Topic 12-Introduction to redox and group 7 Flashcards
Rules for oxidation states
In a monatomic atom- its the given charge
Oxygen nearly always -2 except for peroxides where its -1
Hydrogen is nearly always +1 except for hydrides where its -1
Elements always 0
Trends in halogens
Boiling point increases down the group- due to increased mass of molecules
Electronegativity decreases down the group- Increased atomic radius and sheilding
Halogens displace less reactive halides
Trends in halogens
Boiling point increases down the group- due to increased mass of molecules
Electronegativity decreases down the group- Increased atomic radius and sheilding
Halogens displace less reactive halides
Reaction of halogens with potassiumhalide solutions
Chlorine- Will displace bromide and iodide- forming an orange and brown solution respectively
Bromine- Will Displace iodide- forming brown solution only
Iodine will not displace anthing
Reaction of chlorine with sodium hydroxide
2NaOH + Cl2 –> NaClO(bleach) + NaCl + H2O
Uses of sodium chlorate
- Water treatment
- Bleaching paper and textiles
- Cleaning toilets
Reaction of chlorine in water (Type and equation)
Disproportionation
Cl2 + H2O <—–> HCl + HClO
Positives of use of chlorine in water
- Kills disease
- Remains in water, preventing reinfection
- Prevents growth of algae
- Removes discolouration caused by organic products
Negatives of chlorine treatment
- Chlorine is very harmful- accidents with it could be fatal
- Chlorine can react with hydrocarbons- forming chlorinated hydrocarbons which are carcinogenic
Why does the strength of reducing agent increase down a group
- Ions get bigger- electrons are further away from the positive nucleus
- There are extra inner electron shells, so greater sheilding effect
Main products in reaction with sulfuric acid (Each halogen)
Fluorine and Chlorine- HF + HCL
Bromine- HBr + SO2
Iodine- HI + SO2 + H2S
Why do reducing agents get better as you go down group 7?
Larger atomic radius
More sheilding
Easier to lose an electron
Why do oxidising agents get better up a group?
Lower atomic radius
Less sheilding
Charge from nucleus is felt more
Testing for halides
- Add dilute nitric acid and silver nitrate
- (F- No precipitate) (Cl- White) (Br- Cream) (I- yellow)
Solubility of silver halides in ammonia
Chloride- Dissolves in dilute
Bromide- Dissolves in conc NH3
Iodide- Insoluble even in conc NH3