Chapter 8

• Define reducing agent

  •Readily donates electrons

  •Substance that is oxidised
• Why are group 2 elements known as alkaline earth metals?

  Group 2 metal hydroxides have alkaline properties
• What is formed when a group 2 metal reacts with oxygen?

  a metal oxide with the general formula CaO
• What is formed when a group 2 metal reacts with water?

  an alkaline metal hydroxide with the general formula Ca(OH)2 and hydrogen gas
• Does reactivity increase or decrease down group 2?

  increases down group 2
• What is formed when a group 2 metal reacts with an acid?

  a salt and hydrogen
• Describe the link between reactivity and ionisation energy

  Ionisation energies decrease down the group as attraction between the nucleus and outer shell electrons decreases due to an increasing atomic radius and electron shielding. This makes it easier to lose electrons, thus reactivity increases down the group.
• Why are alkaline solutions produced when metal oxides react with water?

  OH- ions are released, forming alkaline solutions of group 2 metal hydroxides
• Does the solubility of group 2 hydroxides increase or decrease down the group?

  Increases down the group. The resulting solutions contain more OH- ions so are more alkaline
• How are group 2 compounds used in agriculture?

  Calcium hydroxide is added to fields as lime to increase pH of acidic soils. It neutralises the acid in soil, forming water.

  
  

  Ca(OH)2 + 2H+ = Ca2+ + 2H2O
• How are group 2 compounds used in medicine?

  Group 2 bases are used as antacids in treating indigestion.

  Mg(OH)2 + 2HCl = MgCl + 2H2O

  CaCO3 + 2HCl = CaCl2 + H2O + CO2
• What group are the halogens in?

  Group 7
• What structures do halogens form when solid?

  Lattices with simple molecular structures
• Describe and explain the boiling points of group 7

  Down the group, elements have more electrons so have stronger induced dipole-dipole interactions. More energy is required to break these intermolecular forces. Therefore, boiling point increases down group 7.
• Are halogens oxidising or reducing agents?

  oxidising agents
• Describe what happens in a halogen-halide displacement reaction

  The reactivity of halogens decreases down the group. The solution of halogen is added to aqueous solutions of other halide. If the halogen is more reactive than the halide present, the halogen displaces halide from solution and solution changes colour.
• What is added to solutions of iodine and bromine to distinguish between them?

  an organic non-polar solvent (e.g. cyclohexane)
• State the colour changes in halogen-halide displacement reactions

  Chlorine + Bromide = Orange

  Chlorine + Iodide = Violet

  Bromine + Iodide = Violet
• What element is reduced when chlorine reacts with bromide ions?

  Chlorine
• Why are fluorine and astatine not considered in halogen-halide displacement reactions?

  Fluorine is very reactive and reacts with most substances it comes in contact with.

  Astatine is very rare and radioactive.
• Describe the trends in reactivity and oxidation ability down the group

  Down group 7, atomic radius increases and there are more inner shells so electron shielding also increases. There is less nuclear attraction to capture an electron from another species so reactivity decreases down the group. Halogens become weaker oxidising agents down the group.
• What is disproportionation?

  A redox reaction in which the same element is both oxidised and reduced
• Describe and explain the reaction of chlorine with water

  Chlorine is used in water purification. When chlorine is added to water, disproportionation takes place.

  Cl2 + H2O = HClO + HCl
• How are bacteria killed when chlorine reacts with water?

  Bacteria are killed by chloric (1) acid and chlorate (1) ions. Chloric (1) acid acts as a weak bleach
• Describe and explain the reaction of chlorine with cold dilute aqueous sodium hydroxide

  If water contains sodium hydroxide, more chlorine dissolves and a disproportionation reaction takes place.

  Cl2 + 2NaOH = NaClO + NaCl + H2O

  There is a large concentration of ClO- ions from sodium chlorate (1). NaClO is used as a bleach.
• What are the benefits of using chlorine in water purification?

  Makes water safe to drink, kills bacteria and prevents diseases from breaking out.
• What are the risks of using chlorine in water purification?

  It is an extremely toxic gas, it is a respiratory irritant, it is fatal in large concentrations and can react with organic hydrocarbons to form chlorinated hydrocarbons, which can cause cancer.
• How can the reducing ability of halide ions be tested?

  Can be shown by reactions with sulfuric acid, which is a strong oxidising agent.

  Cl ions not powerful enough to reduce H2SO4

  Br ions more powerful; can reduce H2SO4 to SO2

  I ions even more powerful; can reduce SO2 to S which is further reduced to H2S
• State and explain the correct order for carrying out tests for anions

  1) Carbonate

  2) Sulfate

  3) Halides
• Describe and explain the carbonate test

  1) In a test tube, add dilute nitric acid to solution to be tested.

  2) If bubbles are present, the compound could be a carbonate.

  3) To prove that the gas is carbon dioxide, bubble the gas through limewater. If it is CO2, the solution will form a white precipitate.
• What are the positive results of the carbonate test?

  Bubbles when nitric acid is added. When the gas is bubbled through limewater, the CO2 will form a white precipitate.
• Describe and explain the sulfate test

  1) Add aqueous barium chloride to solution to be tested in a test tube.

  2) If the sulfate ions are present, a white precipitate of barium sulfate will be formed.

  3) Most sulfates are soluble in water; barium sulfate is very insoluble.
• What are the positive results of the halide test?

  Chloride= white precipitate, soluble in dilute NH3

  Bromide= cream precipitate, soluble in concentrate NH3

  Iodide= yellow precipitate, insoluble in concentrate NH3
• How can you analyse a mixture of ions?

  On the same solution...

  1) Continue adding HNO3 until bubbling stops in carbonate test. This ensures all carbonate ions are removed.

  2) Add an excess of Ba(NO3)2 to solution left from carbonate test in the sulfate test. Filter remaining solution. Sulfate ions will precipitate out as barium sulfate.

  3) To solution left, add AgNO3. Add NH3 to confirm what halide you have. Any CO3 2- ions and SO4 2- ions have already been removed. Any precipitate must involve halide ions.
• How can you test for ammonium ions?

  1) Aqueous sodium hydroxide is added to solution of ammonium ion.

  2) Ammonia gas is produced, although there are no gas bubbles as it is very soluble in water.

  3) Warm the mixture to release ammonia gas.

  4) Test the gas with moist indicator paper. Ammonia is alkaline so will turn the paper blue.