Module 5: Electrochemistry And Transition Metals Flashcards
(158 cards)
1
Q
Redox equations
What is a redox equation made up of
A
Oxidisation half reaction and reduction half reaction
2
Q
Redox equations
How do you make a full redox equation
A
Combining a oxidation half equation with a reduction half equation
3
Q
Redox equations
How do you combine two half equations
A
Balancing electrons on each equation
4
Q
Redox equations
What are you allowed to add to balance a half equation
A
Electrons H+ ions and water
5
Q
Redox equations
How can you check a redox equation is balanced
A
Balanced charges
6
Q
Redox equations
Order to balance a half equation
A
Add electrons to balance oxidation sate of main element
Add water to balance oxygens
Add H+ ions to balance water
Check charges n balance
7
Q
Redox titrations
What are used and why in redox titrations
A
Transition elements change oxidation rate readily sp useful as oxidising and reducing agents so receive or give out electrons and change colour so easy to spot when reaction finished
8
Q
Redox titrations
Formula for manganate (VII) ions
A
MnO4^-
9
Q
Redox titrations
What oxidation state does manganese’s have in manganate (VII)
A
+7
10
Q
Redox titrations
What can manganate (VII) ions be reduced to
A
Mn^2+
11
Q
Redox titrations
What is the ration of Managanese (VII) to Fe2+
A
1:5
12
Q
Redox titrations
What is the ration of manganese (VII) to H2O2
A
2:5
13
Q
Redox titrations
What is the colour change with manganese (VII)
A
Purple to colourless
14
Q
Redox titrations
What type of agent is manganese (VII)
A
Oxidising
15
Q
Redox titrations
What kind of agent is dichromate
A
Oxidising
16
Q
Redox titrations
What is formula for dischromate (VI)
A
Cr2O7^2-
17
Q
Redox titrations
What oxidation state does chromium have in dichromate
A
+6
18
Q
Redox titrations
What can dichromate be reduced to
A
Cr3+
19
Q
Redox titrations
Ratio of dichromate to Zn
A
1:3
20
Q
Redox titrations
Colour change involving dichromate
A
Orange to green
21
Q
Redox titrations
What is important in redox titrations and why
A
May need acid in excess to ensure H+ ions
22
Q
Redox titrations
Titration procedures
A
First you measure out a quantity of the reducing agent, e.g. aqueous Fez+ ions, using a pipette, and put it in a conical flask.
You then add some dilute sulfuric acid to the flask
— this is an excess, so you don’t have to be too exact..
Now you gradually add the aqueous MnO, (the oxidising agent) to the reducing agent using a burette, swirling the conical flask as you do so.
4) You stop when the mixture in the flask just becomes tainted with the colour of the MnO,- (the end point) and record the volume of the oxidising agent added.
5) Run a few titrations and then calculate the mean volume of MnO,.
23
Q
Redox titrations
What can make the colour easier to spot
A
On white surface
24
Q
Electrochemistry
What can electrochemical cels be made from
A
Two different metals dipped in salt solutions of their own ions and connected by a wire
25
Electrochemistry
What reactions are happening in a electrochemical cell
Two one oxidation and one reduction
26
Electrochemistry
What happens in the half cell with oxising
Loses electrons more easily than other so releasing electrons to external circuits
27
Electrochemistry
What happens in the half cell with reduction
Electrons taken in from external circuit
28
Electrochemistry
What is salt bridge
Connects solutions
Made from filter paper soaked in KNO3 and allows ions to flow through and balance out charges
29
Electrochemistry
Where do electrons flow
In wire from most reactive metal to least
30
Electrochemistry
What does voltmeter measure
Shows voltage between two half cells which is the cell potential Ecell
31
Electrochemistry
How can you have a half cell with aqueous solution of two ions
Conversion occurs on surface of pt electrode
With ions in solutions
32
Electrochemistry
Why is a platinum electrode used
Inert and conducts electricity
33
Electrochemistry
How can have half cell using non metals or gas
Gas can be bubbled over a platinum electrode sitting in a solutions of aqueous ions
34
Electrochemistry
What is a standard electrode potential
Electromotive force when combined with a hydrogen half cell with standard conditions of 298K 101 kPa 1M in a complete circuit with a high resistance voltmeter
35
Electrochemistry
What does electrode potential tell you about a metal
How easily oxidise or reduces
36
Electrochemistrywhat does a more negative electrode potential tell you
Easily oxidised
37
Electrochemistry
What does a more Positve electrode potential
More easily reduced
38
Electrochemistry
What are important conventions when drawing cels
More negative potential on left
39
Electrochemistry
How to remember what reduced
Redcat+
40
Electrochemistry
Formula for Ecell
Emorepositive - Emorenegative
41
Electrochemistry
Which side is hydrogen half cell shown
Always on left
42
Electrochemistrywhat value does standard hydrogen electrode half cell have
0.00 v
43
Electrochemistry
How many dp are electrode potential given to
2
44
Electrochemistry
What kind of agent is more Positve Eo
Oxidising agent
45
Electrochemistry
Why are standard conditions used for standard electrode p[otentials
As reversible reactions change on temp changes position of equilibrium so electrode potential
46
Electrochemistry
Which way are equations written on electrochemical series
Reduction
47
Electrochemistry
When using electrode potentials to predict whether a reaction may happen why may it be wrong
If conditions not standard
If reactions kinetics are not favourable
48
Electrochemistry
Why may reaction kinetics not be favourabvkle
If rate of reaction too slow may not appear to happen
If activation energy too high
49
Electrochemistry
Why would non standard conditions change predictability of reactions
Eg if change of concentration position of equilibrium changes so electrode potential changes
50
Electrochemistry
What are electrochemical cells be used as
Commercial source of electrical energy
51
Electrochemistry]
What are the three important types of cell
Non rechargeable
Rechargeable
Fuel cells
52
Electrochemistry
What is an adavateg of cells
Portable source of electricity
53
Electrochemistry
Wjhat is a battery
More than one cells joined together
54
Electrochemistry
What happens in non rechargeable cells
Chemicals are used up over time and emf drops
Once one or more of chemical.s used up completely the cell is flat and the emf is 0 volts
55
Electrochemistry
What happens in rechargeable cells
Reactions are reversible
Reversed by applying an external; current and regenerate the chemicals
56
Electrochemistry
What kind of rechargebale cell is used in phon3s laptops cameras etc
Lithium ion
57
Electrochemistry
What are fuel cells
Have a continuous supply of the chemicals onto the cell and so neither run out nor need recharging but they do need to have a constant supply of the required chemicals
58
Electrochemistry
What is the most common fuel cell
Hydrogen oxygen fuel cell
59
Electrochemistry
What conditions can hydrogen oxygen fuel cells be run in
Alkaline or acidic
60
Electrochemistry
What is true for both acid and alkaline hydrogen oxygen fuel cells
Overall equation and overlll emf is the same
61
Electrochemistry
What is the iover emf and equation for hydrogen oxygen fuel cells
2 H2 + O2 —> 2 H2O
+1.23v
62
Electrochemistry
Benefit and risks of using non rechargeable cells
+cheap
-waste issues
63
Electrochemistry
Benefit and risks of re chargeable cells
+less waste
+cheaper in long run
+lower environmental impact
- some waste issues at end of useful life
-lithium ions can lead to fires
64
Electrochemistry
Benefits and silk of hydrogen fuel cells
+only waste product is water
+ don’t need recharging
+vcery efficient
-need constant suppl,y of fuels
-hydrogen is flammable and explosive
-hydrogen made using fossil fuels
-high cost of fossil fuels
65
66
Transitions elements
What are d block elements
Highest energy electron in d orbital
67
Transitions elements
What are transition elements
Elements that can form atleast one ion with a partially filled d subshell
68
Transitions elements
Examp,e of two elements that are d block elements but not transition elements
Sc
Zn
69
Transitions elements
Why is sc a d bloc element but not a transition elemnt
Highest energy electron is in a d subshell [Ar]4s2 3d1 but only forms Sc3+ ion [Ar] so has no d subshell
70
Transitions elements
Why is Zn a d block element but not a transition element
Highest energy electron in d subshell [Ar] 4s2 3d10 but only forms a Zn2+ ion [Ar]3d10 which is full
71
Transitions elements
What are the three typical properties of transition elements
Catalysts
Form coloured ions
Have variable oxidation states
72
Transitions elements
Examples of transition elements as catalysts
Cu2+ in reaction between Zn and acid
Fe in haber process
MnO2 in decomposition of H2O2
73
Transitions elements
What are ligands
Atom or ion with a lone pair that forms coordinate bond to metal
74
Transitions elements
What is a complex
Metal ion with ligand coordinate lay bonded to it
75
Transitions elements
What is coordination number
Number of coordinate bonds from ligands to metal ions
76
Transitions elements
How do you write formula for complex
Metal then ligands in square bracket with overall charge
77
Transitions elements
What shapes can they form
Same as organic
78
Transitions elements
How are coordination bonds shown
Arrow towards metal
79
Transitions elements
What does monodentate mean
Ligands can only form one coordinate bond
80
Transitions elements
What does bidentate mean
Ligands can form two coordinate bonds
81
82
Complexes
What are common monodentate
H2O NH3 Cl-
83
Complexes
What do ligands have to have
Lone pair of electrons
84
Complexes
What shapes can compl;exes form
Linear
Square planar
Tetrahedral
Octahedral
85
Complexes
What is coordination number of linear
2
86
Complexes
When does linear occur
With Ag+ complex
87
Complexes
What is tollens reagent
[Ag(NH3)2]+
88
Complexes
What is bond angle of linear
180
89
Complexes
What is coordination number of square planar
4
90
Complexes
When does square planar occur
Pt2+ and Ni2+ complex
91
Complexes
Bond angle in square planar
90
92
Complexes
Coordination number in tetrahedral
4
93
Complexes
Bond angle in tetrahedral
109.5
94
Complexes
When does tetrahedral occur
With larger ligands eg cl- (too big for 6 to fit)
95
Complexes
Coordination number for octahedral
6
96
Complexes
Bond angle for octahedral
90
97
Complexes
When does octahedral occur
Most complexes with small ligands eg h20 or nh3
98
Redox titrations
Why are transition elements used
Good At changing oxidation state and acting as reducing or oxidising agents
Change colour so can observe endpoint
99
Iodine thiosulphate titrations
What do these find the concentration of
Oxidising agents
100
Iodine thiosulphate titrations
What is stage 1
Use sample of oxidising agents to oxidise as much iodide as possible
101
102
Iodine thiosulphate titrations
Methods for stage 1
Measure out certain volume of oxidising agents eg 25cm3
Add to excess of KI solutions
Oxidising agent oxidises all of iodide to iodine
103
Iodine thiosulphate titrations
Example or reaction of iodide with iodate
IO3^- + 5I^- + 6H^+ —> 3I2 + 3H2O
104
Iodine thiosulphate titrations
What is stage 2
Find out how many mole iodine have been produced
105
Iodine thiosulphate titrations
Method for stage 2
Titrate resulting solitons with sodium thiosulphate
106
Iodine thiosulphate titrations
Equation for thiosulphate and iodine
I2 + 2S2O3^2- —> 2I^- + S4O6^2-
107
Iodine thiosulphate titrations
How is end point clearly seen
Close to end point starch added
108
Iodine thiosulphate titrations
What is colour change with starch
Blue black to colourless
109
Transition metals
Why do they show varied oxidation states
Because the energy levels of the 4s and 3d subshells are very close to one another so different numbers of electrons can be gained or lost using fairly similar amounts of energy
110
Transition metals
Why are they good catalysts
Change oxidation states by gaining or losing electrons in orbital so can transfer electrons to speed up reactions
Also good at adsorbing substances onto their surfaces to lower the ea
111
Transition metals
What is CuSO4 a good catalyst for
Reaction of zinc with acids
Zn + H2SO4 —CuSO4–> ZnSO4 + H2
112
Transition metals
What os MnO2 a good catalyst for and equation
Decompositions of hydrogen peroxide
H2O2 —MnO2–> 2H2O + O2
113
Transition metals
Why are catalysts good for environments and industry
Allow reactions to happen faster and at lower temperatures amnd pressures reducing energy usage
114
Transition metals
What is limitation for using transition metals as catalysts
Can pose health risks as many are toxic
115
Transition metals
What happens when you mix aq solutions of transition ion with aq NaOH or aq NH3
Coloured hydroxide precipitate
116
Transition metals
What form do transition elemnts take in aq solutions
[M(H2O)6]^n+
117
Transition metals
Copper ll and NaOH
Cu^2+ (aq) + 2OH^- —> Cu(OH)2 (s)
118
Transition metals
Copper ll and drop wise ammonia
[Cu(H2O)6]^2+ (aq) + 2NH3 —> [Cu(OH)2(H2O)4] (s) + 2NH4^+
119
Transition metals
Copper ll and excess NH3
[Cu(OH)2(H2O)4](s) + 4NH3 (aq) —> [Cu(NH3)4(H2O)2]^2+(aq) +2H2O
120
Transition metals
Iron ll with NaOH or NH3
Fe^2+ + 2OH^- (aq) —> Fe(OH)2(s)
121
Transition metals
Iron lll with NaOH
Fe^3+(aq) + 3OH^-(aq) —> Fe(OH)3(s)
122
Transition metals
Manganesell and NaOH
Mn^2+ (aq) + 2OH-(aq) —> Mn(OH)2(s)
123
Transition metals
Chromoium lll with dropwise NaOH or nh3
Cr^3+(aq) + 3OH^-(aq) —> Cr(OH)3(s)
124
Transition metals
Chromium lll with excess NaOH
Cr^3+ + 6OH^- (aq) —> [Cr(OH)6]^3-
125
Transition metals
Chromium lll excess NH3
Cr^3+(aq) + 6NH3(aq) —> [Cr(NH3)6]^3+ (aq)
126
Transition metals
What type of isomerism
Optical
Cis trans
127
Transition metals
When does optical isomerism occur
Octahedral complex with bidentate ligands
128
Transition metals
How do you draw optical
Draw one then mirror image
129
Transition metals
When can cis trans isomerism occur
In octahedral or square planner when two types of ligands and a pair of one type
130
Transition metals
When are they cis
When Pair of same ligands are next to each other
131
Transition metals
When are transi
When pair of same ligands are opposite
132
Transition metals
What is cis platin
Complex of platinum ll with two chloride ions and two ammonia moleucles in square planar shape
133
Transition metals
What is cis platin used as
Anticancer drug
134
Transition metals
How does cis platin work
Two chloride ligands are easy to replace so cis platin loses them and bonds to N atom on the dna moleucles inside cancerous cell instead
Block on cancerous cell prevent from reproducing by division
135
Transition metals
What is down side to cis platin
Also prevent normal cells from reproducing including blood with can suppress the immune system and increase chance of infection
May also cause damage to kidneys
136
Transition metals
What is ligand substitution
When one ligand is swapped for another
137
Transition metals
What happens if ligands are similar size
Coordination number and shape don’t change
138
Transition metals
What happens if ligands are different sizes
Change of coordination number and shape
Eg h20 and Cl-
139
Transition metals
What else can happen in ligand substituent
Only partial substitution so not all ligand swapped
140
Transition metals
How is Fe^2+ oxidised to Fe^3+
By acidified potassium manganate
141
Transition metals
Equation for manganate Vll reduced
MnO4^- + 8H^+ + 5e^- —> Mn^2+ + 4H2O
142
Transition metals
Equation for iron ll oxidised
Fe^2+ —> Fe^3+ + e^-
143
Transition metals
Overall equation mangant and iron
MnO4^- + 8H^+ + 5Fe^2+ —> Mn^2+ + 4H2O + 5Fe^3+
144
Transition metal
How is fe3+ reduced to fe2+
Iodide ions
145
Transition metals
Iodide oxidised
2I^- —> I2 + 2e^-
146
Transition metals
Iron lll reduced
Fe^3+ + e^- —> Fe^2+
147
Transition metals
How is Cr3+ reduced to CrO4^2-
Warming with H2O2 in alkaline conditons
148
Transition metals
Oxygen reduced in hydrogen peroxide
H2O2 + 2e^- —> 2OH^-
149
Transition metals
Chromium lll oxidised
2Cr(OH)6^3- + 4OH^- —> 2CrO4^2- + 8H2O + 6e^-
150
Transition metals
Crpomium lll and hydrogen peroxide
3H2O2 + 2Cr(OH)6^2- —> 2OH^- + 2CrO4^2- + 8H2O
151
Transition metals
Equation for sulfuric acid added to chromate VI
2CrO4^2- + 2H^+ —> Cr2O7^2- + H2O
152
Transition metals
How is Cr2O7^2- reduced to Cr^3+
Acidified zinc
153
Transition metals
Zinc oxidised
Zn __> Zn^2+ + 2e^-
154
Transition metals
Dichromate vll reduced
Cr2O7^2- + 14H^+ + 6e^- —> 2Cr^3+ +7H2O
155
Transition metals
Dichromate VII and Zn
Cr2O7^2- +14H^+ + 3Zn —> 2Cr^3+ + 7H2O + 3Zn^2+
156
Transition metals
Transition metals
How is cu ll reduced and equation
By iodide ions
2Cu^2+ + 4I^- —> 2CuI + I2
157
Transition metals
How is Cu l disproportionated and equation
Unstable so spontaneous
2Cu+ —> Cu^2+ + Cu
158
