3.1.3 The halogens (and halides) Flashcards
describe the trend in melting and boiling points of the halogens
The m.p. and b.p. increase going down the group as shown by F2 and Cl2 being gases, Br2 being a liquid and I2 and At2 being solids at rooms temperature.
Explain the trend in melting and boiling points of halogens
They increase down the group because the london forces between the molecules get stronger down the group becuase there are more electrons and so more energy is require to break them.
describe the trend in reactivity of halogens
Reactivity decreases down the group, as it becomes more difficult for the atom to gain an electron.
explain what is meant by halogen displacement
more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
what are the colours of the halogens in water
Cl2 = chlorine = colourless
Br2 = bromine = yellow
I2 = iodine = brown
what are the colours of halogens in cyclohexane
Cl2 = colourless
Br2 = orange
I2 = purple
what is the colour of the cyclohexane layer after the addition of KBr to a chlorine solution
orange
what is the colour of the cyclohexane layer after the addition of KI to a chlorine solution
pink
what is the colour of the cyclohexane layer after the addition of KCl to a Bromine solution
orange
no change
what is the colour of the cyclohexane layer after the addition of KI to a bromine solution
purple
what is the colour of the cyclohexane layer after the addition of KCl to a iodine solution
purple
no reaction
what is the colour of the cyclohexane layer after the addition of KI to a iodine solution
purple
no reaction
explain the trend in reactivity of halogens
Going down the group the atomic radius increases, there are more inner shells so more shielding and less nuclear attraction to gain an electron so reactivity decreases
Benefits and risks of using chlorine
helps make water safe to drink as it kills bacteria but chlorine is a toxic gas that causes respitory irritant in small concentrations and can be fatal in large ones.
Chlorine can react with hydrocarbons to produce chlorinated hydrocarbons which are suspected of causing cancer. However the overall risk to health of not adding chlorine outweighs the risk of chlorinated hydrocarbons.
how are halide ions tested for
Add silver nitrate to a solution containing a halide. Then add ammonia (NH3)
what happens when silver nitrate is added to chloride
then follow on with any other addatives and consequences
a white precipitate is formed.
If dilute NH3 is then added the precipitate will disolve
what happens when silver nitrate is added to bromide
then follow on with any other addatives and consequences
a cream precipitate is formed
This precipitate will dissolve in concentrated NH3
what happens when silver nitrate is added to iodide
follow on with any other addatives and consequences
a yellow precipitate is formed
This precipitate will not dissolve in either dilute nor concentrated NH3
