Periodicity

• What are the solubility rules?

  - Ca(OH)₂ and CaSO₄ sparingly soluable with  BaSO₄ insoluable.

  -In hydroxides,up the group solubility increases.In the sulfates solubility increases down the group.
• What is Ca(OH)2 used for?

  'Slaked lime'-used to treat acidity in soil where crops grow as they need a PH closer to neutral to grow properly.
• What is Mg(OH)2 used for?

  'Milk of magnesia'-treats indigestion by removing excessive stomach acid.
• Name and write the equation(process) both hydroxides undergo.

  Neutralisation

  H+(aq)+OH−(aq)⇋H2O(l)
• What is Barium sulfate used for?

  'Barium Meal'-used to diagnose stomach problems-it coats the tissue then shows up on x-ray.It's not harmful as it's insoluable so won't dissolve in the body.
• What is Magnesium sulfate used for?

  'Epsom salt'-a mineral used to replace magnesium in the body to increase water in the intestines.

  Magnesium in the extraction of Titanium:

  TiCl4(g) + 2Mg(l)  Ti(s) + 2MgCl2(l)
• What are all the soluable salts?

  Group 1 salts,ammonium salts(chloride/ sulfate) and all nitrates.
• What is CaO used for and equation?

  As a flue gas removing SO2

  CaO(s)+SO2(g)+2H20(l)→CaSO3(s)+2H20(l)+CO2(g)
• Group 2 reaction with waterequation

  metal (s)+2H20(l)→metal hydroxide(aq)+H2(g)
• What is the exception to the group 2 reactions with water?

  Mg-reacts very slowly with cold water,so instead reacts with hot steam.

  Mg(s)+H20(g)→MgO(s)+H2(g)
• testing for sulfate ions

  1)Place magnesium sulfate solution into a test tube.Add equal vol of dilute HCl and barium chloride solution-.This gives a whte precipitate of BaSO4(solubility decreases down the group)
• Why do we acidify BaCl2?


  other anions e.g. carbonates will give the same result of a white precipitate if not acidified,but if acidified the carbonate precipitate will dissolve.
• Why don't we use sulfuric acid to acidify BaCl2

  The sulfuric acid itself would form a white precipitate since it contains SO4^2-.
• Why are halogens less reactive down the group?

  -oxidising power decreases down the group because of increased atomic radius and therefore increased shells.
• Oxidising ability of halogens:

  Oxidising power decreases down group 7 as it's harder to gain electrons as atoms get larger and there's more shielding.
• Fluorine-appearance+properties


  yellow gas.

  Very reactive

  reacts strongly with water.
• Chlorine


  -green gas

  -very reactive

  -toxic
• Bromine


  -brown/orange liquid

  -very easily forms orange vapour

  -often used as a solution in water
• Iodine


  -grey crystalline solid

  -very easily forms purple vapour

  -used in a solution as antiseptic

  -reactive+ toxic
• Chlorine reaction with water+what type of reaction

  disproportionation(other halogens reacts similiarly but slowly down group)-

  Cl2(g)+H2O(l)⇌HClO(aq)+HCl(aq) -1 to +1 0 to -1(oxidation states of chlorine increasing + decreasing).
• What is a disproportionation reaction?

  Halogen is reduced and oxidised at the same time.
• Why does the disproportionation reaction take place?

  When chlorine is used to purify water for drinking and swimming pools.It's also used for killing bacteria in water and making bleach.
• Reaction in sunlight


  2Cl2(g) + 2 H2O(l)→4HCl(aq) +O2(g)
• Problem with sunlight reaction

  Chlorine is rapidly lost from pool water in sunlight so that shallow pools need frequent addition of chlorine.
• Alternative to direct chlorination of swimming pools

  salt form of chlorine-NaClO

  NaClO +H2O⇌Na+ + OH- +HClO also a disproportionate reaction.
• In alkaline solution,this equilibrium moves to the left and the HClO is removed as ClO- ions.To prevent this from happening,swimming pools need to be slightly acidic.
• Half equation for halogens

  halogen + e- →halogen -

  halogens gain an electron when they work with other elements and become a -1 halide.
• Fluoride is the most powerful oxidising agent than bromide,chloride and iodide and therefore displaces them .
• The halogen that donates an electron is the reducing agent.The weaker oxidising agent=stronger reducing agent.
• Reducing ability increases down group 7
• Steps for a halogen displacement reaction:


  diatomic halogen +salt of halide e.g. NaCl →sodium compound with more oxidising agent + diatomic halogen as leaving group(one that is displaced).
• How can you tell the observation of a halogen displacement?

  Leaving group halogen
• Same halogen in compound and reacting with it =no reaction

  compound halogen + halogen reacting with it is less powerful in oxidising = no reaction.
• Displacement reaction for F2+ NaCl

  F2 + 2 NaCl→2NaF + Cl 2 (F displaces Cl) pale green solution observed as we make chlorine.
• How do you make an ionic displacement equation?

  Remove Na (as it is spectator ion)+ use raw ion e.g. F2 + Cl-→F+Cl2
• Why is silver nitrate used?


  Allows us to distinguish between halides(as they have similar colour precipitates) and identify them.
• Test with silver nitrate


  1 Dissolve halides in water to form an aqueous solution

  2.Add a few drops of acidified (nitric acid)silver nitrate. Halides react with it to form silver halides

  3. Add ammonia
• Why is nitric acid added before silver nitrate?


  To prevent any false positive results from carbonate ions precipitating out with silver ions..
• Ionic equation for halide ions + silver nitrate

  Ag + (aq) + X- (aq) -- Agx(s)
• Why is ammonia added after the silver nitrate test

  Dilute then concentrated ammonia is added to silver halide solution to determines which halide ion is present as the white,cream,yellow precipitates look similar in colour.