Group 7 Flashcards
How are the halogens found in nature?
As ions bonded to group 1 metals
Describe and explain the trend in boiling points down the group
Boiling point increases
More electrons
Stronger London forces
More energy to break
Describe the structure of the halogens when solid and gas
Solid = giant molecular lattice
Gas = diatomic molecules
Describe and explain the trend in reactivity down the halogens
Reactivity decreases
Atomic radius and shielding increases (repulsion)
Harder to attract electron (feels less attraction by nucleus)
Nuclear charge increases but is outweighed
Describe a halogen-halide displacement reaction
A more reactive halogen with displace a less reactive halide from its compound
E.g chlorine displaced iodine from sodium iodide
What is added it a halogen -halide displacement reaction to make the products more visible ?
Cyclohexane
How does cyclohexane make displaced halogens more visible?
Cyclohexane is non-polar
Halogens are non-polar
Dissolves halogens
Describe the layers of a halogen-halide displacement reaction when cyclohexane is added. Explain why
Cyclohexane and dissolves halogen form top layer
Bottom layer is water plus salt
Describe and explain the colours of halogens in cyclohexane
Chlorine = green
Bromine =. Orange-brown
Iodine= violet
State whether the halogen or halide is oxidised or reduced
Halogen = reduced
Halide = oxidised
What colour and state is flourine at RTP
Pale Yellow gas
What is a disproportionation reaction?
Give and example
When the same species is oxidised and reduced
Chlorine + water/ NaOH
What are the products of chlorine and water?
Chloric (1) acid
Hydrochloride acid
How does chloric acid purify water ?
The chlorate (1) ions (ClO-) Kill bacteria
What are the disadvantages of adding chlorine to water ?
Chlorinated hydrocarbons (e.g methane from decaying organic matter) are carcinogenic
Chlorine gas is toxic + respiratory irritant
Ethical dilemma (choice?)
What are the advantages to adding chlorine to water
Kills bacteria, eradicate disease
What are the alternatives to adding chlorine to water and why are these not used?
Ozone: short half life so not permanent disinfectant
UV : water may get contaminate down stream, no way to purify then
What are the products of the reaction between chlorine and sodium hydroxide?
Sodium chlorate, sodium chloride and water
Describe how household bleach is produced
Reacting sodium hydroxide with chlorine to produce sodium chlorate (1)
Chlorate (1) ions
Describe a use for bromine
Photographic film
Describe a use for iodine
Medical tracers and cancer treatment
What is the difference between qualitative and quantitative analysis?
Qualitative = what elements are present
Quantitative = how much of each element is present
State the order qualitative analysis should be carried out on an unknown sample
Carbonate test
Sulphate rest
Halide test (silver nitrate and then ammonia)
Ammonium test
Describe the carbonate test
Add acid to sample
Bubble gas produced through line water (saturated Ca(OH)2 solution)
Will turn cloudy due to calcium carbonate precipitate if CO3(2-) present
What acids can and can’t be used in the carbonate test and why
nitric acid (HNO3)
Not sulphuric acid or hydrochloric acid
Will produce false negetive for sulphate or halide test
Describe and explain the sulphate test
Add barium nitrate (Ba(NO3)2)
Barium sulphate precipitate (white) will form
Only sulphate which is insoluble
Why is barium nitrate used in the sulphate test?
Won’t show a false negetive in next tests
Barium chloride will
Why is the sulphate test carried out after the carbonate test?
Barium carbonate will form a white precipitate so will give false negative
Describe the halide test and the results
Add acidified silver nitrate
Halogen will displace nitrate to form silver halide precipitate
Cl= white Br= cream I= yellow
Describe and explain the results after adding ammonia to silver halides
Cl= clear Br= clear I= Cloudy
AgCl and AgBr= polar
Ammonia = polar (like dissolves like)
AgI non-polar because not big enough difference in electronegativity
Describe the test for ammonium ions
Add warm sodium hydroxide
Test with damp red litmus paper (will go blue if positive)
Why is warm NaOH used in the test for ammonium ions?
Ammonia gas produced when NaOH added but highly soluble
Heating releases NH3 gas
Why must the halide test be carried out after the carbonate and sulphate test?
AgCO3 and AgSO4 will form precipitates (false negatives)
Test for copper ions
Add pottasium iodide
White precipitate and brown solution formed
