Group 7 Flashcards
What kind of chemical are the products of the reactions between group 1 and 2 metals and group 7 elements?
Salts which are usually white solids
What colour is
- fluorine?
- chlorine?
- bromine
- iodine?
- pale yellow
- pale green
- brown/orange
- violet
When doing halogen/halide displacement reactions, how can you allow the colour change to be more easily seen? Why does this work?
By adding an organic solvent like cyclohexane after the reaction and then shake the tube. It works as halogens are more soluble in cyclohexane than in water so the halogen dissolves in the organic upper layer where it’s colour can be more easily seen
What kind of reaction are halogen halide displacement reactions an example of?
redox reactions
Out of chlorine, bromine and iodine, why is chlorine the most reactive?
- it has the smallest atom so the incoming electron gets closer to and is more attracted by the protons in the nucleus
- it has the smallest number of complete inner energy levels of electrons so the incoming electron experiences the least repulsion
What is the equation for chlorine added to water? What kind of reaction is it and why? Why is it useful?
- Cl₂ + H₂O -> HCL + HCLO
- this is a disproportionation reaction because the chlorine’s oxidation number went from 0 to -1 in hydrochloric acid (HCL) and +1 in the chloric(I)acid (HCLO)
- adding chlorine to water disinfects it and kills pathogens responsible for water bourn diseases like cholera
What is the equation for chlorine added to a cold alkali for e.g. aqueous sodium hydroxide? What kind of reaction is it and why? Why is it useful?
- Cl₂ + 2NaOH -> NaCl + NaClO + H₂0
- its a disproportionation reaction as the chlorine goes from 0 to -1 in the NaCl and +1 in the NaClO
- its useful as one of the products is sodium chlorate which is a disinfectant that also has useful bleaching action which is extensively used in industry and is the active ingredient in household bleach
When chlorine is added to a hot alkali like concentrated sodium hydroxide solution, what’s the equation? What kind of reaction is it and why? Why is it useful?
- 3Cl₂ + 6NaOH -> 5NaCl + NaClO₃ + 3H₂O
- its a disproportionation reaction as the chlorine goes from 0 to -1 and to +5 in NaClO₃ at the same time
- the sodium chlorate(V) formed is used again in bleaching but also as a weed killer
What’s the trend in oxidising power as you go down group 7?
Oxidising power decreases so fluorine has the highest oxidising power
What’s the trend in reducing power as you go down group 7?
Reducing power increases so Fluorine has the worst reducing power
What’s the general half equation that represents the reducing action of halide ions?
2X- -> X2 + 2e-
What are the three possible reduction products that are a result of sulfuric acid acting as an oxidising agent and so being reduced?
- sulfur dioxide
- sulfur
- hydrogen sulfide
Run through visual changes in the test of halide ions using silver nitrate
The ions are chloride, bromide and iodide ions
When you add silver nitrate to:
-chloride ions, a white precipitate is formed,
-bromide ions a cream precipitate is formed
-iodide ions a yellow precipitate is formed
Then adding dilute aqueous ammonia to each,
-the chloride ions turn colourless again as they are soluble in dilute aqueous ammonia
-and the bromide ions and iodide ions are insoluble so they stay the same
Then adding concentrated aqueous ammonia,
-the solution become colourless as the bromide ions are soluble in concentrated aqueous ammonia
-the iodide ions stay as the yellow precipitate as they are insoluble
When testing for halide ions using silver nitrate, why is dilute nitric acid added before the experiment?
To make sure that any other anions are removed as they would also form precipitates
Why can testing for halide ions using silver nitrate not be used to detect fluorine ions in aqueous solution?
Because the silver fluoride is soluble so wouldn’t form a precipitate
