Group 7 And Uses Of Chlorine And Chlorate Flashcards
(35 cards)
Describe the trend in boiling point down Group 7 and explain why this occurs.
Boiling point increases down the group. This is because larger molecules have more electrons, leading to stronger van der Waals forces.
State the physical state at room temperature of each of the first four halogens.
F2 - gas
Cl2 - gas
Br2 - liquid
I2 - solid
Describe the trend in electronegativity down Group 7 and explain it.
Electronegativity decreases down the group because there are more shells, leading to increased shielding and less nuclear attraction to bonding electrons.
How does reactivity change down
Group 7 and why?
Reactivity decreases down the group due to larger atoms and more shielding, leading to weaker oxidising ability.
State the displacement rule for halogens.
A more reactive halogen displaces a less reactive halide from solution.
Complete the following displacement observations:
E.g. 1. Cl₂ added to Br⁻ and I⁻:
• Chlorine (Cl₂) is more reactive than both bromide (Br⁻) and iodide (I⁻).
• So Cl₂ displaces both:
• Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ → orange solution (Br₂ formed)
• Cl₂ + 2I⁻ → 2Cl⁻ + I₂ → brown solution (I₂ formed)
🟢 Answer: Orange (Br₂), Brown (I₂)
• Cl₂ added to Br⁻ and I⁻:
A: Orange (Br₂), Brown (I₂)
• Br₂ added to I⁻:
A: Brown (I₂)
• I₂ added to Br⁻ or Cl⁻:
A: No reaction
Write the ionic equations for the following reactions:
• Chlorine and bromide:
A: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
• Bromine and iodide:
A: Br₂ + 2I⁻ → 2Br⁻ + I₂
What is formed when chlorine reacts with cold dilute NaOH? Write the balanced equation.
A: Cl₂ + 2NaOH → NaCl + NaClO + H₂O
State the oxidation states of chlorine in the above reaction.
Cl: 0 → -1 (reduction in NaCl), 0 → +1 (oxidation in NaClO)
Write the equation for the disproportionation of chlorine with water.
Cl₂ + H₂O ⇌ HCl + HClO
What happens to chlorine in sunlight in water?
Cl₂ + H₂O → 2HCl + ½O₂ (chlorine decomposes water
Give three benefits of using chlorine to treat water.
• Kills bacteria
• Prevents reinfection
• Removes tastes, odours, and discolouration
State three risks associated with chlorine use in water.
• Toxic gas (respiratory damage)
• Can form carcinogenic chlorinated hydrocarbons (e.g., CH₃Cl)
• Must balance risk vs public health benefit (e.g., cholera prevention)
Name the elements in Group 7.
Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)
What type of molecules are halogens and what type of ions do they form?
Diatomic molecules (X₂); form 1- ions (X⁻) by gaining 1 electron (reduction)
State appearances of halogens at room temperature
Formula and Appearance at Room Temp
F₂- Pale yellow gas
Cl₂ - Green gas
Br₂ - Red-brown liquid (orange vapour)
I₂ - Grey solid
Why does boiling point increase down Group 7?
Due to larger molecular size and mass, stronger London dispersion forces require more energy to overcome
Explain why electronegativity decreases down Group 7.
Although nuclear charge increases, the increase in atomic radius and shielding reduces the attraction for bonding electrons.
Describe the trend in oxidising power down the group.
Oxidising power decreases down the group. Fluorine is the strongest oxidising agent, iodine is the weakest.
How does reducing power of halide ions change down the group?
Reducing power increases down the group due to larger ionic radius and increased shielding, making it easier to lose electrons.
Describe what happens when NaF and NaCl react with concentrated H₂SO₄.
Only HF or HCl is formed (misty fumes); no redox reaction.
Describe what happens when NaBr reacts with concentrated H₂SO₄.
HBr → Br₂ + SO₂ + H₂O. Orange fumes of Br₂ and choking SO₂ gas.
Redox: S⁺⁶ → S⁺⁴; Br⁻ → Br₂
Describe what happens when NaI reacts with concentrated H₂SO₄.
HI → I₂ + SO₂ + S + H₂S
Observations: Purple/black solid (I₂), bad-smelling H₂S
Redox: S⁺⁶ → S⁺⁴, 0, -2; I⁻ → I₂
Outline the steps for testing halide ions.
- Add dilute nitric acid to remove carbonate ions
- Add silver nitrate (AgNO₃).
