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Alevel Chemistry OCR A > Module 5: Electrochemistry And Transition Metals > Flashcards

Module 5: Electrochemistry And Transition Metals Flashcards

1
Q

Redox equations
What is a redox equation made up of

A

Oxidisation half reaction and reduction half reaction

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2
Q

Redox equations
How do you make a full redox equation

A

Combining a oxidation half equation with a reduction half equation

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3
Q

Redox equations
How do you combine two half equations

A

Balancing electrons on each equation

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4
Q

Redox equations
What are you allowed to add to balance a half equation

A

Electrons H+ ions and water

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5
Q

Redox equations
How can you check a redox equation is balanced

A

Balanced charges

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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

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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

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8
Q

Redox titrations
Formula for manganate (VII) ions

A

MnO4^-

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9
Q

Redox titrations
What oxidation state does manganese’s have in manganate (VII)

A

+7

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10
Q

Redox titrations
What can manganate (VII) ions be reduced to

A

Mn^2+

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11
Q

Redox titrations
What is the ration of Managanese (VII) to Fe2+

A

1:5

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12
Q

Redox titrations
What is the ration of manganese (VII) to H2O2

A

2:5

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13
Q

Redox titrations
What is the colour change with manganese (VII)

A

Purple to colourless

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14
Q

Redox titrations
What type of agent is manganese (VII)

A

Oxidising

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15
Q

Redox titrations
What kind of agent is dichromate

A

Oxidising

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16
Q

Redox titrations
What is formula for dischromate (VI)

A

Cr2O7^2-

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17
Q

Redox titrations
What oxidation state does chromium have in dichromate

A

+6

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18
Q

Redox titrations
What can dichromate be reduced to

A

Cr3+

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19
Q

Redox titrations
Ratio of dichromate to Zn

A

1:3

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20
Q

Redox titrations
Colour change involving dichromate

A

Orange to green

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21
Q

Redox titrations
What is important in redox titrations and why

A

May need acid in excess to ensure H+ ions

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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,.

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23
Q

Redox titrations
What can make the colour easier to spot

A

On white surface

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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

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25
Q

Electrochemistry
What reactions are happening in a electrochemical cell

A

Two one oxidation and one reduction

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26
Q

Electrochemistry
What happens in the half cell with oxising

A

Loses electrons more easily than other so releasing electrons to external circuits

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27
Q

Electrochemistry
What happens in the half cell with reduction

A

Electrons taken in from external circuit

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28
Q

Electrochemistry
What is salt bridge

A

Connects solutions
Made from filter paper soaked in KNO3 and allows ions to flow through and balance out charges

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29
Q

Electrochemistry
Where do electrons flow

A

In wire from most reactive metal to least

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30
Q

Electrochemistry
What does voltmeter measure

A

Shows voltage between two half cells which is the cell potential Ecell

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31
Q

Electrochemistry
How can you have a half cell with aqueous solution of two ions

A

Conversion occurs on surface of pt electrode
With ions in solutions

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32
Q

Electrochemistry
Why is a platinum electrode used

A

Inert and conducts electricity

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33
Q

Electrochemistry
How can have half cell using non metals or gas

A

Gas can be bubbled over a platinum electrode sitting in a solutions of aqueous ions

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34
Q

Electrochemistry
What is a standard electrode potential

A

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

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35
Q

Electrochemistry
What does electrode potential tell you about a metal

A

How easily oxidise or reduces

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36
Q

Electrochemistrywhat does a more negative electrode potential tell you

A

Easily oxidised

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37
Q

Electrochemistry
What does a more Positve electrode potential

A

More easily reduced

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38
Q

Electrochemistry
What are important conventions when drawing cels

A

More negative potential on left

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39
Q

Electrochemistry
How to remember what reduced

A

Redcat+

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40
Q

Electrochemistry
Formula for Ecell

A

Emorepositive - Emorenegative

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41
Q

Electrochemistry
Which side is hydrogen half cell shown

A

Always on left

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42
Q

Electrochemistrywhat value does standard hydrogen electrode half cell have

A

0.00 v

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43
Q

Electrochemistry
How many dp are electrode potential given to

A

2

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44
Q

Electrochemistry
What kind of agent is more Positve Eo

A

Oxidising agent

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45
Q

Electrochemistry
Why are standard conditions used for standard electrode p[otentials

A

As reversible reactions change on temp changes position of equilibrium so electrode potential

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46
Q

Electrochemistry
Which way are equations written on electrochemical series

A

Reduction

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47
Q

Electrochemistry
When using electrode potentials to predict whether a reaction may happen why may it be wrong

A

If conditions not standard
If reactions kinetics are not favourable

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48
Q

Electrochemistry
Why may reaction kinetics not be favourabvkle

A

If rate of reaction too slow may not appear to happen
If activation energy too high

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49
Q

Electrochemistry
Why would non standard conditions change predictability of reactions

A

Eg if change of concentration position of equilibrium changes so electrode potential changes

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50
Q

Electrochemistry
What are electrochemical cells be used as

A

Commercial source of electrical energy

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51
Q

Electrochemistry]
What are the three important types of cell

A

Non rechargeable
Rechargeable
Fuel cells

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52
Q

Electrochemistry
What is an adavateg of cells

A

Portable source of electricity

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53
Q

Electrochemistry
Wjhat is a battery

A

More than one cells joined together

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54
Q

Electrochemistry
What happens in non rechargeable cells

A

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

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55
Q

Electrochemistry
What happens in rechargeable cells

A

Reactions are reversible
Reversed by applying an external; current and regenerate the chemicals

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56
Q

Electrochemistry
What kind of rechargebale cell is used in phon3s laptops cameras etc

A

Lithium ion

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57
Q

Electrochemistry
What are fuel cells

A

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

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58
Q

Electrochemistry
What is the most common fuel cell

A

Hydrogen oxygen fuel cell

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59
Q

Electrochemistry
What conditions can hydrogen oxygen fuel cells be run in

A

Alkaline or acidic

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60
Q

Electrochemistry
What is true for both acid and alkaline hydrogen oxygen fuel cells

A

Overall equation and overlll emf is the same

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61
Q

Electrochemistry
What is the iover emf and equation for hydrogen oxygen fuel cells

A

2 H2 + O2 —> 2 H2O
+1.23v

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62
Q

Electrochemistry
Benefit and risks of using non rechargeable cells

A

+cheap
-waste issues

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63
Q

Electrochemistry
Benefit and risks of re chargeable cells

A

+less waste
+cheaper in long run
+lower environmental impact
- some waste issues at end of useful life
-lithium ions can lead to fires

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64
Q

Electrochemistry
Benefits and silk of hydrogen fuel cells

A

+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

66
Q

Transitions elements
What are d block elements

A

Highest energy electron in d orbital

67
Q

Transitions elements
What are transition elements

A

Elements that can form atleast one ion with a partially filled d subshell

68
Q

Transitions elements
Examp,e of two elements that are d block elements but not transition elements

69
Q

Transitions elements
Why is sc a d bloc element but not a transition elemnt

A

Highest energy electron is in a d subshell [Ar]4s2 3d1 but only forms Sc3+ ion [Ar] so has no d subshell

70
Q

Transitions elements
Why is Zn a d block element but not a transition element

A

Highest energy electron in d subshell [Ar] 4s2 3d10 but only forms a Zn2+ ion [Ar]3d10 which is full

71
Q

Transitions elements
What are the three typical properties of transition elements

A

Catalysts
Form coloured ions
Have variable oxidation states

72
Q

Transitions elements
Examples of transition elements as catalysts

A

Cu2+ in reaction between Zn and acid
Fe in haber process
MnO2 in decomposition of H2O2

73
Q

Transitions elements
What are ligands

A

Atom or ion with a lone pair that forms coordinate bond to metal

74
Q

Transitions elements
What is a complex

A

Metal ion with ligand coordinate lay bonded to it

75
Q

Transitions elements
What is coordination number

A

Number of coordinate bonds from ligands to metal ions

76
Q

Transitions elements
How do you write formula for complex

A

Metal then ligands in square bracket with overall charge

77
Q

Transitions elements
What shapes can they form

A

Same as organic

78
Q

Transitions elements
How are coordination bonds shown

A

Arrow towards metal

79
Q

Transitions elements
What does monodentate mean

A

Ligands can only form one coordinate bond

80
Q

Transitions elements
What does bidentate mean

A

Ligands can form two coordinate bonds

82
Q

Complexes
What are common monodentate

A

H2O NH3 Cl-

83
Q

Complexes
What do ligands have to have

A

Lone pair of electrons

84
Q

Complexes
What shapes can compl;exes form

A

Linear
Square planar
Tetrahedral
Octahedral

85
Q

Complexes
What is coordination number of linear

86
Q

Complexes
When does linear occur

A

With Ag+ complex

87
Q

Complexes
What is tollens reagent

A

[Ag(NH3)2]+

88
Q

Complexes
What is bond angle of linear

89
Q

Complexes
What is coordination number of square planar

90
Q

Complexes
When does square planar occur

A

Pt2+ and Ni2+ complex

91
Q

Complexes
Bond angle in square planar

92
Q

Complexes
Coordination number in tetrahedral

93
Q

Complexes
Bond angle in tetrahedral

94
Q

Complexes
When does tetrahedral occur

A

With larger ligands eg cl- (too big for 6 to fit)

95
Q

Complexes
Coordination number for octahedral

96
Q

Complexes
Bond angle for octahedral

97
Q

Complexes
When does octahedral occur

A

Most complexes with small ligands eg h20 or nh3

98
Q

Redox titrations
Why are transition elements used

A

Good At changing oxidation state and acting as reducing or oxidising agents
Change colour so can observe endpoint

99
Q

Iodine thiosulphate titrations
What do these find the concentration of

A

Oxidising agents

100
Q

Iodine thiosulphate titrations
What is stage 1

A

Use sample of oxidising agents to oxidise as much iodide as possible

102
Q

Iodine thiosulphate titrations
Methods for stage 1

A

Measure out certain volume of oxidising agents eg 25cm3
Add to excess of KI solutions
Oxidising agent oxidises all of iodide to iodine

103
Q

Iodine thiosulphate titrations
Example or reaction of iodide with iodate

A

IO3^- + 5I^- + 6H^+ —> 3I2 + 3H2O

104
Q

Iodine thiosulphate titrations
What is stage 2

A

Find out how many mole iodine have been produced

105
Q

Iodine thiosulphate titrations
Method for stage 2

A

Titrate resulting solitons with sodium thiosulphate

106
Q

Iodine thiosulphate titrations
Equation for thiosulphate and iodine

A

I2 + 2S2O3^2- —> 2I^- + S4O6^2-

107
Q

Iodine thiosulphate titrations
How is end point clearly seen

A

Close to end point starch added

108
Q

Iodine thiosulphate titrations
What is colour change with starch

A

Blue black to colourless

109
Q

Transition metals
Why do they show varied oxidation states

A

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
Q

Transition metals
Why are they good catalysts

A

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
Q

Transition metals
What is CuSO4 a good catalyst for

A

Reaction of zinc with acids
Zn + H2SO4 —CuSO4–> ZnSO4 + H2

112
Q

Transition metals
What os MnO2 a good catalyst for and equation

A

Decompositions of hydrogen peroxide
H2O2 —MnO2–> 2H2O + O2

113
Q

Transition metals
Why are catalysts good for environments and industry

A

Allow reactions to happen faster and at lower temperatures amnd pressures reducing energy usage

114
Q

Transition metals
What is limitation for using transition metals as catalysts

A

Can pose health risks as many are toxic

115
Q

Transition metals
What happens when you mix aq solutions of transition ion with aq NaOH or aq NH3

A

Coloured hydroxide precipitate

116
Q

Transition metals
What form do transition elemnts take in aq solutions

A

[M(H2O)6]^n+

117
Q

Transition metals
Copper ll and NaOH

A

Cu^2+ (aq) + 2OH^- —> Cu(OH)2 (s)

118
Q

Transition metals
Copper ll and drop wise ammonia

A

[Cu(H2O)6]^2+ (aq) + 2NH3 —> [Cu(OH)2(H2O)4] (s) + 2NH4^+

119
Q

Transition metals
Copper ll and excess NH3

A

Cu(OH)2(H2O)4 + 4NH3 (aq) —> [Cu(NH3)4(H2O)2]^2+(aq) +2H2O

120
Q

Transition metals
Iron ll with NaOH or NH3

A

Fe^2+ + 2OH^- (aq) —> Fe(OH)2(s)

121
Q

Transition metals
Iron lll with NaOH

A

Fe^3+(aq) + 3OH^-(aq) —> Fe(OH)3(s)

122
Q

Transition metals
Manganesell and NaOH

A

Mn^2+ (aq) + 2OH-(aq) —> Mn(OH)2(s)

123
Q

Transition metals
Chromoium lll with dropwise NaOH or nh3

A

Cr^3+(aq) + 3OH^-(aq) —> Cr(OH)3(s)

124
Q

Transition metals
Chromium lll with excess NaOH

A

Cr^3+ + 6OH^- (aq) —> [Cr(OH)6]^3-

125
Q

Transition metals
Chromium lll excess NH3

A

Cr^3+(aq) + 6NH3(aq) —> [Cr(NH3)6]^3+ (aq)

126
Q

Transition metals
What type of isomerism

A

Optical
Cis trans

127
Q

Transition metals
When does optical isomerism occur

A

Octahedral complex with bidentate ligands

128
Q

Transition metals
How do you draw optical

A

Draw one then mirror image

129
Q

Transition metals
When can cis trans isomerism occur

A

In octahedral or square planner when two types of ligands and a pair of one type

130
Q

Transition metals
When are they cis

A

When Pair of same ligands are next to each other

131
Q

Transition metals
When are transi

A

When pair of same ligands are opposite

132
Q

Transition metals
What is cis platin

A

Complex of platinum ll with two chloride ions and two ammonia moleucles in square planar shape

133
Q

Transition metals
What is cis platin used as

A

Anticancer drug

134
Q

Transition metals
How does cis platin work

A

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
Q

Transition metals
What is down side to cis platin

A

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
Q

Transition metals
What is ligand substitution

A

When one ligand is swapped for another

137
Q

Transition metals
What happens if ligands are similar size

A

Coordination number and shape don’t change

138
Q

Transition metals
What happens if ligands are different sizes

A

Change of coordination number and shape
Eg h20 and Cl-

139
Q

Transition metals
What else can happen in ligand substituent

A

Only partial substitution so not all ligand swapped

140
Q

Transition metals
How is Fe^2+ oxidised to Fe^3+

A

By acidified potassium manganate

141
Q

Transition metals
Equation for manganate Vll reduced

A

MnO4^- + 8H^+ + 5e^- —> Mn^2+ + 4H2O

142
Q

Transition metals
Equation for iron ll oxidised

A

Fe^2+ —> Fe^3+ + e^-

143
Q

Transition metals
Overall equation mangant and iron

A

MnO4^- + 8H^+ + 5Fe^2+ —> Mn^2+ + 4H2O + 5Fe^3+

144
Q

Transition metal
How is fe3+ reduced to fe2+

A

Iodide ions

145
Q

Transition metals
Iodide oxidised

A

2I^- —> I2 + 2e^-

146
Q

Transition metals
Iron lll reduced

A

Fe^3+ + e^- —> Fe^2+

147
Q

Transition metals
How is Cr3+ reduced to CrO4^2-

A

Warming with H2O2 in alkaline conditons

148
Q

Transition metals
Oxygen reduced in hydrogen peroxide

A

H2O2 + 2e^- —> 2OH^-

149
Q

Transition metals
Chromium lll oxidised

A

2Cr(OH)6^3- + 4OH^- —> 2CrO4^2- + 8H2O + 6e^-

150
Q

Transition metals
Crpomium lll and hydrogen peroxide

A

3H2O2 + 2Cr(OH)6^2- —> 2OH^- + 2CrO4^2- + 8H2O

151
Q

Transition metals
Equation for sulfuric acid added to chromate VI

A

2CrO4^2- + 2H^+ —> Cr2O7^2- + H2O

152
Q

Transition metals
How is Cr2O7^2- reduced to Cr^3+

A

Acidified zinc

153
Q

Transition metals
Zinc oxidised

A

Zn __> Zn^2+ + 2e^-

154
Q

Transition metals
Dichromate vll reduced

A

Cr2O7^2- + 14H^+ + 6e^- —> 2Cr^3+ +7H2O

155
Q

Transition metals
Dichromate VII and Zn

A

Cr2O7^2- +14H^+ + 3Zn —> 2Cr^3+ + 7H2O + 3Zn^2+

156
Q

Transition metals

Transition metals
How is cu ll reduced and equation

A

By iodide ions
2Cu^2+ + 4I^- —> 2CuI + I2

157
Q

Transition metals
How is Cu l disproportionated and equation

A

Unstable so spontaneous
2Cu+ —> Cu^2+ + Cu

Alevel Chemistry OCR A (18 decks)

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