3.2.3 Group 7 Knowledge Flashcards
explain the trend in atomic radius down group 7
- atomic radius increases down the group
- increased number of electron shells
- electrons repel each other
explain the trend in oxidising ability down group 7
- oxidising ability decreases down the group
- larger atomic radius and increased shielding (offsetting the effect of the greater nuclear charge)
- weaker attraction between nucleus and incoming electron
describe what occurs in a halogen displacement reaction
a halogen higher in the group can oxidise the ions of one lower down and displace it from its compound
what element is an exception from halogen displacement reactions?
Fluorine
why is fluorine an exception from halogen displacement reactions?
- it is too strong an oxidising agent
- Fluorine oxidises water to oxygen and so it is impossible to do simple solution reactions with it.
explain the trend in reducing ability down group 7
- reducing strength increases down group
- ionic radius increases
- there is a weaker attraction between the outermost electron and nucleus
what is this type of reaction: Fluorine + Sulfuric acid
acid-base reaction
why does fluorine undergo an acid-base reaction with sulfuric acid?
fluorine is too weak as a reducing agent to reduce sulfuric acid, so it undergoes an acid-base reaction instead
what is the word equation for the reaction between fluorine and sulfuric acid?
Sodium Fluoride + Sulfuric acid ⇒ Sodium Bisulphate + Hydrogen Fluoride
what is the symbol equation for the reaction between fluorine and sulfuric acid?
NaCl + H₂SO₄ ⇒ NaHSO₄ + HF
what is the half equation for the reaction between fluorine and sulfuric acid?
H⁺ + F⁻ ⇒ HF
what is the observation for the reaction between fluorine and sulfuric acid?
misty/steamy fumes of hydrogen fluoride
what is this type of reaction: chlorine + Sulfuric acid
acid-base reaction
why does chlorine undergo an acid-base reaction with sulfuric acid?
chlorine is too weak as a reducing agent to reduce sulfuric acid, so it undergoes an acid-base reaction instead
what is the word equation for the reaction between chlorine and sulfuric acid?
Sodium Chloride + Sulfuric acid ⇒ Sodium Bisulphate + Hydrogen Chloride
what is the symbol equation for the reaction between chlorine and sulfuric acid?
NaCl + H₂SO₄ ⇒ NaHSO₄ + HCl
what is the half equation for the reaction between chlorine and sulfuric acid?
H⁺ + Cl⁻ ⇒ HCl
what is the observation for the reaction between chlorine and sulfuric acid?
misty/steamy fumes of hydrogen chloride gas
what type of reaction occurs between bromine and sulfuric acid?
acid-base or redox
what is the word equation for the acid-base reaction between bromine and sulfuric acid?
Sodium Bromide + Sulfuric Acid ⇒ Sodium Bisulphate + Hydrogen Bromide
what is the word equation for the redox reaction between bromine and sulfuric acid?
Sodium Bromide + Sulfuric Acid ⇒ Sulfur Dioxide + Water + Bromine
what is the symbol equation for the acid-base reaction between bromine and sulfuric acid?
NaBr + H₂SO₄ ⇒ NaHSO₄ + HBr
what is the ionic symbol equation for the redox reaction between bromine and sulfuric acid?
H2SO4 + 2H+ + 2Br- ⇒ Br2 + SO2 + 2H2O
what is the half equation for the acid-base reaction between bromine and sulfuric acid?
H⁺ + Br⁻ ⇒ HBr
what are the half equations for the redox reaction between bromine and sulfuric acid?
- 2Br⁻ ⇒ Br₂ + 2e⁻
- 2e⁻ + 2H⁺ + H₂SO₄ ⇒ SO₂ + 2H₂O
what is the observation for the acid-base reaction between bromine and sulfuric acid?
misty/steamy fumes of hydrogen bromide
what is the observation for the redox reaction between bromine and sulfuric acid?
brown fumes and acidic/toxic gas
what type of reaction occurs between iodine and sulfuric acid?
acid-base or redox
what is the word equation for the acid-base reaction between iodine and sulfuric acid?
Sodium Iodide + Sulfuric Acid ⇒ Sodium Bisulphate + Hydrogen Iodide
what is the symbol equation for the acid-base reaction between iodine and sulfuric acid?
NaI + H₂SO₄ ⇒ NaHSO₄ + HI
what is the half equation for the acid-base reaction between iodine and sulfuric acid?
H⁺ + I⁻ ⇒ HI
what is the observation for the acid-base reaction between iodine and sulfuric acid?
misty/steamy fumes of hydrogen iodide
what is the word equation for the first redox reaction between iodine and sulfuric acid?
Sodium Iodide + Sulfuric Acid ⇒ Sulfur Dioxide + Water + Iodine
what is the word equation for the second redox reaction between iodine and sulfuric acid?
Sodium Iodide + Sulfuric Acid ⇒ Sulfur + Water + Iodine
what is the word equation for the third redox reaction between iodine and sulfuric acid?
Sodium Iodide + Sulfuric Acid ⇒ Hydrogen Sulfide + Water + Iodine
what is the ionic symbol equation for the first redox reaction between iodine and sulfuric acid?
2H+ + 2I- + H2SO4 ⇒ SO2 + 2H2O + I2
what is the symbol equation for the second redox reaction between iodine and sulfuric acid?
6H+ + 6I- + H2SO4 ⇒ S + 4H2O + 3I2
what is the symbol equation for the third redox reaction between iodine and sulfuric acid?
8H+ + 8I- + H2SO4 ⇒ H2S + 4H2O + 4I2
what are the half equations for the first redox reaction between iodine and sulfuric acid?
- 2I⁻ ⇒ I₂ + 2e⁻
- 2e⁻ + 2H⁺ + H₂SO₄ ⇒ SO₂ + 2H₂O
what are the half equations for the second redox reaction between iodine and sulfuric acid?
- (2I⁻ ⇒ I₂ + 2e⁻) x3
- 6e⁻ + 6H⁺ + H₂SO₄ ⇒ S + 4H₂O
what are the half equations for the third redox reaction between iodine and sulfuric acid?
- (2I⁻ ⇒ I₂ + 2e⁻) x4
- 8e⁻ + 8H⁺ + H₂SO₄ ⇒ H₂S + 4H₂O
what are the observations for the third redox reaction between iodine and sulfuric acid?
forming hydrogen sulfide: black solid, bad egg smell
what are the observations for the second redox reaction between iodine and sulfuric acid?
forming sulfur: black and yellow solids
what are the observations for the first redox reaction between iodine and sulfuric acid?
forming sulfur dioxide: black solid, acidic gas
describe the process of the halide test
- dissolve sample in water (if not already an aqueous solution)
- Add HNO₃
- Add AgNO₃ (aq) solution
- Add dilute NH₃ to the sample
- Add concentrated NH₃ to the sample
why is HNO₃ added before AgNO₃ in the halide test?
used to remove any possible CO₃²⁻ impurities which would give a false positive
what acids should not be used before AgNO₃ in the halide test? and why?
HCl (as it contains a halide) or H₂SO₄ (it will undergo redox or acid-base reactions)
what is a positive result for fluoride in the halide test?
no ppt
what is a positive result for chloride in the halide test?
white ppt which dissolves in dilute ammonia solution
what is a positive result for bromide in the halide test?
cream ppt which dissolves in concentrated ammonia solution
what is a positive result for iodide in the halide test?
yellow ppt which does not dissolve in any ammonia solution
what is the fluoride precipitate formed in the halide test?
Ag⁺ (aq) + F⁻ (aq) ⇒ AgF (aq)
what is the chloride precipitate formed in the halide test?
Ag⁺ (aq) + Cl⁻ (aq) ⇒ AgCl (s) [white]
what is the bromide precipitate formed in the halide test?
Ag⁺ (aq) + Br⁻ (aq) ⇒ AgBr (s) [cream]
what is the iodide precipitate formed in the halide test?
Ag⁺ (aq) + I⁻ (aq) ⇒ AgI (s) [yellow]
give the half equation for the reaction between ammonia and a silver halide ppt in the halide test
Ag⁺ (aq) + 2NH₃ (aq) ⇐⇒ [Ag(NH₃)₂]⁺ (aq)
why is chlorine added to water?
it sterilises it by killing bacteria
why must the chlorine added to water be a low concentration?
chlorine is toxic
give the symbol equation for the reaction between chlorine and water
Cl₂ + H₂O ⇄ HCl + HClO
what type of reaction is the reaction between chlorine and water
disproportionation [Cl₂ is reduced to HCl (oxidation state change: 0 to -1)
Cl₂ is oxidised to HClO (hypochlorous acid) (oxidation state change: 0 to +1)]
