Chemistry

• Define ionic bond

  Strong electrostatic forces of attraction bewptween oppositely charged ions
• Covalent bond is formed when atoms of non-metallic elements share electrons so as to achieve the stable electronic configuration of a noble gas to form molecules.
• define a covalent bond

  It is electrostatic forces attraction between the 2 positively-charged nucleI and the pair of negatively-charged electrons they share.
• Substances with simple molecular structure have low melting and boiling points because little energy is needed to overcome the weak intermolecular forces of attraction between the simple molecules.
• Substances with Simple molecular structures are unable to conduct electricity in any state as molecules are electrically neutral hence there are no mobile ions or free electrons to conduct electricity
• Substances with simple molecular structures are generally insoluble in water but soluble in organic solvents like ethanol, petrol and turpentine. Except for hydrogen chloride and ammonia that dissolve in water to form acids or alkalis.
• What is a characteristic of the melting and boiling points of compounds with a giant ionic structure?

  They have high melting and boiling points and usually exist as solids at room temperature and pressure.
• Why do compounds with giant ionic structures have high melting and boiling points?

  Because a large amount of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely-charged ions.
• What type of bonding do compounds with giant ionic structures exhibit?

  They exhibit ionic bonding and have a giant ionic structure.
• Why are ionic compounds unable to conduct electricity in the solid state?

  Because the ions are in fixed positions and cannot move around to conduct electricity.
• In which states can ionic compounds conduct electricity?

  They can conduct electricity in the molten and aqueous states.
• What happens to ionic compounds when they are dissolved in water?

  Water molecules can separate the positive ions from the negative ions, allowing them to move freely.
• How does the structure of ionic compounds affect their electrical conductivity in different states?

  In solid state, ions are fixed and cannot move, while in molten or aqueous states, ions are mobile and can conduct electricity.
• What is the role of water molecules in the solubility of ionic compounds?

  Water molecules weaken the attractive forces between ions, allowing them to separate and dissolve.
• What are the physical properties of compounds with a giant ionic structure?

  • High melting and boiling points
  • Usually exist as solids at room temperature and pressure
  • Unable to conduct electricity in solid state
  • Conduct electricity in molten and aqueous states
  • Mostly soluble in water
• Evidence of a chemical reaction

  • release of a gas (effervescence)
  • change in temperature
  • change in colour
  • energy released in the form of light and sound
  • formation of precipitate
• Polyatomic ions

  Sulfate SO4 2-

  Hydroxide OH-

  Carbonate CO3 2-

  Nitrate NO3-

  Phosphate PO4 3-

  Ammonium NH4+
• Methane

  CH4
• Ammonia gas


  NH3
• Hydrochloric acid

  HCL
• Sulfuric acid

  H2SO4
• Carbonic acid


  H2CO3
• Nitric acid

  HNO3
• Acids only show acidic properties when dissolved in water and produce hydrogen ions H+
• Bases include

  • metal oxide
  • metal hydroxide (alkali)
  • ammonia solution
• A salt is an ionic compound formed with positive ion from base and negative ion from acid
• What colour does litmus paper turn if solution is acidic?

  Red
• What colour does litmus paper turn if solution is alkaline?

  Blue
• at what ph does methyl orange change colour?

  ph4
• How to test for an acid? Using universal indicator?


  Add a few drops of universal indicator into solution. If solution turns red/orange/yellow, solution is acidic. If solution turns blue/violet, solution is alkaline.
• Test for an acid using acid + metal method

  Add a piece of metal to the solution, (eg magnesium). Effervescence will be observed and a colour less gas will be given off. Test the gas with a lighted splint. If splint is extinguished with a pop sound, gas is hydrogen and solution is an acid.
• Test for acid using carbonate.

  Add a carbonate into solution, eg sodium carbonate. Effervescence will be observed and a colour less gas will be given off. Bubble the gas into limewater, a white precipitate will be formed in the limewater. This shows that the gas is carbon dioxide and solution is an acid.
• Test for an alkali

  Add ammonium chloride into solution, or any ammonium salt, and warm the mixture. A pungent gas will be given off. Test the gas with a piece of moist red litmus paper and the litmus paper will turn blue. This shows that gas is ammonia and solution is an alkali.
• Why is the reaction between an acid and a base not the best way to test for acids and alkalis?

  There is no visible change that takes place immediately during neutralization.
• Acid + reactive metal >> Salt + hydrogen
• Acid + carbonate >> salt + water + carbon dioxide
• Acid + base >> salt + water
• Ammonium salt + alkali >> Ammonia gas + water + salt
• What is the phosphorus ion?

  Phosphide P3-
• Metallic atoms tend to lose electrons to achieve a full valence shell and become cations.