y on the surface of X through electroplating

  1. Y (object to coat another object) is connected to the positive terminal of the battery

  2. X (object to be coated) is connected to the negative terminal of the battery

  3. The solution must contain Y particles

  4. As the electric current flows through the solution from Y to X, the Y particles will coat the surface of X layer by layer
• A Y-coated object is obtained through the electroplating process
• Oxidation


  A chemical reaction in which a substance gains oxygen. It can take place with or without combustion.
• Examples of oxidation that can be classified as combustion

  • hydrogen + oxygen → water
• Examples of oxidation

  • Formation of carbon dioxide during cellular respiration: glucose + oxygen → carbon dioxide + water
• Chemical change caused by mixing substances


  When two or more substances react chemically after mixing together, new substances will be formed with different chemical properties than the original substances
• Neutralisation


  Mixing acids with bases can initiate chemical reactions that produce new substances
• Common acids used in laboratory

  • Sulfuric acid (H2SO4)
  • Hydrochloric acid (HCl)
  • Nitric acid (HNO3)
• General properties of acids

  • have a sour taste
  • turn blue litmus paper red
  • have a pH value less than 7
  • are corrosive
  • can conduct electricity
  • react with metals, carbonates and bases/alkalis
• Bases


  Substances that react with acids to produce salt and water
• Alkali


  A soluble base
• Some common bases and alkalis

  • Bases: Sodium oxide (Na2O), Sodium hydroxide (NaOH)
  • Alkali: Calcium oxide (CaO), Potassium hydroxide (KOH)
• Alkalis are common in our daily lives, such as in soaps, detergents, window cleaners, and indigestion tablets
• General properties of alkalis


  • They have a bitter taste
  • They have a slippery or soapy feel
  • They turn red litmus paper blue
  • They are corrosive
  • They can conduct electricity
  • They react with acids to produce salts and water
• Acids react with bases / alkalis to form salt and water
• Acids react with metals to produce salt and hydrogen
• How to confirm whether a reaction between an acid and metal has taken place


  1. Use a lighted splint to test for hydrogen gas produced from the reaction

  2. If the reaction has taken place, the presence of hydrogen will have the following observations: 1. A 'pop' sound is produced, 2. The lighted splint extinguishes
• Copper, silver, gold cannot react with acids
• Acids react with carbonate compounds to form salt, water and carbon dioxide
• How to test whether a reaction between an acid and carbonate has taken place


  1. Use limewater to test for carbon dioxide gas produced

  2. If the reaction has taken place, the presence of carbon dioxide will turn the limewater chalky
• pH values of acids and alkalis

  • Acids have pH values less than 7, the smaller the pH value the stronger the acid
  • Alkalis have pH values greater than 7, the larger the pH value the stronger the alkali
• Atoms form ions to achieve full outermost shell of the nearest stable noble gas configuration