3.2.3 Group 7

Describe fluorine

pale yellow gas

Describe chlorine

pale green gas

Describe Bromine

dark red liquid

Describe Iodine at room temperature and its other form

shiny black solid

sublimes to purple vapour

State and explain the trend in boiling points as you descend the group 7

Increases

atoms/molecules increase in size

stronger van der Waals forces between the molecules

State and explain the trend in electronegativity as you descend the group 7

decreases

the atoms get bigger going down the group

outer electrons are more shielded from the nucleus so the bonding electrons are less electrostatically attracted to the nucleus

State and explain the trend in oxidising ability of the halogens as you descend the group

decreases

atoms get bigger

outermost electron is further from the nucleus so is increasingly shielded

weaker EFA so harder to accept electron

What are oxidant agents in terms of electrons?

electron acceptor

Describe the observations of the reaction of chlorine with Br- ions

colourless solution to orange solution

Describe the observations of the reaction of chlorine with I- ions

colourless solution to brown solution

Describe the observations of the reaction of Bromine with Cl- ions

no visible reaction

Describe the observations of the reaction of bromine with I- ions

colourless solution to brown soluition

Describe the observations of the reaction of Iodine with Br- ions

no visible reaction

Describe the observations of the reaction of Iodine with Cl- ions

no visible reaction

What are all group 1 and 2 compounds?

colourless solutions

What are all group 2 metal compounds at room temp?

White solids

Give the symbol and ionic equation for chlorine and potassium bromide stating what is oxidised and reduced

Symbol: Cl₂ + 2KBr → 2KCl + Br₂

2Br^-—> Br₂ + 2e^- = oxidised
Cl₂ + 2e^- → 2Cl^- = reduced

Ionic: Cl₂ (aq) + 2Br^-(aq) → Br₂ (aq)+ 2Cl^-(aq)

What is a reducing agent?

electron donor

Describe the ability of a halide ion to act as a reducing agent going down the group

ability to behave as a reducing agent increases

as ions get bigger the outer electron is more shielded from the nucleus so easier to donate electron

Q: Why is chloride ion a weaker reducing agent then bromide ion?

chlorine is smaller ion

outer electron is less shielded from nucleus

stronger EFA so harder to donate electron

Describe how the displacement of halide ion happens

concentrated sulphuric acid donates hydrogen ion to halide ion to produce hydrogen halide

What do halide ions act as during displacement?

bases - proton acceptor

What does sulphuric acid act as during displacement?

proton donor

1. Write an equation for the reaction between sulphuric acid and sodium fluoride

2. state observation

3. Why does the reaction stop here for fluoride and chloride ions and how is this different fit bromide and iodide?

NaF(s) + H₂SO₄(aq) → NaHSO₄(aq) + HF(g)

HF = misty fumes

not strong enough reducing agents to reduce sulfuric acid

Bromide and iodide ions can reduce sulphuric acid

What do bromide ions reduce sulfuric acid to?

sulfur dioxide

State displacment and Redox equation of reduction of sulphuric acid to sulphur dioxide using sodium bromide

State oxidant and reducing agents

D: NaBr(s) + H₂SO₄(aq) → NaHSO₄(aq) +HBr(g)

(2e- + 2H⁺ + H₂SO₄ → SO₂ + 2H₂O
2Br- → Br₂ + 2e-

R: 2H⁺ + H₂SO₄ + 2Br^- → SO₂ + Br₂ + 2H₂O

OA = sulfuric acid
RA = bromide ion

How is sulfur dioxide gas identified?

choking gas

How is bromine identified?

brown gas

Combine the displacement and redox reaction of sodium bromide and sulphuric acid

D: 2NaBr(s) + 2H₂SO₄(aq) → 2NaHSO₄(aq) +2HBr(g)

R: 2HBr + H₂SO₄ → SO₂ + Br₂ + 2H₂O

→ 2NaBr + 3H₂SO₄ → 2NaHSO₄ + SO₂ + Br₂ + 2H₂O

What do iodide ions reduce concentrated sulphuric acid to?

sulfur dioxide then sulfur then hydrogen sulfide

How is sulfur identified?

yellow solid

How is hydrogen sulfide identified?

rotten egg smell

How is iodine identified?

purple vapour

Write a displacement equation of iodide sodium iodide and conc sulphuric

Q: Write a redox equation illustrating how I^- ions reduce concentrated sulphuric acid to sulfur dioxide

D: NaI(s) + 2H₂SO₄(aq) → NaHSO₄(aq) +HI(g)

(2e- + 2H+ → H₂SO₄ → SO₂+ 2H₂O
2I^- → I₂ + 2e^-

R: 2H⁺ + 2I^- + H₂SO₄ → SO₂ + I₂ + 2H₂O

Q: Write a redox equation illustrating how I^- ions reduce concentrated sulphuric acid to sulfur

R: 6H⁺ + 6I^- + H₂SO₄ → S + 3I₂ + 4H₂O

pg6

Q: Write a redox equation illustrating how I^- ions reduce concentrated sulphuric acid to hydrogen sulfide

R: 8H⁺ + 8I^- + H₂SO₄ → H₂S + 4I₂ + 4H₂O

Q: Write an equation showing overall reaction of KI with concentrated sulphuric acid to form hydrogen sulfide

displacement + reduce (pg7)

D: 8KI + 8H₂SO₄ → 8KHSO₄ + 8HI

R: 8HI + H₂SO₄ → H₂S + 4I₂ + 4H₂O

8KI + 9H₂SO₄ → 8KHSO₄ + H₂S + 4H₂O + 4I₂

Test for halide ions

silver nitrate solution

Describe the test for halide ions

dilute nitric acid

silver nitrate solution

dilute ammonia

concentrated ammonia

Why is dilute nitric acid used when testing for halide ions

remove other ions interfering with the test like carbonate or hydroxide ions

What is formed if carbonate ions are present?

Ag₂CO₃ (s)

How does nitric acid remove other ions?

2H+ + CO₃^2- → CO₂ + H₂O

H+ + OH^- → H₂O

Property of AgF

soluble

Describe what happens when testing for halide ions when NaF(aq) is tested

addition of silver nitrate: nvr as AgF is soluble

dilute NH₃: solution stays colourless

conc NH₃: solution stays colourless

Describe what happens when testing for halide ions when NaCl(aq) is tested

addition of silver nitrate: white ppt AgCl

dilute NH₃: white ppt dissolves to colourless solution

conc NH₃: white ppt dissolves to colourless solution

Describe what happens when testing for halide ions when KBr(aq) is tested

addition of silver nitrate: cream ppt AgBr

dilute NH₃: cream ppt does not dissolve

conc NH₃: cream ppt dissolves to colourless solution

Describe what happens when testing for halide ions when NaI(aq) is tested

addition of silver nitrate: yellow ppt AgI(s)

dilute NH₃: yellow ppt does not dissolve

conc NH₃: yellow ppt does not dissolve

Q: Write an ionic equation illustrating how a white ppt is formed when AgNO₃ is added to KCl(aq)

Ag⁺(aq) + Cl^-(aq) → AgCl(s)

(KCl (aq) + AgNO₃(aq) → KNO₃ + AgCl(s)
K⁺ Cl- + Ag⁺ NO₃^-
K⁺ NO₃^- + AgCl)

Why is ammonia solution used?

confirmatory tests

Explain reactions of ammonia to test for halide ions

AgCl is soluble in dilute ammonia

AgBr is sparingly soluble in solute ammonia but is soluble in concentrated ammonia

AgI is insoluble in dilute and concentrated ammonia

Why is Hal not used to acidify solution?

contains chloride ions which would form a white ppt when added to silver nitrate

Q: Write and equation illustrating the observation that occurs when dilute NH₃(aq) is added to AgCl(s) a white ppt

AgCl(s) + 2NH₃(aq) → [Ag(NH₃)₂]⁺ + Cl^-

*reaction of chlorine with water