Group 7 Flashcards
What is the trend in electronegativity in the halogens? Why?
Decreases down the group. Larger atoms attract electrons less than smaller ones, electrons further from nucleus and shielded by more electrons.
What is the trend in boiling point down group 7? Why?
Increases down the group. Due to increasing strength of Van der Waals forces as size and relative mass of molecules increases.
Trend in oxidising ability in the halogens?
Halogens become less oxidising down the group. A halogen will displace a halide from the solution it the halide is below it in the periodic table.
Trend in reducing ability in the halogens?
Increases as you go down the group
Reaction of sodium fluoride with sulphuric acid
NaF + H2SO4 → NaHSO4 + HF
Reaction of sodium chloride with sulphuric acid
NaCl + H2SO4 → NaHSO4 + HCl
Reaction of sodium bromide with sulphuric acid (2)
NaBr + H2SO4 → NaHSO4 + HBr
2HBr + H2SO4 → Br2 + 2H2O
Reaction of sodium iodide with sulphuric acid (3)
NaI + H2SO4 → NaHSO4 + HI
2HI + H2SO4 → l2 + SO2 + 2H2O
6HI + SO2 → H2S + 3I2 + 2H2O
Silver nitrate used to test for what ions and how?
Test for halides
1) add dilute nitric acid to remove ions which may interfere
2) add silver nitrate solution
Precipitate forms
F- none Cl- white Br- cream I- yellow
Why is silver nitrate used?
Silver ions combine with halide ions to produce silver halide precipitates
Why is silver nitrate acidified for testing for ions?
Prevents unreacted OH- ions from reacting with silver ions to give an unrecognisable precipitate.
Why is ammonia solution added to precipitates of silver halides
To confirm, by checking the solubilities of the halides
What happens when you add NH3 to CI - precipitate
Dissolves white precipitate
What happens when you add concentrated NH3 to br- precipitate
Cream precipitate dissolves
What happens when you add concentrated NH3 to I- precipitate
Yellow precipitate remains as it’s insoluble
Reaction of chlorine with water
Chlorine undergoes disproportionation resulting in a mixture of chlorine and chlorate ions
Cl2 + H2O ⇌ 2H⁺ + Cl⁻ + ClO⁻
Decomposition reaction of chlorine in sunlight in water
Produces chloride ions and oxygen
2Cl2 + H2O ⇌ 4H⁺ + 4Cl⁻ + O2
What do chlorate ions do?
Kill bacteria
Advantages of using chlorine in water treatment (3)
Kills disease-causing microorganisms
Some persists in water and prevents infection further down supply
Prevents growth of algae, removing bad tastes and smells as well as colour due to organic compound
Disadvantages of using chlorine in water treatment.(2)
Chlorine gas is harmful when breathed in. Liquid chlorine on skin or eyes can cause severe chemical burns
Water contains organic compounds which could chlorinated hydrocarbons which can be carcinogenic
Benefits of water treatment outweigh toxic effects.
Reaction of chlorine gas with cold, dilute, aqueous NaOH
Product is sodium chlorate(I) solution NaClO - bleach
2NaOH + Cl2 → NaClO + NaCl + H2O
Chlorine is oxidised and reduced - disproportionation
Uses of NaClO - bleach
Water treatment, bleaching paper and textiles and cleaning
What is the test for ammonium ions?
- Add NaOH to produce ammonia gas
- Red litmus paper turns blue
NH4⁺ + OH⁻ → NH3 + H2O
OH⁻ test
Dip a piece of litmus paper, in presence of hydroxide ions, red litmus paper turns blue
