redox and group 7 Flashcards
What are the properties of flourine?
- yellow gas
- very reactive
- toxic
what are the properties of chlorine?
- green gas
- very reactive
- toxic
what are the properties of bromine?
- orange liquid
- very reactive
- toxic
- often used as a solution in water
what are the properties of iodine?
- grey crystals
- reactive
- toxic
- used in solution as antiseptic
what is the trend in atomic radius down group 7?
- the atomic radius increases as there are more shells so more sheiling so bigger atoms.
what is the trend in electronegativity in down group 7?
- the electronegativity decreases as there are bigger atoms and more shells down the group which leads to more shielding so a weaker attraction between the nucleus and 2 electrons in a covalent bond.
what is the trend in melting and boiling point down group 7?
- the mpt and bpt increases down the group as there are more electrons so more van der Waals forces,
what happens in the displacement reaction between chlorine and bromide?
- yellow solution forms
- CL2+ 2BR- -> 2cl- + Br2
what happens in the displacement reaction between chlorine and iodide?
- Brown solution forms
- Cl2 + 2I- + 2Cl- + I2
what happens in the displacement reaction between Bromine and iodide?
- brown solution forms
- Br2+ 2I- -> 2Br- + I2
what is the trend in oxidising power in group 7?
- to be an oxidising agent in to gain electrons (taken from the oxidising species
- the oxidising power decreases down the group
why does the oxidising power decrease down the group?
- down the group it becomes harder to gain an electron because the atoms are larger and there is more shielding due to extra electron shells. so the foa between electrons and nucleus is reduced
what happens in the displacement reaction between chlorine and bromide when an organic solvent is added?
- yellow solution forms in organic layer
- cl2+2br- -> 2cl- +br2
what happens in the displacement reaction between chlorine and iodide? when an organic solvent is added?
- purple solution forms in organic layer
- cl2 + 2I- -> 2Cl- + I2
what happens in the displacement reaction between bromine and iodide? When an organic solvent is added?
- purple solution forms in organic layer
- Br2 + 2I- -> 2BR- + I2
what is the explanation for the displacement reaction between the halogen atom and halides of group 7?
- the halogen atom gains an electron when it oxidises the halide ion
- the smaller the halogen atom , the easier it is to gain an electron as it is smaller and has less shielding.
what is oxidation in terms of oxygen?
- adding oxygen e.g. magnesium is oxidised to magnesium oxide.
what is an oxidising agent?
- accepts/ recieves an electron from a reducing agent.
- getting reduced itself but is the oxidising agent.
what is reduction in terms of oxygen?
- removing oxygen e.g. copper oxide is reduced to copper
what is a reducing agent?
- lets reduction happen
- hydrogen is the reducing agent.
what is a redox reaction?
- a reaction where both reduction and oxidation occur
- no oxygen is involved
what does oil rig stand for?
- Oxidation
- Is a
- Loss of electrons
- Reduction
- is a
- Gain of electrons
what are oxidation states?
- oxidation states are a method for working out if a substance is oxidised or reduced
- every element in a compound is given an oxidation number
- changes in the oxidation number indicate if oxidation or reduction is happening.
what is the oxidation number of an element?
always 0
in what order do you create a balanced half equation?
- atoms
-ions
-charges - electrons
what is the oxidation number of a simple ion?
- the oxidation number of each element is the same as its charge
- e.g. NaCL -> Na= +1 Cl= -1
what is the oxidation number in a covalent molecule
- the oxidation number of each element is the same as its charge
what are the general rules for oxidation numbers?
- hydrogen = +1 unless joined to a metal -1
- group 1 = +1
- group 2 = +2
- aluminium = +3
- oxygen =-2
- fluorine = -1
- chlorine = -1
What is the oxidation state of SO4?
-2
How do you calculate the oxidation state of a compound where one of the oxidation states is unknown and does not follow a rule?
Look at the atomic number of the unknown element and determine how many e-s can be gained or lost to form a full outer shell. Then look at the oxidation state of the element you know
What happens in a reduction reaction involving a halide?
- When a halide ion reduces another substance the halide is oxidised to a halogen
what happens in the formation of hydrogen halides?
- NaX + H2So4 -> NaHSO4 + Hx
- e.g. NaCl +H2SO4 -> Na HSO4 +HCl
what is the trend in reducing power in group 7?
- the reducing power increases down the group.
- down the group it becomes easier to loose an electron because ions are larger and there is more shielding (due to extra electron shells.)
what is disproportionation?
- a reaction in which a substance is simultaneously oxidised and reduced.
- this happens when water is mixed with chlorite to form a mixture of chlorite and chlorate (1) ions are formed
what happens in the reaction of water and chlorine so that is it called disproportionate?
- chlorine is oxidised from a state of 0 in Cl2 to -1 in Cl-
- chlorine is also reduced from a state of 0 in Cl2 -> +1 in ClO -
- overall the oxidation state of chlorine remains at 0
what are the uses of chlorine I ions?
- chlorine 1 ions are used to kill bacteria in water treatments.
-2cl2 +2H20 (l) -><- 4H+ (aq) + 4Cl- (aq) + 02 (g)
What are the advantages of adding chlorine to drinking water?
- it can be used to kill bacteria and pathogens
- inhibits algal growth and removes smells bad tastes and discoloration
- prevents reinfection of water further down the supply by remaining in the water.
what are the disadvantages of using chlorine in drinking water?
- toxic and harmful gas that can irritate the respiratory system if inhaled
- forms chlorinated hydrocarbons such as dichloromethane when it reacts with organic compounds found in the water
What happens when you mix chlorine with cold, dilute, aqueous sodium hydroxide?
- Sodium chlorate (1) is formed aka bleach.
- This is a disproportionation reaction.
- reduced from 0 in cl 2 to +1 in NaClO
- oxidised from 0 in cl2 to -1 in naCL
- colourless solution
what happens if chlorine is bubbled through water in the presence of bright sunlight?
- 2Cl2 +2H20 (l) -><- 4H+ (aq) + 4Cl- (aq) + O2 (g)
how do you test for an ammonium ion?
- add dilute sodium hydroxide and gently heat if ammonium ions are present they will turn into ammonia gas. this will turn damp litmus paper red and universal indicator paper blue
how do you test for carbonate ions?
- add an acid
- carbon dioxide gas bubbles if carbonate ions are present
- lime water is used to confirm that the gas is carbon dioxide
- lime water test to see if gas is carbon dioxide
how do you test for sulfate ions?
- add a few drops of dilute hcl
- add a few drops of barium chloride
- a white precipitate of barium sulfate forms if sulfate ions are present.
why is HCl added in the test for sulfate ions?
- to remove any carbonate ions that might be present as they would also produce a white precipitate, giving a false positive result.
how do you test for hydroxide ions?
- test a 1 cm depth of solution in a test tube with red litmus paper or universal indicator paper. hydroxide will turn damp red litmus paper blue
