3.2.3 Group 7 Knowledge Flashcards by Scarlett Davis

explain the trend in atomic radius down group 7

atomic radius increases down the group
increased number of electron shells
electrons repel each other

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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

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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

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what element is an exception from halogen displacement reactions?

Fluorine

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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.

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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

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what is this type of reaction: Fluorine + Sulfuric acid

acid-base reaction

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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

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what is the word equation for the reaction between fluorine and sulfuric acid?

Sodium Fluoride + Sulfuric acid ⇒ Sodium Bisulphate + Hydrogen Fluoride

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what is the symbol equation for the reaction between fluorine and sulfuric acid?

NaCl + H₂SO₄ ⇒ NaHSO₄ + HF

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what is the half equation for the reaction between fluorine and sulfuric acid?

H⁺ + F⁻ ⇒ HF

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what is the observation for the reaction between fluorine and sulfuric acid?

misty/steamy fumes of hydrogen fluoride

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what is this type of reaction: chlorine + Sulfuric acid

acid-base reaction

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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

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what is the word equation for the reaction between chlorine and sulfuric acid?

Sodium Chloride + Sulfuric acid ⇒ Sodium Bisulphate + Hydrogen Chloride

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what is the symbol equation for the reaction between chlorine and sulfuric acid?

NaCl + H₂SO₄ ⇒ NaHSO₄ + HCl

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what is the half equation for the reaction between chlorine and sulfuric acid?

H⁺ + Cl⁻ ⇒ HCl

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what is the observation for the reaction between chlorine and sulfuric acid?

misty/steamy fumes of hydrogen chloride gas

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what type of reaction occurs between bromine and sulfuric acid?

acid-base or redox

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what is the word equation for the acid-base reaction between bromine and sulfuric acid?

Sodium Bromide + Sulfuric Acid ⇒ Sodium Bisulphate + Hydrogen Bromide

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what is the word equation for the redox reaction between bromine and sulfuric acid?

Sodium Bromide + Sulfuric Acid ⇒ Sulfur Dioxide + Water + Bromine

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what is the symbol equation for the acid-base reaction between bromine and sulfuric acid?

NaBr + H₂SO₄ ⇒ NaHSO₄ + HBr

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what is the ionic symbol equation for the redox reaction between bromine and sulfuric acid?

H2SO4 + 2H+ + 2Br- ⇒ Br2 + SO2 + 2H2O

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what is the half equation for the acid-base reaction between bromine and sulfuric acid?

H⁺ + Br⁻ ⇒ HBr

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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

1. dissolve sample in water (if not already an aqueous solution) 2. Add HNO₃ 3. Add AgNO₃ (aq) solution 4. Add dilute NH₃ to the sample 5. 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)]

what does fluorine look like?

very pale yellow gas

what does chorine look like?

greenish, reactive gas

what does bromine look like?

red lqiuid that gives off dense brown/orange poisonous fumes

what does iodine look like?

shiny grey solid sublimes to purple gas

what colour is chlorine in solution?

very pale green, often colourless

what colour is bromine in solution?

orange solution

what colour is iodine in solution?

brown solution

give the equation for the reaction between chlroine and water in bright sunlight?

2Cl2 + 2H2O -> 4H+ + 4Cl- + O2

what colour will univeral indicator be in a solution of Cl2 and H2O?

it will first turn red due to the acidity of both reaction products (HClO and HCl) and then colourless as the HClO bleaches the colour

what is the observation for a reaction between Cl2/Br2/Is and cold NaOH?

the colour of the halogen solution will fade to colourless

give the equation for the reaction between chlorine and cold sodium hydroxide

Cl2(aq) + 2NaOh(aq) -> NaCl(aq) + NaClO(aq) + H2O(l)

what is a mixture of NaCl and NaClO used for?

bleach - to kill bacteria

what is the name of this substance: NaClO

sodium chlorate (I)

what is the name of this substance: NaClO3

sodium chlorate (V)

what is the name of this substance: K2SO4

potassium sulfate (VI)

what is the name of this substance: K2SO3

potassium sulfate (IV)