2.3 Group 7, the halogens Flashcards
What are the colours and standard states of the 4 main halogens?
Fluorine - pale yellow gas
Chlroine - green gas
Bromine - red-brown liquid
Iodine - black solid
Why does fluorine have unexpectally weak diatomic molecules?
The F atoms are very small meaning the repulsive, non bonding pairs are close together
What is the general trend for electronegativity down group 7?
Electronegativity decreases down the group with fluorine anomolously high
What is the general trend for melting and boiling points down group 7?
They increase down the group as the VdW forces increase the more electrons there is
What is the general trend for oxidising power down group 7?
Oxidising power decreases going down the group as the nucleus is further away from the outer energy levels meaning it is harder to gain electrons
What is the general trend for displacement reactions of halogens and metal halides?
The elements higher in the group will displace the elements lower down from the metal.
What part of a displacement reaction causes the colour of the solution?
The dissolved diatomic molecule, e.g Br2 will cause a red-brown colour
What will the equation and colour change be where sodium iodide reacts with bromine?
Br2 + 2NaI → I2 + 2NaBr
Brown-red solution to black solution
Write the ionic equation and describe any observations between sodium bromide and chlorine
Cl2 + 2Br- → Br2 + 2Cl-
Colourless solution to red-brown solution
What is the general trend for halogens as reducing agents?
The further down the group you go, the easier it is for the halogen to lose an electron
What reaction happens when solid sodium chloride reacts with concentrated sulphuric acid and why?
NaHSO4(s) and HCl(g) are formed as the chlorine is too weak of a reducing agent to lower the sulphurs +6 oxidation state. The HCl will appear as a colourless gas coming from the reaction.
What reactions happens when solid sodium bromide reacts with concentrated sulphuric acid and why?
NaBr + H2SO4(l) → NaHSO4(s) and HBr(g)
2H+ + 2Br- + H2SO4(l) → SO2 + 2H2O + Br2
The bromine is a strong enough oxidising agent to reduce the sulphur to sulphur dioxide changing its oxidation state from +6 to +4
What are the products of the reaction of solid sodium iodide and concentrated sulphuric acid and why?
- NaHSO4(s) and HI(g)
- SO2 + 2H2O + I2
- S + 4H2O + 3I2
- H2S + 4H2O + 4I2
The iodine is a strong enough reducing agent to reduce sulphurs oxidation state from +6 to +4, 0 and -2
How can you indentify the sulphur products of the reaction between metal halides and concentrated sulphuric acid?
SO2 - colourless gas
H2S - strong, bad egg smell
S - yellow solid
Describe the test for halide ions by their precipates and the results for fluorine, chlorine, bromine and iodine
- Add HCl to remove carbonate ions
- Add silver nitrate solution to the solution you’re testing
Fluorine→No precipitate
Chlorine→White precipitate→Redissolves in dilute ammonia solution
Bromine→Cream precipitate→Redissolves in concentrated ammonia
Iodine→Yellow precipitate→Doesn’t redissolve
What are the products from the reaction of chlorine and water and what is chlorines oxidation state in each?
Chloric acid, HClO (Cl +1), and hydrochloric acid, HCl (Cl -1)
How is chlorine used to keep swimming pools clean and why do pools in direct sunlight need additonal chlorine?
Chloric acid kill bacteria but in direct sunlight the reaction between water and chlorine can form double the about of HCl and oxygen.
What are the products and uses of the reaction between chlorine and cold, dilute sodium hydroxide?
NaClO, an active ingredient in bleach, NaCl and H2O
