Group 7 Halogens and REDOX Flashcards
Oxidising agent
Electron acceptor
Reducing agent
Electron donor
State the equation for the reaction between chlorine and cold water and explain what type of reaction it is
Cl2 + H2O -> HClO + HCl Disproportionation reaction (Cl is oxidised and reduced)
Describe displacement reactions between halogens and halide ions
Reactivity decreases down Group 7 Cl2 displaces Br- - orange-brown solution Cl2 displaces I- - brown solution-black solid Br2 displaces I- - dark brown solution-black solid (NEVER GREY SOLUTION)
sodium halide reacts with element in test (NOT ion with NaX)
Name products iodide ions can reduce sulphuric acid into (give oxidation state of sulphur in each) and suggest observations
SO2 (+4) - pungent / choking gas
S (0) - yellow solid
H2S (-2) - smell of bad eggs
Suggest why pool water can become more acidic than usual on a hot day and give an equation to support your reason
Pool water contains chlorine which reacts with water to produce HClO (chloric I acid) - disinfectant that kills bacteria
In the presence of sunlight chloric I acid decomposes to form even more HCl
2Cl2 + 2H2O -> 4HCl + O2
Give an example of a reagent that can be used to show that the reducing ability of bromide ions is different to chloride ions
CONCENTRATED H2SO4
Give equations for the reactions between chlorine and cold sodium hydroxide and suggest uses of the resulting solution
Cl2 + 2NaOH -> NaCl + NaClO + H2O
NOT Cl2 + NaOH -> NaClO + HCl since hydrochloric acid is neutralised by NaOH
NaClO = bleach/disinfectant
Suggest why fluoride ions cannot be tested for using silver nitrate
Silver fluoride is soluble so no precipitate
Test for halides using concentrated sulphuric acid
F-/Cl- steamy acidic fumes (of HF/HCl)
Br- steamy acidic fumes (of HBr) and brown vapour (Br2)
I- steamy acidic fumes (of HI) and purple vapour (I2)
Identify additional gaseous products formed when potassium bromide/iodide react with concentrated sulphuric acid and state the type of reaction
HBr and HI in acid-base reaction
Explain the colour changes observed when universal indicator paper is dipped into chlorine water
Turns red due to H+ ions from HCl then white since it is bleached by HClO
Give equation for reaction between chlorine and hydroxide ions
Cl2 + 2OH- -> ClO- + Cl- + H2O
- write out ionic equation
- replace H+ with OH- on both sides
- cancel out excess water on both sides
Evaluate the use of chlorine in water treatment
- kills bacteria
- toxic in high quantities
- eye irritation
- may react with organic compounds to make harmful substances
Test for solid metal halides
nitric acid/ silver nitrate solution
Cl- - white precipitate
Br- - cream precipitate
I- - yellow precipitate
Suggest why nitric acid is added when testing for metal halides
Removes carbonate and hydroxide impurities which could react with silver
Suggest why you cannot investigate fluorine in displacement reactions
Fluorine in aqueous solution reacts with water
How to write half equations in alkaline conditions
- first balance in acidic conditions
- for each H+ add one OH- to both sides
- cancel H20
Describe reaction between sodium chloride and concentrated sulphuric acid
NaCl + H2SO4 -> HCl + NaHSO4
(not -> Na2SO4 + 2HCl since requires stronger base)
- steamy acidic fumes of HCl which turn blue litmus paper red
Describe reaction between bromide ions and concentrated sulphuric acid
2Br- -> Br2 + 2e- H2SO4 + 2H+ + 2e- -> SO2 + 2H2O 2Br- + H2SO4 + 2H+ -> Br2 + SO2 + 2H2O - steamy acidic fumes of HBr - brown vapour - pungent gas
Describe reaction between iodide ions and concentrated sulphuric acid
2I- -> I2 + 2e- H2SO4 + 8H+ + 8e- -> H2S + 4H2O 8I- + H2SO4 + 8H+ -> 4I2 + H2S + 4H2O - steamy acidic fumes of HI - purple vapour / dark grey solid - rotten egg smell
What is the oxidation state of O in H2O2
-1
Give equation for reaction between NaBr and concentrated sulphuric acid
2NaBr + 3H2SO4 -> 2NaHSO4 + Br2 + 2H2O + SO2
memorise products and balance NaHSO4 formed for NaI as well
