Group 7

• Describe the standard stages of the first 4 halogens

  fluorine - pale yellow gas

  chlorine - pale green gas - poisonous at high concentrations

  bromine - brown-orange liquid - brown/oragne poisonous fumes

  iodine - shiny grey solid, but a purple gas

  • they are all toxic
• describe the trends in melting and boiling points down group 7

  increases down the group

  as molecules become larger, there are more electrons, so stronger van der waals forces between molecules

  more energy is needed to overcome the van der waals forces between molecules
• define oxidising agent

  electron acceptors
• define electronegativity

  the power of an atom to attract the bonding pair of electrons in a covalent bond towards itself
• What colour precipitate would the halide ions produce?

  Chloride - white

  bromide - cream

  Iodide - yellow
• why would the reaction between silver nitrate and potassium fluoride not produce a precipitate?

  because silver fluoride is soluble
• describe a method to test for halides

  metal halide must be in solution form - if it is in solid state, must dissolve in water

  add dilute nitric acid

  add silver nitrate solution

  since the colour precipitate produced are quite similar, further tests can be carried out to confirm the answer
• what further test would you do to test for silver chloride

  silver chloride forms a white precipitate

  the precipitate will dissolve in dilute ammonia
• what further test would you do to test for silver bromide

  silver bromide forms a cream precipitate

  the precipitate wont dissolve in dilute ammonia, but will dissolve in concentrated ammonia
• what further test would you do to test for silver iodide

  silver iodide forms a yellow precipitate

  the precipitate doesn’t dissolve in dilute or concentrated ammonia
• why do we need to add nitric acid?

  to remove hydroxide and carbonate ions which also produce precipitates and would therefore give a false positive result
• why can we not add hydrochloric acid?

  this would add extra chloride ions which would produce silver chloride precipitate and so give a false result
• which reaction does all halide ions go through when reacted with concentrated sulfuric acid

  goes through an acid base reaction

  acid is the proton donor

  base is the proton acceptor

  HCl is produced which forms misty white fumes

  also produces sodium hydrogensulfate

  the halide ion accepts a proton so it is a base
• which reaction do only some halide ions go through when reacted with concentrated sulfuric acid ?

  redox reaction - only if the halide ion is a powerful enough reducing agent

  as you go down group 7, the halide ions be come more powerful reducing agent

  this is because the outer shell electrons are lost more easily because its further from the nucleus and there is more shielding

  Bromide ions can reduce sulfate ion to sulfur dioxide only

  Iodide can reduce sulfate ion to all forms of sulfur
• Observation when concentrated sulfuric acid is added to fluoride ion

  — misty fumes

  — due to hydrogen fluoride being produced in an acid base reaction
• observation when concentrated sulfuric acid is added chloride ion

  — misty fumes

  — due to hydrogen chloride being produced in an acid base reaction
• observation when concentrated sulfuric acid is added to bromide ions

  — misty fumes

  — orange/brown fumes due to bromine forming

  — due hydrogen bromide being produced in an acid base reaction
• observation when concentrated sulfuric acid is added to iodide ions

  — misty fumes

  — purple vapour due to iodine forming

  — bad egg smell to hydrogen sulfide forming

  — yellow solid forms due to sulfur forming

  — due to hydrogen halide being produced in an acid base reaction
• give the chemical reaction of chlorine reacting with water

  CL2 + H2O ————> HClO + HCl

  — chloric acid and hydrochloric acid formed
• describe disproportionation

  — an element simultaneously oxidises and reduces

  so chlorine is simultaneously reducing and oxidising, changing its oxidation state constantly from 0 to -1 and -1 to 0
• what is chlorine used for?

  — purify drinking water and swimming pools to prevent diseases - kills bacteria

  — the benefits of health to water treatment outweighs the toxic effects

  — if a universal indicator is added, it’ll first turn red due to the acidity of both products, and then turn colourless due to HClO bleaching colour

  — the pale green is due to the chlorine
• state the chemical reaction of chlorine with water in sunlight

  2Cl2 + 2H2O ———-> 4HCl + O2

  pale green to colourless

  the same reaction occurs to the equilibrium mixture of chlorine water

  the greenish colour of chlorine water fades as the chlorine reacts and colourless oxygen forms

  sunlight decomposes chlorinated water so no chloric acid is made
• describe the reaction of halogens with cold dilute sodium hydroxide solution

  — chlorine, bromine and iodine will react with cold dilute NaOH

  — colour of solution will fade to colourless

  — a mixture of NaClO is used as bleach to kill bacterra

  — its a disproportionation reaction

  CL2 + 2NaOH ————> NaClO + NaCl + H2O
• describe the reaction of halogens with hot dilute NaOH solution

  — disproportionating occurs but the halogen that’s oxidised goes to a higher oxidation state
• Are halogens more oxidising or less oxidising going down the group?

  — less oxidising
• How is bleach made?

  — by a disproportionation reaction

  — mixing chlorine and sodium hydroxide forms sodium chlorate (I)

  2NaOH + Cl2 ———> NaClO + NaCl + H2O

  — chlorine has been simultaneously reduced and oxidised
• uses of sodium chlorate (I)

  — treating water

  — bleaching paper and fabrics

  — bleach
• Advantages of chlorinating drinking water

  — destroys microorganisms that cause disease

  — long lasting so reduces bacteria build up

  — reduces growth of algae that discolours water and can give it a bad taste
• disadvantages of chlorinating drinking water

  — chlorine gas is toxic and irritates the respiratory system

  — liquid chlorine causes severe chemical burns to the skin

  — can react with organic compounds present in water to make chloroplasts which can cause cancer
• Tests for group 2 ions

  — in a solid sample

  — they’re made int o solutions and sprayed on a bunsen, but can be difficult if the sample being tested for is insoluble

  — dip the nichrome wire in concentrated hydrochloric acid

  — dip into sample

  — place the loop into the blue Bunsen flame and observe the colour
• what are the test results for group 2 ions?

  — dark red : calcium

  — red : strontium

  — green : barium
• test for ammonium compounds

  add sodium hydroxide and gently heat

  if ammonium compound is present then ammonia gas will be produced

  use damp red litmus paper - ammonia will dissolve in the water and turn the litmus paper blue
• test for hydroxides

  hydroxides are alkaline and will turn red litmus blue

  — test doesn’t mean you will have hydroxides, red litmus turns blue for any alkali, so you need to do further tests
• tests for carbonates

  — add hydrochloric acid

  — hydrochloric acid will react with carbonates to make carbon dioxide gas

  — when bubbled through limewater it turns it cloudy
• test for sulfates

  — add hydrochloric acid to remove any carbonate ions

  — these could produce a precipitate so produce a false result

  — add barium chloride

  — you will see a white precipitate if there’s sulfates - this white precipitate is barium sulfate which is insoluble

  Ba 2+ + SO4 2- ————> BaSO4
• tests for ions in order

  — test for carbonates first

  — if no carbon dioxide produced, test for sulfates

  — if no white precipitate forms, test for halides, add silver nitrate solution and nitric acids (white/cream/yellow/conc/dilute ammonia)
• state why iodobutane is formed faster than iodobutane

  — C-I bond is weaker than C-Br bond
• Describe a series of tests that you can use to show that the solution contains ammonium sulfate

  — warm with NaOH

  — damp red litmus at the mouth of the tube turns blue

  — add barium chloride and hydrochloric acid

  — a white precipitate forms