Redox and Halides Flashcards
(35 cards)
Define oxidation state
How many electrons are lost or gained from being an atom
Define disproportionation reaction
Describes a reaction when one element is simultaneously oxidised and reduced in the same reaction
The same element appears twice in the products
What are the oxidation states of oxygen in compounds?
Usually -2 If in a peroxide, H2O2, it is -1 OF2 is +2 O2F2 is +1 O2 is 0
What is the oxidation state value of every element
Zero
What are Hydrogens oxidation states
Usually +1
When with a metal it is -1
When H2 it is 0
When is chlorides oxidation state positive
When with a negative oxygen
It is usually -1
What is a reducing agent
An electron donor
The substance being oxidised
What is an oxidising agent
An electron acceptor
The substance being reduced
If a substance in oxidised, how does it charge change?
It gets more positive as electrons are lost
If a substance is reduced, how does its charge change
It gets more negative as electrons are gained
What are the five steps when writing full half equations?
Calculate oxidation states Balance the element Sort the electrons Balance the oxygen using H2O Balance the hydrogen using H+ ions
If you are told it is an acidic solution, what must the half equation contain?
H+ ions
What are halogens
Soluble salts
Highly reactive
Non metals
Group 7 elements
State the halogens and their properties
Fluorine: pale yellow gas
Chlorine: green yellow gas
Bromine: red/brown liquid
Iodine: black solid
Give more detailed properties of iodine
When heated to vapour, it is purple
Does not dissolve in water but makes a brown solution with aqueous potassium iodide
Will dissolve in a non-polar solvent
Iodine turns blue/black with starch
State the trend in boiling point of the halogens
Increases down the group
Increasing strength van der Waals as size and relative mass of each atom increases
State the trend in electronegativity of the halogens
Decreases down the group
All highly electronegative
Larger atoms attract shared electrons less than smaller ones (as atoms increase in size, electronegativity decreases)
Which halogen is the strongest oxidising agent
Fluorine
Higher up the group, less shielding, smaller, more easily attracts electrons
What are the general steps and observation when testing for Cl, Br and I ions
1) acidify with HNO3: reacts with impurities I.e. Carbonates which may cause false positive, cannot use HCl as it contains chloride ions
2) add AgNO3: forms a precipitate, Cl is white, Br is cream and I is yellow
3) add dilute ammonia: AgCl redissolves, no change in others
4) add conc ammonia: AgCl and AgBr redissolve, not change in AgI
What are the general steps and observations when testing for F ions
When HNO3 and AgNO3 are added, it forms a colourless solution as AgF is soluble in water
How do you test for sulphate ions
Add HNO3
Add BaCl2
White precipitate BaSO4 forms
Ba+2 + SO4-2 = BaSO4
What happens when a halide ions reduces another substance and what is the half equation for this reaction?
The halide oxidised to a halogen
2X- = X2 +2e-
When a halide is used to reduce a substance, what are the reagents that are usually used to react with conc sulphuric acid
Sodium chloride, sodium bromide, sodium iodide
Some halide ions are strong enough reducing agents to reduce sulphuric acid to water and sulphur along with the halogen
Which halides reduces sulphuric acid and to what?
Cl does not reduce it
Br reduces it from S(+6) to S(+4)
I reduces it from S(+6) to S(-2)
