Group 7: Trends, water, bleach Flashcards
How does the boiling point of halogens change as you go down the group and why?
- Boiling point increases as you go down group.
- Increased size of molecules as you go down group due to increased Mr.
- More/ increased Van der Waals forces as you go down the group.
What is the trend in electronegativity as you go down group 7?
- Electronegativity decreases as you go down group.
- Atoms get larger, distance between positive nucleus and electrons in bond increase.
- More electronic shielding.
- Halogen atom will have less of ability to attract bonding electrons in the covalent bond.
How does halogen reactivity change as we go down group 7?
- Decreases.
- As atoms get larger, so more difficult to gain an electron.
What is the trend in oxidising ability of halogens as you go down the group?
- Oxidising ability decreases as you go down group (ie. its ability to oxiside another species by being reduced itself.)
Give the colours and states (at room temperature) of fluorine, chlorine, bromine and iodine.
Fluorine: Pale yellow gas.
Chlorine: Pale green gas.
Bromine: Brown-orange liquid.
Iodine: grey solid.
In what solutions do displacement reactions of halide ions using more reactive halogens occur in?
- Aqeous solutions
Write full and ionic equation/ colour change expected for this reaction
KBr (aq) + Cl₂ (aq) –>
KBr = colourless
2KBr (aq) + Cl₂ (aq) –> 2KCl (aq) + Br₂ (aq)
Cl₂ + 2Br⁻ –> 2Cl⁻ + Br₂
Br₂ = orange solution
Write equation for reaction of cold, dilute aqueous NaOH with chlorine.
2NaOH (aq) + Cl₂ (g) –> NaClO (aq)+ NaCl (aq) + H₂O (l)
What are the conditions needed for NaOH to react with Cl2 to form bleach?
- NaOH must be cold, dilute and aqeueous.
What is the chemical name for bleach? Give its formula.
- Sodium chlorate (I)
- NaClO
What type of reaction is bleach/ sodium chlorate (I) made in? What does this mean?
- Made in disproportion reaction
- Cl₂: oxidation state = 0 (on left hand-side of equation), Cl in NaClO has oxidation state of +1.
- Cl in NaCl has oxidation state of -1.
- So, chlorine has simultaneously been oxidsed/ reduced. Disproportion reaction.
What is a disproportion reaction?
- Reaction where a species is simultaneously oxidised and reduced.
Give 3 different uses of sodium chlorate (I)/ bleach.
- Treating water
- Bleaching paper/ fabrics
- Cleaning agents
How does adding Cl2 to water (in drinking water/ water in swimming pools) actually kill microbes within the water?
- ## Adding Cl2 to water will produce ClO⁻ ions (chlorate ions), which will kill microbes.
Write overall/ ionic equation for H2O reacting with Cl2, WITHOUT the presence of sunlight. What type of reaction is this known as and why?
Gautum notes 05/03/25
- IONIC: H₂O (l) + Cl₂ (g) – (reversible reaction –> 2H⁺ (aq) + Cl⁻ (aq) + ClO⁻ (aq)
- OVERALL: Cl₂ (g)+ H₂O (l) — (reversible reaction sign) –> HCl (aq) + HClO (aq)
- Disproportionation reaction: chlorine has been simulatenously reduced/ oxidised.
- Cl2 (Cl has oxidation state of 0) –> has oxidation state of +1 in chlorate ion, has oxidation state of -1 in Cl-.
Write overall/ ionic equation for H2O reacting with Cl2, WITH the presence of sunlight. Explain how the reaction differs to WITHOUT presence of sunlight.
Gautum notes 05/03/25
- IONIC: 2H₂O (l) + 2Cl₂ (g) –> 4H⁺ (aq) + 4Cl⁻ (aq) + O₂ (g)
- Overall: 2Cl₂ (g)+ 2H₂O (l) —> 4HCl (aq) + O₂ (g)
- No ClO⁻ ions made in reaction with presence of sunlight.
- The sunlight will decompose the ClO⁻ ions.
What are the advantages of chlorinating drinking water?
3 main advantages.
- Destroys micro-organisms that cause disease.
- Long-lasting so reduces bacteria build up further down the supply.
- Reduces the growth of algae that discolours water and can give it a bad smell/ taste.
What are the disadvantages of chlorinating drinking water? Why do we chlorinate drinking water if there are all of these disadvantages?
- Chlorine gas is toxic, irritates respiratory system.
- Liquid chlorine causes severe chemical burns to skin.
- Chlorine can react with organic compounds in water to make chloroalkanes; linked with causing cancer.
- Why: only used in small amounts
Give overall equations for reaction of chlorine with water in sunlight vs without sunlight.
Gautum notes: 05/03/25
- In sunlight: 2Cl₂ (g) +2H₂O (l)> 4HCl (aq) + O₂ (g).
- Without sunlight: Cl₂ (g) + H₂O (l) — (reversible reaction sign) –> HCl (aq) + HClO (aq)
