3.2.3 Group 7 - halogens

Question 1

What is the trend in electronegativity of the halogens?

Answer 1

Electronegativity decrease down the group

• electronegativity is a measure of the ability of an atom to attract electrons towards itself in a covalent bond
• atoms get larger down the group, so the shared electrons in the covalent bond get further away from the halogen nucleus

shielding increases with more inner shells of electrons.

• attraction between the shared electrons and the halogen nucleus gets weaker

Question 2

What is the trend in boiling point of the halogens?

Answer 2

Boiling point increase down the group- atoms get larger down the group - van der Waals forces between molecules stronger- more energy to break

Question 3

Displacement reactions of halide ions in aqueous solution

Answer 3

Halogens react with metal halides in a solution- the halide in the compound will be displaced by a halogen of higher oxidising ability/reactivity
-not a less reactive one.

Question 4

What is the trend in the oxidising ability of the halogens?

Answer 4

the oxidising ability of the halogens decreases down the group:
F2 > Cl2 > Br2 > I2

Question 5

What is the trend in reducing the ability of the halide ions?

Answer 5

reducing the ability of the halide ions to increase down the group:
F- < Cl- < Br- < I-

Question 6

The reaction of solid sodium chloride with concentrated sulfuric acid

Answer 6

Steamy fumes of hydrogen chloride are seen:(acid-base)
NaCl(s) + H2SO4(l) -> NaHSO4(s) + HCl(g)

Question 7

The reactions of solid sodium bromide with concentrated sulfuric acid

Answer 7

Steamy fumes of hydrogen bromide &brown fumes of bromine-colourless sulfur dioxide are also formed. (acid-base)
NaBr(s) + H2SO4(l) -> NaHSO4(s) + HBr(g)
Redox - 2H+ + 2Br- + H2SO4(l) -> SO2(g) + 2H2O(l) + Br2(l)
Br is a reducing agent for sulfur

Question 8

How to identify and distinguish between halide ions?

Answer 8

Add acidified silver nitrate solution:
F- no precipitate
Cl- a white precipitate of silver chloride.
Br- cream precipitate of silver bromide.
I- pale yellow precipitate of silver iodide

Question 9

Why is silver nitrate solution used to identify halide ions?

Answer 9

All metal halides (except fluorides) + aqueous silver ions in silver nitrate solution - form a precipitate the insoluble silver halide

Question 10

Why is the silver nitrate solution acidified?

Answer 10

get rid of any soluble carbonate or hydroxide impurities
interfere with the test by forming insoluble silver carbonate or silver hydroxide.

Question 11

What is the trend in solubility of the silver halides in ammonia?

Answer 11

Silver chloride dissolves in dilute ammonia.
Silver bromide dissolves in concentrated ammonia.
Silver iodide is insoluble in concentrated ammonia.

Question 12

Why is ammonia solution added to silver halides?

Answer 12

tell which silver halide has formed- colours can be similar

Question 13

What is the reaction of chlorine with water to form chloride ions and chlorate(I) ions? What is the reaction of chlorine with water to form chloride ions and oxygen?

Answer 13

Cl2(g) + H2O(l) <-> HCl(aq) + HClO(aq)
in sunlight:
2Cl2(g) + 2H2O(l) <-> 4HCl(aq) + O2(g)

Question 14

Give one use of chlorine

Answer 14

Water treatment: chlorine is used to purify water and in swimming baths, to prevent life-threatening diseases. (kill microorganisms)

Question 15

What is the reaction of chlorine with cold, dilute, aqueous NaOH?

Answer 15

Cl2(g) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) + H2O(l)

Question 16

What is NaClO used for?

Answer 16

It is an oxidising agent and the active ingredient in household bleach