Group 7 the Halogens Flashcards
as chem
Describe the colours of the group 7 halogens?
Flourine- pale yellow gas
Chlorine- greenish reactive gas
Bromine- red liquid
Iodine- shiny grey solid
Describe boiling point trend down group..
This increases as we go down the group. This is because the van der waals forces increase due to the increasing size and relative mass of the atoms.
The physical state goes from gas at the top of group 7 to solid at the bottom.
What happens in a displacement reaction?
A more reactive halogen will displace a less reactive halogen.
the halogen on its own is what colour you would observe
Describe electronegativity..
This decreases as we go down the group. Electronegativity is the ability for an atom to attract electrons towards itself in a covalent bond. The atoms get larger and the distance between the positive nucleus and bonding electrons increases. There is also more shielding.
What are the colours observed displacement reactions of halide ions?
Chlorine: pale green solution
Bromine: Yellow solution
Iodine : Brown solution
What reaction produce bleach?
2NaOH + Cl–> NaCLO +NaCl +H20
Chlorine reacting with dilute cold NAOH solution
How can water be sterilised write the equation?
Adding chlorine to water can kill bacteria in water.
The disproportionate reaction:
Cl 2+H20–>2H+ +Cl- + ClO-
Why does sunlight disturb water sterilisation?
Changes the products made in water and chlorine reaction
2H20 +Cl2–> 4H+ + 2Cl- + 02
no CLO- produced
What are the advantages and disadvantages of chlorinating drinking water?
ADVANTAGES:
Destroys microorganisms that cause disease
Long lasting so reduces bacteria build up further down the supply.
Reduces the growth of algae that discolours water and can give it a bad smell and taste.
DISADVANTAGES:
Chlorine gas is toxic and irritates the respiratory stystem.
Liquid chlorine causes severe chemical burns to the skin.
Chlorine can react with organic compounds present in the water to make chloroalkanes.
These have been linked with causing cancer. However the risk of not chlorinating water could lead to a cholera epidemic.
Describe the reducing power of halide ions?
As halide ions lose an electron in reactions they are reducing agents.
As we go down the group the ionic radius increases.
The distance between the nucleus and outer electrons becomes larger and there is more shielding. The attractive force gets weaker.
The outer electron is lost more readily and this is the reason why I is a more powerful reducing agent than F-
What are the 2 tests that can be used to prove the reducing power of halide ions trend (increases down group 7)
1) reaction with sulphuric acid
2) reaction with silver nitrate solution
Describe reaction of halide ions with silver nitrate?
1) Add nitric acid and then silver nitrate solution
2) the colour of precipitate formed indicates the halide.
Colours:
Chlorides= White
Bromides= Cream
Iodides= Pale yellow precipitate
3) Conduct a further test with ammonia
What is the equation between reaction of halide ions with silver nitrate?
Ag+ +Cl- –> Agcl (s)
Ag+ +Br- –> AgBr
Ag+ +I- –> AgI
Describe conduction of further test to identify halide ions after reacting with silver nitrate?
1) Add ammonia (nh3)
Adding dilute ammonia results:
- Silver chloride dissolves in dilute ammonia to form complex ion
- Silver Bromide dissolves in concentrated ammonia
- Silver Iodide is insoluble so does not react with concentrated ammonia
