AQA Chemistry A level QUESTIONS AND CORRECT
VERIFIED ANSWERS ALREADY GRADED A+ 100%
GUARANTEED PASS LATEST UPDATE \University of
Glasgow
what is the equation which links the colour and frequency of the light
absorbed with the energy difference between the split d orbitals
E = hv.
v = frequency of light absorbed (unit s-1 or Hz) h= Planck's constant 6.63 ×
10-34 (J s)
E = energy difference between split orbitals (J)
how can you change colour of transition metals
Changing a ligand or changing the coordination number will alter the
energy split between the d- orbitals, changing E and hence change
the frequency of light absorbed
describe the method of spectroscopy
• Add an appropriate ligand to intensify colour •Make up solutions
of known concentration (dilution series)
• Measure absorption or transmission
• Plot graph of absorption vs concentration •Measure absorption of
unknown and compare
,general trend of variable oxidation states
- Relative stability of +2 state with respect to +3 state increases across the
period
- Compounds with high oxidation states tend to be oxidising agents e.g
MnO4-- Compounds with low oxidation states are often reducing agents
e.g V2+ & Fe2+
four colour and symbol stages of Vanadium
VO2+ Oxidation state +5 ( a yellow
solution) VO2+ Oxidation state + 4 (a
blue solution) V3+ Oxidation state + 3 (a
green solution) V2+ Oxidation state + 2
(a violet solution) YOU BETTER GET
VANADIUM
what is used to reduce vanadium
Addition of zinc to the vanadium (V) in acidic solution will reduce the
vanadium down through each successive oxidation state, and the
colour would successively change from yellow to blue to green to
violet
what is used in testing for aldehydes
[Ag(NH3)2]+ is used in Tollen's reagent to distinguish between
aldehydes and ketones . Aldehydes reduce the silver in the Tollen's
reagent to silver
,why are dark colours of solutions difficult to measure
The purple colour of manganate can make it difficult to see the bottom
of meniscus in the burette.
what acid is used for manganate titrations
Only use dilute sulphuric acid for manganate titrations.
Insufficient volumes of sulphuric acid will mean the solution is not acidic
enough and MnO2 will be produced instead of Mn2+.
Using a weak acid like ethanoic acid would have the same effect as it
cannot supply the large amount of hydrogen ions needed (8H+).
It cannot be conc HCl as the Cl- ions would be oxidised to Cl2
, what is a heterogenous catalyst
in a different phase from the reactants
what is a homogenous catalyst
in the same phase as the reactants
what are standard conditions for heterogenous catalysts
Heterogeneous catalysts are usually solids whereas the reactants are
gaseous or in solution. The reaction occurs at the surface of the
catalyst.
how do heterogenous catalysts work
Adsorption of reactants at active sites on the surface may lead to catalytic
action. The active site is the place where the reactants adsorb on to the
surface of the catalyst. This can result in the bonds within the reactant
moleculesbecomingweaker,or themoleculesbeingheldin a more reactive
configuration. There will also be a higher concentration of reactants at the
solid surface so leading to a higher collision frequency.
VERIFIED ANSWERS ALREADY GRADED A+ 100%
GUARANTEED PASS LATEST UPDATE \University of
Glasgow
what is the equation which links the colour and frequency of the light
absorbed with the energy difference between the split d orbitals
E = hv.
v = frequency of light absorbed (unit s-1 or Hz) h= Planck's constant 6.63 ×
10-34 (J s)
E = energy difference between split orbitals (J)
how can you change colour of transition metals
Changing a ligand or changing the coordination number will alter the
energy split between the d- orbitals, changing E and hence change
the frequency of light absorbed
describe the method of spectroscopy
• Add an appropriate ligand to intensify colour •Make up solutions
of known concentration (dilution series)
• Measure absorption or transmission
• Plot graph of absorption vs concentration •Measure absorption of
unknown and compare
,general trend of variable oxidation states
- Relative stability of +2 state with respect to +3 state increases across the
period
- Compounds with high oxidation states tend to be oxidising agents e.g
MnO4-- Compounds with low oxidation states are often reducing agents
e.g V2+ & Fe2+
four colour and symbol stages of Vanadium
VO2+ Oxidation state +5 ( a yellow
solution) VO2+ Oxidation state + 4 (a
blue solution) V3+ Oxidation state + 3 (a
green solution) V2+ Oxidation state + 2
(a violet solution) YOU BETTER GET
VANADIUM
what is used to reduce vanadium
Addition of zinc to the vanadium (V) in acidic solution will reduce the
vanadium down through each successive oxidation state, and the
colour would successively change from yellow to blue to green to
violet
what is used in testing for aldehydes
[Ag(NH3)2]+ is used in Tollen's reagent to distinguish between
aldehydes and ketones . Aldehydes reduce the silver in the Tollen's
reagent to silver
,why are dark colours of solutions difficult to measure
The purple colour of manganate can make it difficult to see the bottom
of meniscus in the burette.
what acid is used for manganate titrations
Only use dilute sulphuric acid for manganate titrations.
Insufficient volumes of sulphuric acid will mean the solution is not acidic
enough and MnO2 will be produced instead of Mn2+.
Using a weak acid like ethanoic acid would have the same effect as it
cannot supply the large amount of hydrogen ions needed (8H+).
It cannot be conc HCl as the Cl- ions would be oxidised to Cl2
, what is a heterogenous catalyst
in a different phase from the reactants
what is a homogenous catalyst
in the same phase as the reactants
what are standard conditions for heterogenous catalysts
Heterogeneous catalysts are usually solids whereas the reactants are
gaseous or in solution. The reaction occurs at the surface of the
catalyst.
how do heterogenous catalysts work
Adsorption of reactants at active sites on the surface may lead to catalytic
action. The active site is the place where the reactants adsorb on to the
surface of the catalyst. This can result in the bonds within the reactant
moleculesbecomingweaker,or themoleculesbeingheldin a more reactive
configuration. There will also be a higher concentration of reactants at the
solid surface so leading to a higher collision frequency.
