3I- Group 7, Halogens Flashcards
What’s the trend in electronegativity down group 7
Decreases
Increase in number of protons but valance electrons become further from the nucleus as the number of energy levels increase, due to increasing shielding also electronegativity decreases
What’s the trend in boiling point going down the group
Increase, larger atoms have more electrons, stronger van der waals between molecules
What’s the trend in oxidising ability (oxidising agent)/displacement down the group
Oxidising ability decreases going down the group, ability to receive an electron decreases as electronegativity decreases down the group
More reactive halogens (top) will displace a less reactive one (bottom) in an aqueous solution
What’s the trend in reducing ability (reducing agent) of a halogen
Reducing ability increases down the group, ability to lose electrons increases as valance electrons receives less attraction to the nucleus
What happens in the reaction of solid sodium halides with sulphuric acid
Not a redox reaction, chloride ion is a weak reducing agent and can’t reduce sulphur
Forms hydrogen chloride gas
What does silver nitrate test for, why and how is it used
Tests for halide ions, silver ions combine with halide ions producing silver halide precipitates in different colours
Add nitric acid to the halide solution, removes carbonate or hydroxide impurities
Add a few drops of silver nitrate, halide precipitate forms
AgF- no precipitate
AgCl- white precipitate
AgBr- cream precipitate
AgI- yellow precipitate
Why is nitric acid used before the silver nitrate test and not hydrochloric or sulphuric acid
Sulphuric acid would produce silver sulphate, white precipitate
Hydrochloric acid would produce silver chloride, chlorine ions, white precipitate
Invalidates the test
What’s the trend in solubility of halides in ammonia and why is it used as well as silver nitrate to test for halides
AgCl- dissolves in dilute ammonia
AgBr- dissolves in conc ammonia
AgI- insoluble in conc ammonia
Silver nitrate produces precipitates similar in colour, cream and white, ammonia confirms observations
Reaction of chlorine and water to form chloride ions and chlorate (I) ions
Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
Reaction of chlorine with water to form chloride ions and oxygen
2Cl2 (g) + 2H2O (l) —> 4HCl (aq) + O2 (g)
In sunlight
How is chlorine used in water treatment
Disproportionation reaction forming chloric acid and hydrochloric acid
Chloric acid is an oxidising agent killing bacteria
Reaction of chlorine with cold, dilute aqueous NaOH and uses of solution produced
Cl2 (g) + 2NaOH (aq) —> NaClO (aq) + NaCl (aq) + H2O (l)
Produces sodium chlorate, an oxidising agent used in bleach
