Halogens

Question 1

The colour of halogens and physical state at room temperature

Answer 1

Fluorine: pale yellow, has

Chlorine: green, gas

Bromine: red-brown, liquid

Iodine: grey, solid

Question 2

Solubility

Answer 2

They have a low solubility in water as they’re non polar molecules

Dissolve easily in organic compounds like hexane. Some of resulting solutions which have distinctive colours :

• chlorine in water and in hexane is colourless
• bromine in water is yellow/orange and in hexane it’s orange/red
• iodine in water is brown and in hexane it’s pink/violet

Question 3

Halogens get less reactive down the group

Answer 3

As you go down the group atoms become larger so their outer electrons are further away from the nucleus

More shielding makes it harder for larger atoms to attract the electron needed to form an ion so larger atoms are less reactive and reactivity decreases down the group

Question 4

Electronegativity decrease down the group

Answer 4

There is more shielding

There is great increase in distance between nucleus and bonding electrons

Question 5

Melting and boiling points increase down the group

Answer 5

There is an increase of electron shells as you go down the group therefore London forces between halogens get stronger

Increasing London forces makes it harder to overcome the intermolecular forces so melting and boiling points increase

Question 6

Halogens can displace halide ions from dilution

Answer 6

This is a displacement reaction

Halogens relative oxidising strength can be seen in displacement reaction with halide ions

In these reactions more reactive halogen with replace less reactive halide in solution:

• chlorine displaces bromide and iodide ions
• bromine displace iodide ions
• iodine doesn’t displace anything

Question 7

Reaction with group 1 metals

Answer 7

2Li + F —

Question 8

Reaction with group 2 metals

Answer 8

Mg + Cl2 —

Question 9

Reducing power of halides increase down the group

Answer 9

Halide ions can act as reducing agent by losing an electron from its outer shell

How easy it is depends on the attraction between halides nucleus and outer electrons. As you go down the group it gets weaker because:

• ions get bigger so electrons are further away from nucleus
• extra inner electron shells so there’s greater shielding effect

Question 10

Hydrogen halides are acidic gases

Answer 10

They can dissolve in water to produce misty fumes of acidic gas ( turn damp blue litmus paper red)

HCl forms hydrochloric acid
HBr forms hydrobromic acid
HI forms hydroiodic acid

Question 11

Silver ions react with halide ions to form a precipitate

Answer 11

1) First add dilute nitric acid to remove ions that may interfere with the reaction
2) Add silver nitrate solution
3) A precipitate is silver halide is formed

Colour of precipitate identifies halide present in original solution :

• Fluoride, no precipitate as it’s soluble
• chloride, white precipitate
• bromide, cream precipitate
• iodide, yellow precipitate

The precipitate may look similar so you can add ammonia solution:

• AgCl, precipitate dissolves giving colourless dilution
• AgBr, precipitate does change unless it’s dissolved in Conc. ammonia solution to give colourless solution
• AgI, precipitate doesn’t dissolve even in Conc. ammonia