3.2.3 Group 7, the halogens Flashcards
How do boiling points change down Group 7?
Boiling points increase down the group
Due to stronger Van der Waals forces from increasing atomic size and number of electrons
What happens to the physical state of halogens down the group at room temperature?
They change from gases (top) to solids (bottom)
Define electronegativity.
The tendency/ability for an atom to attract a bonding pair of electrons towards itself in a covalent bond.
How does electronegativity change down Group 7?
Electronegativity decreases
Atomic radius increases & Shielding increases
Reduced the attraction between the nucleus and bonding electrons.
What is the trend in oxidising ability down Group 7?
Halogens become less oxidising as you go down the group
(Reactivity in halogens decreases down the group)
Because atoms get larger, more shielding and therefore weaker nuclear attraction.
What is formed in a reaction between Chlorine water and potassium bromide?
Orange solution (Br₂)
KCl formed
(Cl has displaced Br)
What is formed in a reaction between bromine water and potassium iodide?
Brown solution (I₂)
KBr has formes
(Br has displaced I)
What determines if a halogen can displace a halide?
A halogen can displace a halide ion if it is more reactive (higher up the group)
What type of reaction occurs when chlorine reacts with NaOH to make bleach?
A disproportionation reaction
What is the equation for making bleach from chlorine and NaOH?
Cl₂ + 2NaOH → NaCl + NaClO + H₂O
Why is the reaction to make bleach considered a disproportionation reaction?
Chlorine is simultaneously reduced (NaCl) and oxidised (NaClO)
What are the uses of bleach?
Treating water
Bleaching paper & fabrics
Cleaning agents
What happens when chlorine is added to water?
(give an equation)
Disproportionation reaction
Cl₂ + H₂O ⇌ HCl + HClO
What are the advantages of using chlorine in water sterilisation?
- Kills bacteria & microorganisms that can cause disease
- Removes bad taste/smell
- Reduces growth of algae
- Long lasting - so reduces bacteria build up further down supply.
What are disadvantages of chlorinated water?
- Chlorine gas is toxic and irritates the respiratory system
- Liquid chlorine causes severe chemical burns to the skin
- Chlorine can react with organic compounds to form chloroalkanes, has been linked to cancer.
What do halide ions acta as in reactions with sulfuric acid?
Reducing agents
Why do halides become more powerful reducing agents down the group?
Ionic radius increases down the group
Meaning more shielding and attractive forces between nucleus and outer electrons weaken
The outer electron is therefore more easily lost.
What is the equation and observation for the reaction between concentrated H₂SO₄ and NaOH?
H₂SO₄ + NaCl→NaHSO₄ + HCl
White misty fumes go HCl
Write the equation to show the redox reaction between NaBr and H2SO4 and state any observations.
Reduced: H₂SO₄ + 2H⁺ + 2e- → SO₂ + 2H₂O
Oxidised: 2Br- → Br₂ + 2e-
Overall Redox: H₂SO₄ + 2H⁺ + 2Br- → SO₂ + 2H₂O + Br₂
* Reddish-brown gas (Br₂)
* Colourless acidic gas (SO₂)
Write the 3 equations to show the redox reaction between NaI and H2SO4 and state any observations.
Reduced: H₂SO₄ + 2H⁺ + 2e- → SO₂ + 2H₂O
H₂SO₄+6H⁺+6e⁻→S+4H₂O
H₂SO₄+8H⁺+8e⁻→H₂S+4H₂O
Oxidised: 2I⁻ → I₂ + 2e⁻
Overall Redox for each:
H₂SO₄ + 2H⁺ + 2I⁻ → I₂ + SO₂ + 2H₂O
H₂SO₄+6H⁺+6I⁻→S+4H₂O+3I₂
H₂SO₄+8H⁺+8I⁻→H₂S+4H₂O+4I₂
* Violet/purple vapour (I₂)
* Yellow solid (S)
* Rotton egg smell (H₂S)
What is the test for halide ions, and how would you confirm?
Add dilute nitric acid, then silver nitrate.
Then, you can confirm using dilute & concentrated NH₃
What colour precipitates for with silver nitrates?
- Cl⁻: White ppt (dissolves in dilute NH₃)
- Br⁻: Cream ppt (dissolves in conc. NH₃)
- I⁻: Yellow ppt (insoluble in NH₃)
Describe the test for ammonium compounds using litmus paper.
- Add NaOH, gently heat and if ammonium compounds present, NH₃(g) will be produced
- Use damp red litmus paper
Positive result - Ammonia turns litmus paper blue
Why can hydroxides also be identified using litmus paper?
Hydroxides are alkaline and they will turn red litmus paper blue.
