Group 7: Halogens
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Sorted FAQs on Group 7: Halogens
This topic has attracted quite a lot of questions to Re:act over the years. To help you find the ones of most interest to you more easily, whether they are about background theory or a particular experiment, we have sorted the FAQs under several headings below, with a direct link to each question and answer.
1. Properties and Uses
•Oxidation state of Br in naturally occurring compounds?
•Why is iodine coloured?
•Colours of halogens in hydrocarbon solvents?
•Colour of halogens in water and hydrocarbons, and reasons?
•Purple molecular crystal that sublimes?
•Uses of the halogens?
•Bromine: use as bromine water vs pure liquid
•Colour of KBr?
•Chlorine as antibacterial
•Purification of bromine
•Toxic properties of chlorine
2. Solubility and reactions with water
•Solubility of iodine: why in hydroarbons but not in water?
•Relative solubility of halogens in water and propanone
•Why halogens more soluble in hydrocarbon solvent than water?
•Reactions chlorine, bromine and iodine with water?
•Value for distribution coefficient for I2 in hexane <=> I2 in KI(aq)?
•I2 distribution equilbrium: effect of I2 concentration on Kd?
•Partition coefficient of iodine: why KI added to water layer?
3. Extraction
•Extraction of iodine: reaction acidified hydrogen peroxide?
•Extraction of iodine: use of solvents
•Iodine: extraction from a hydrocarbon solvent?
•Iodine extraction: isolating iodine from solution in a hydrocarbon solvent?
•Why does iodine occur in seaweed? Role?
4. Tests for halides in solution
•Halides + silver nitrate: equations for reactions?
•Tests for halide ions in solution?
•Test for fluoride ion using silver nitrate?
•Reactions of halide ions: observations?
•AgNO3 + NaCl: equation. observation and interpretation?
•Reaction of halides with silver nitrate
5. Redox reactions
•What is a disproportionation reaction?
•Many oxidation numbers for Cl, F only 1: why?
•Reaction between iodine, red P and ethanol?
•Reaction chlorate(I) and chlorate(V) with Fe2+ and with iodide ions?
•Chlorine + KI solution: colour change?
•Reaction of halogens with halides in solution: observations?
•Equation for reaction between SO2 and iodine?
•Products of the reaction between iodine and sulphur dioxide?
•Oxygen formed from chlorate(I) + hydrogen peroxide: why?
•Making KIO3: use of solubility graph?
•Preparation of KI and KIO3: explanation?
6. Thiosulphate titrations
•Thiosulphate titration: why are iodide ions colourless and the starch/iodine complex black?
•Standardising thiosulphate solution: use of iodate, acid and iodide?
•Standardisation of iodine solution: why and how?
•Iodine determination: titration vs colorimetry?
•Stability of iodine-starch colour
•Iodine in hydrocarbon solution: why does colour fade?
•Cu determination by iodine titration: method?
•% Purity of KIO3 titration: state symbols for equations?
•Iodate titration with thiosulphate: end-point errors?
7. Period 3 chlorides
•Reaction of period 3 chlorides with water?
•Reactions chlorine with Period 3 elements
•Why is SiCl4 attacked by water but CCl4 not?
8. Preparation and properties of hydrogen halides
•Halides + conc. sulphuric acid: reasons for differences?
•Making HI: sulphuric vs phosphoric acid
•Reaction between KI and conc. H2SO4: balanced equation?
•Half equations for reaction of conc. H2SO4 with bromide ions?
•Reaction of K-halides with conc. phosphoric acid: products?
•Reaction of halides with conc. sulphuric acid: products formed?
9. Determination of chlorine
•Chloride determination by silver nitrate titration: how does it work?
•Chlorine content of bleach: method using iodide and thiosulphate?
•Determination of Cl2: back titration using Fe2+salt - which suitable?
•Determination of Cl2by back titration using Fe2+salt: acid needed?
•Chlorine determination with peroxide: meaning of 'volumes' for peroxide concentration?
•Chlorine in bleach: other possible reactions?
•% Chlorine in bleach by gravimetric analysis
•Bleach - dilution and deterioration
10. Determination of chloride
•Determination of chloride by silver nitrate titration: wrong indicator?
•Salt content of crisps: easiest method?
•Solubilities of metal halides: planning titration with silver nitrate?
•Titration of halides with with silver nitrate: which needs most?
•Titration of chloride with silver nitrate: why pH 6 - 10?
•Determination of salt in crisps: method?
•Halide + silver nitrate: type of reaction?
•Chloride determination - Fajan's method
11. Miscellaneous: organic reactions
•Role of reagent in hydrolysis of halogenoalkane?
•Reaction between bromine and phenol?
•Bromine water test: phenol vs an alkene?
•Why is Br2 an electrophile in reaction with alkenes?
•Ascorbic acid- iodine titration: back titration?
•Iodine/propanone reaction: rate by colorimetry or titration?
12. Miscellaneous: inorganic reactions
•Bromine clock reaction: information on mechanism?
•Do halogens themselves react with ammonia?
•Role of phenol in bromate/bromide rate study
•HF + NaOH: species present at neutral point?
•Analysis of fluoride water
•Ways to analyse fluorine in water.
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updated: 08 August 2008
