group 7 [I1] PAPER 1 Flashcards
trend in electronegativity down group 7 and why?
• decreases down group
• more shells, so more shielding
• weaker attraction between the nucleus and pair of electrons in the covalent bond
trend in atomic radius down group 7 and why?
• increases down group
• more shells
• bigger atom
trend in melting and boiling points down group 7 and why?
• increases
• more electrons
• molecule gets bigger
• more van der Waals’ forces between the molecules
• more energy required to overcome these forces
trend in first ionisation energy down group 7 and why?
• decreases down group
• more shells, so more shielding
• weaker attraction between nucleus and outer electron
trend in oxidising power down group 7 and why?
• decreases down group
• atomic radius increases, so gets larger
• more shielding
• weaker forces of attraction between nucleus and electron to be gained
what does the relative oxidising strengths of the halogens give them the ability to do?
• displace one another
• Cl2 will displace both Br- and I- ions
• Br2 will displace I- ions
• I2 won’t displace any halide ions
• what happens to each thing can be written as half equations
what is oxidising power?
ability to gain an electron
trend in reducing ability of halide ions and why?
• increases down group
• more shielding
• atomic radius increases
• weaker attraction between outer electron that is lost and the nucleus
equation, reaction type and observations for the reaction between solid NaF / NaCl and conc. sulfuric acid?
• NaF + H2SO4 → NaHSO4 + HF
• NaCl + H2SO4 → NaHSO4 + HCl
• steamy fumes
•reaction type - acid-base
equations, reaction types and observations for the reaction between solid NaBr and conc. sulfuric acid?
equations, reaction types and observations for the reaction between solid NaI and conc. sulfuric acid?
ability of halide ions to reduce sulfuric acid?
how to test for halide ions?
• add silver nitrate solution that has been acidified by dilute nitric acid (acidified to remove ions that may interfere with results, so result in false positive results)
• chloride ions produce a white precipitate (AgCl)
• bromine ions produce a cream precipitate (AgBr)
• iodide ions produce a yellow precipitate (AgI)
to distinguish between the precipitates:
• AgCl dissolves in dilute ammonia
• AgBr dissolves in conc. ammonia
• AgI doesn’t dissolve any ammonia solution
equation for the reaction of chlorine with water?
Cl2 + H2O ⇌ HCl + HClO
equation for the reaction of chlorine with water, in the presence of UV light?
2Cl2 + 2H2O ⇌ 4HCl + O2
equation for the reaction between cold, aqueous NaOH and chlorine, and use of the product formed?
sodium chlorate (I) solution is an ingredient of bleach and used to disinfect
Chlorine is used to treat water, despite being toxic to humans. Why is water treated with chlorine, and why is it used, despite the toxicity?
• sterilises water
• health benefit outweighs the risk and it is only used in small quantities/low concentrations
What is observed when silver nitrate solution is added to sodium fluoride solution?
Colourless solution
What is the role of (1) halide ions and (2) sulfuric acid when reacting with conc. sulfuric acid to form NaH2SO4 and HX [X = halogen]?
(1) base / proton acceptor
(2) proton donor
Halide ions reactions and observations (no organic solvent)
Halide ions reactions and observations (with organic solvent)
Explain why some of the reactions that occur when sodium bromide/iodide react with conc. sulfuric acid are redox reactions.
• Br/I changes oxidation state from -1 to 0 and is oxidised
• S changes oxidation state from +6 to +4/0/-2 and is reduced
Explain why bromide ions react differently from chloride ions
• Bromide ions are bigger than chloride ions
• So, bromide ions are more easily oxidised
A colourless solution contains a mixture of sodium bromide and sodium chloride.
Using aqueous silver nitrate and any other reagents of your choice, develop a procedure to prepare a pure sample of silver bromide from this mixture.
Explain each step in the procedure and illustrate explanations with equations, where appropriate.
• Add silver nitrate to form precipitates of AgCl and AgBr:
– AgNO3 + NaCl → AgCl + NaNO3
– AgNO3 + NaBr → AgBr + NaNO3
• Add an excess of dilute ammonia to the mixture of precipitates to dissolve the AgCl precipitate:
– AgCl + 2NH3 → Ag(NH3)2+ + Cl-
• Filter off the remaining silver bromide precipitate
• Wash to remove soluble compounds
• Dry to remove water
A solution of sodium chlorate(l) was added to a colourless solution of potassium iodide.
Suggest what is observed.
Explain the reaction that leads to this observation.
Goes brown due to iodine, because iodide ions are oxidised.
State which gas produced in the reaction between solid NaI and conc. H2SO4 smells gross
hydrogen sulfide (H2S)
Equation for the addition of ammonia to AgX precipitate when testing for halide ions with silver nitrate solution and ammonia?
[X = halogen]
AgX + 2NH3 → Ag(NH3)2+ + X-
Suggest a disadvantage of treating water with chlorine.
• Wasteful as most potable water isn’t used for drinking
• Some people suffer eye irritation
• Some people find the taste unpleasant
• Can react with organic compounds to produce harmful substances
