Inorganic- The Halogens

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  • Created by: Hindleyc
  • Created on: 16-06-18 16:55
What happens to the melting and boiling point as you go down the group? why?
Increase as molecules become larger they have more electrons and larger V.D.W between molecules so as the intermolecular forces get larger more energy has to be put in to break the forces increasing mp and bp
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What is electronegativity?
Relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself
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What happens to electronegativity as you go down the group?why?
decreases because AR increases due to inc number of shells so nucleus less able to attract bonding pair of electrons
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What will a Halogen that is a strong oxidising agent do?
Displace a halogen that has a lower oxidising power from one of its compounds
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What happens to oxidising strength as you go down the group?
decreases
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What are oxidising agents?
Electron acceptors
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What will Chlorine displace? what will Bromine displace?
Both bromine and and iodine ions. Iodine
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What shows which free halogen is present in solution?
Colour of solution
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What is Chlorines colour?
V. Pale green solution often colourless
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What is Bromine
Yellow solution
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Whats Iodine?
Brown solution sometimes black solid present
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What is the reaction of halide ions with silver nitrate used to test for?
Which halide ion is present
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What happens to the test solution?
Made more acidic with nitric acid then silver nitrate solution added dropwise
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What is the the role of nitric acid?
React with any carbonates present to prevent formation of precipitate AgCO3 as would mask desired observations
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eqn?
2HNO3+Na2CO3=2NaNO3+H2O+CO2
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Fluorine observation?
No precipitate
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Chlorine observation
White precipitate- Ag+(aq)+Cl-(aq)= AgCl(s)
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Bromine observation?
Cream precipitate- Ag+(aq)+Br-(aq)=AgBr(s)
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Iodine observation
Pale Yellow precipitate Ag+(aq)+I-(aq)=AgI(s)
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What can the silver halide precipitates be treated with to help differentiate between them if the colours look similar?
Ammonia solution
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What do Silver Chloride do?
Dissolves in DILUTE ammonia to form a complex ion- AgCl(s)+2NH3(aq)=[Ag(NH3)2]+(aq)+Cl-(aq) colourless solution
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What does silver bromide do?
Dissolves in CONCENTRATED ammonia to form complex ion- AgBr(s)+2NH3(aq)=[Ag(NH3)2]+(aq)+Br-(aq) Colourless solution
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What does silver iodide do?
Does not react with ammonia- it is too insoluble
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What is F2 like?
V Pale yellow gas- highly reactive
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Cl2?
Greenish reactive gas- poisonous in high conc
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Br2?
Red liquid- gives off dense brown/orange poisonous fumes
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I2?
Shiny grey solid sublimes to purple gas
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What do halides show increasing power as going down the group?
Reducing agents
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What is a reducing agent?
Donates electrons
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Why does reducing power increase?
Have greater tendency to donate electrons because ions get bigger and it is easier for the outer electrons to be given away as the pull from the nucleus on them become smaller
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Reaction of Chlorine and Fluorine with Concentrated sulfuric acid?
F- and Cl- aren't strong enough reducing agents to reduce S in the H2SO4 so no redox reaction occurs only acid base reactions occur
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eqn for NaF(s) and sulfuric acid? observations?
NaF(s)+H2SO4(l)= NaHSO4(s)+HF(g). White steamy fumes of HF evolved
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eqn for NaCl(s) and sulfuric acid? observations?
NaCl(s)+H2SO4(l)=NaHSO4(s)+HCl(g). White steamy fumes of HCl evolved
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What does H2SO4 play the role of?
An Acid- proton donor
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Bromine ions?
Stronger reducing agents than Cl- and F- and after initial acid-base reaction reduce the sulfur in h2so4 from +6 to +4 in SO2
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Acid base step:
NaBr(s)+H2SO4(l)=NaHSO4(s)+HBr
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Redox step:
2HBr+H2SO4=Br2(g)+SO2(g)+2H2O(l)
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What does the H2SO4 play the role of?
An acid in first step producing Her and then acts as oxidising agent in second redox step
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Observation
White steamy fumes of HBr evolved. Red fumes of Br also evolved and colourless acidic gas- SO2
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Reduction product?
Sulfur dioxide
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Iodine ions?
Strongest halide reducing agents- can reduce sulphur from +6 in h2so4 to +4 in so2 to 0 in S and -2 in H2S
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First eqn
NaI(s)+H2SO4(l)=NaHSO4(s)+HI(g)
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2nd
2HI+H2SO4=I2(s)+SO2(g)+2H2O(l)
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3rd?
6HI+H2SO4=3I2+S(s)+4H2O(l)
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4th
8HI+H2SO4=4I2(s)+H2S(g)+4H2O(l)
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Observation?
White steamy fumes of HI evolved. black solid and purple fumes of iodine are evolved. Colourless acidic gas so2. yellow solid of sulphur. H2S (hydrogen sulphide) a gas with bad egg smell
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Reduction products?
Sulfur dioxide, sulphur and hydrogen sulphide
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H2SO4?
Role of acid in first step to make HI and oxidising agent in 3 redox steps
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