3.1.3 - The Halogens Flashcards
What is the colour and state of fluorine?
Pale yellow gas.
Colour and state of chlorine?
Green gas
Colour and state of bromine?
Red/brown liquid
Colour and state of iodine?
Grey solid.
What do Halogens exist as?
Diatomic molecules.
What happens to their boiling and melting points down the group?
They increase due to increased strength of London forces as the size and relative mass of the atoms increase.
Are halogens oxidised or reduced?
Reduces therefore oxidising agents.
What do halogen form when they react?
1- ions.
Why are atoms less reactive as you go down the group?
Atomic radii increases which means outer electrons are more shielded from the attraction of the positive nuclei, as there are more inner electrons. This makes it harder for larger atoms to attract the electron needed to form an ion……
What happens during a displacement reaction?
There is a colour change.
Example of organic solvent?
Hexane
How can you see a displacement reaction?
Shake the mixture with an organic solvent. The halogen present will dissolve readily in the organic solvent which settles out as a distinct layer above the aqueous solution.
What colour is chlorine water?
Colourless.
What colour is bromine water?
Yellow
What colour is iodine solution?
Orange / brown.
When will a halogen displace a halide?
If it is below it in the periodic table.
What colour is bromine in organic solutions?
Orange
What colour is iodine in organic solvent?
Purple
How do you test for halogens?
Add dilute nitric acid to remove ions which might interfere with the reaction then add silver nitrate solution.
What is a further test you can do to test for halogens?
Add ammonia solution to test for solubility.
What does Cl- do when tested?
White precipitate, dissolves in dilute NH3.
What does Br- do when tested?
Cream precipitate, dissolved in concentrated NH3.
What is the result of I- when tested?
Yellow precipitate, insoluble in concentrated NH3.
What is disproportionation?
Oxidation and reduction of the same element.
What is the equation for sodium hydroxide and chlorine?
2NaOH + Cl2 -> NaClO + NaCl +H2O
What is sodium chlorate also called?
Bleach
What is the equation for the reaction between chlorine and water?
Cl2 + H2O -> HCl + HClO (chloric acid)
What do chlorate ions do?
Kill bacteria so to make it safe to drink and swim in.
What is chlorine important in water treatment?
- Kills disease causing microorganisms.
- Prevents the reinfection as chlorine remains in water.
- Prevents regrowth of algae, eliminating bad smells and tastes as well as removing discolouration caused by organic compounds.
What are the risks of using chlorine in water treatment?
- Harmful gas which irritates respiratory system.
- Liquid chlorine on the skin or eyes can cause severe burns.
- Chlorine can react with organic compounds in water producing chlorinated hydrocarbons, many of which are carcinogenic.
What are the two alternatives to chlorine?
Ozone (O3), or ultraviolet light.
How can ozone be used?
It is a strong oxidising agent which makes it great at killing microorganisms, however it is expensive to produce and the short half-life in water means the treatment isn’t permanent.
How can ultraviolet light be used?
It kills microorganism by damaging DNA, but it is ineffective in cloudy water, and won’t stop water being contaminated further down the line.
