Inorganic 3: Group 7 Flashcards
Describe the physical properties of the halogens at room temperature.
Fluorine = pale yellow gas
Chlorine = green gas
Bromine = red/brown liquid
Iodine = black solid
Why is the F-F bond so weak?
Fluorine atoms are very small
So the non-bonding electrons repel as they are so close together
Which weakens the bond
What is electronegativity?
The power of an atom to attract the bonding pair of electrons in a covalent bond
How do melting and boiling points change down group 7?
1) Melting and boiling points increase
2) Larger atoms have more electrons so van der Waal forces increase
Which group 7 elements are the best oxidising agents?
1) Fluorine is the best oxidising agent
2) Because it is the most electronegative so attracts electrons more strongly
3) Oxidising ability decreases down the group
How do halogens react with metal halides?
The halide in the compound will be displaced by a more reactive halogen
How does reactivity change down group 7?
Fluorine is the most reactive
Iodine is the least reactive
How would chloride ions react with chlorine, bromine, and iodine?
Chloride ions would not be displaced by any halogen
How would bromide ions react with chlorine, bromine, and iodine?
Bromide ions would be displaced by chlorine
A yellow solution of aqueous bromine would form
Cl2 + 2Br- –> 2Cl- + Br2
How would iodide ions react with chlorine, bromine, and iodine?
Iodide ions would be displaced by chlorine
A brown solution would form
Cl2 + 2I- –> I2 + 2Cl-
Iodide ions would be displaced by bromine
A brown solution would form
Br2 + 2I- –> 2Br- + I2
Explain displacement reactions between metal halides and halogens.
Halogen atoms gain an electron when it oxidises the halide ion
The smaller the halogen, the easier it is to gain an electron
As there is less shielding
So a stronger force of attraction from the nucleus
Which halide ions are the best reducing agents?
Strongest reducing agent = iodide
Weakest reducing agent = fluoride
Why Is iodide the strongest reducing agent?
Iodide has the largest ionic radius, so the outer electron is further form the nucleus
So the attraction between the nucleus and outer electron is weaker
Describe a reaction of chloride ions with concentrated sulfuric acid.
H+ + Cl- –> HCl
Observation: White fumes
Type of reaction: Acid-base
Describe a reaction of bromide ions with concentrated sulfuric acid.
1) Acid-base
H+ + Br- -> HBR
Observation: White fumes
2) Redox
H2SO4 + 2H+ + 2Br- –> Br2 + SO2 + 2H2O
Observation: Orange/brown fumes (Br2) and colourless gas (SO2)
Describe a reaction of iodide ions with concentrated sulfuric acid.
1) Acid base
H+ + I- –> HI
Observation: Steamy fumes
2) Redox
H2SO4 + 2H+ + 2I- –> I2 + SO2 + 2H2O
H2SO4 + 6H+ + 6I- –> 3I2 + S + 4H2O
H2SO4 + 8H+ + 8I- –> 4I2 + H2S + 4H2O
Observations:
Black solid (I2)
Colourless gas (SO2)
Yellow solid (S)
Colourless gas (H2S)
Why doesn’t silver fluoride form a precipitate?
Because it is soluble in water
Describe how you would test for metal halides.
1) Add dilute nitric acid to remove any carbonate or hydroxide impurities which would interfere with the test
2) Add silver nitrate (AgNO3) to form the silver halide precipitates
Silver chloride = white precipitate
Silver bromide = cream precipitate
Silver iodide = pale yellow precipitate
3) Further test: silver chloride dissolves in dilute ammonia, silver bromide dissolves in concentrated ammonia, silver iodide is insoluble in concentrated ammonia
Describe how chlorine reacts with water (not in sunlight).
In a reversible reaction:
Cl2(g) + H2O(l) —> HClO (aq) + HCl (aq)
This is a disproportionation reaction as some atoms of the same element are oxidised while others are reduced
What is HClO?
Chloric(I) Acid
Used as an oxidising agent to kill bacteria
Also a bleach
What is chlorine used for?
Purifying water for drinking
In swimming baths
Give an equation for how chlorine reacts with water in sunlight.
2Cl2(g) + 2H2O (l) —> 4HCl(aq) + O2(g)
What is an alternative to direct chlorination of pools? (give an equation)
Add sodium chlorate (I) which dissolves in water to form chloric(I) acid (HClO) in a reversible reaction:
NaClO(s) + H2O(l) –> Na+ (aq) + OH-(aq) + HClO(aq)
Why are swimming pools always kept slightly acidic?
Because in alkaline solution, the equilibrium of this reaction:
NaClO(s) + H2O(l) –> Na+ (aq) + OH-(aq) + HClO(aq)
Moves slightly to the left, so HClO is removed as ClO- ions (harmful to health)
