Module 5 Flashcards
(274 cards)
1
Q
What is rate of reaction? (1 mark)
A
Quantity reacted or produced/ change in time
2
Q
What is the shorthand for concentration of A? (1 mark)
A
[A]
Must be square brackets
3
Q
What is rate of reaction proportional to? (1 mark)
A
[A]^n
n= order of reaction
‘Concentration of a reactant to the power of n’
4
Q
What is the order of the reaction if a reactant has no effect on the rate? (1 mark)
A
0
5
Q
What does a reaction order of 1 mean, give an example? (2 marks)
A
The rate depends on it’s concentration raised to the power of 1.
So if the concentration of A is doubled, the rate of reaction increases by a factor of 2^1
6
Q
What does a reaction order of 2 mean, give an example? (2 marks)
A
The rate depends on it’s concentration raised to the power of 2.
So if the concentration of A is doubled, the rate of reaction increases by a factor of 2^2
7
Q
What is the overall order? (1 mark)
A
The overall effect of the concentration of all the reactants on the rate of reaction.
8
Q
How do you work out overall order? (1 mark)
A
The sum of all orders with respect to each reactant.
9
Q
What is an equation for rate which contains the rate constant and order of reaction? (2 marks)
A
rate= k x [A]^m x [B]^n
k- rate constant
m- order with respect to A
n- order with respect to B
10
Q
How is the data for a concentration-time graph collected? (3 marks)
A
Continuous monitoring over the course of a reaction.
By collecting gas formed, mass loss, or colour change (using a colorimeter).
11
Q
Describe how to analyse using colorimetry. (6 marks)
A
Prepare standard solutions of coloured chemical.
Use a filter with complementary colour.
Zero the colorimeter with water.
Measure the absorbance of the standard solutions and plot a calibration curve.
Conduct reaction and take absorbance readings at intervals.
Use the calibration curve to calculate the concentration of the chemical at the absorbance reading.
Plot a concentration-time graph.
12
Q
What does the shape of a concentration-time graph tell you? (1 mark)
A
the order of the reaction (for 1st and 0th)
13
Q
What does the concentration-time graph of a zero-order reaction look like? (2 marks)
A
Straight line
Negative gradient
14
Q
In a zero-order reaction, what does the gradient of the concentration-time graph tell you? (1 mark)
A
The rate constant (k).
15
Q
What does the concentration-time graph of a first-order reaction look like? (3 marks)
A
Downward curve
Decreasing concentration
Half life is constant (the time the concentration takes to halve)
16
Q
What does the concentration-time graph of a second-order reaction look like? (2 marks)
A
Downward curve
Steeper at the start and tails off more slowly.
17
Q
How do you calculate k from rate of reaction (for first order reaction)? (3 marks)
A
Choose a random concentration, on a concentration-time graph, and draw a tangent to find rate at that concentration.
Substitute this value into the rate equation.
18
Q
How do you calculate k from half life (for a first order reaction)?
A
k= ln2/ half life
19
Q
What does the rate-concentration graph look like for a zero order reaction? (1 mark)
A
Horizontal straight line
20
Q
What does the rate-concentration graph look like for a first order reaction? (1 mark)
A
Straight line through origin.
21
Q
What does the rate-concentration graph look like for a second order reaction? (2 mark)
A
Upward curve with increasing gradient.
22
Q
Where is k on a rate-concentration graph for a zero order reaction, why? (2 marks)
A
The y intercept
Because the rate equation is:
Rate= k[A]^0
So Rate= k
23
Q
Where is k on a rate-concentration graph for a first order reaction, why? (2 marks)
A
The gradient of the line
Because rate equation is:
Rate= k[A]^1
So Rate= k[A]
24
Q
How do you find k from a rate-concentration graph for a second order reaction? (3 marks)
A
Plot a second graph (rate against concentration^2)
K is the gradient of the straight line.
25
Describe the clock reaction. (3 marks)
If there is no significant change in rate, then record the time until visual change.
In this case, the initial rate is inversely proportional to the time.
26
What do iodine clocks rely on? (2 marks)
The formation of iodine (the colour would change from orange to black).
27
How accurate are clock reactions, over time?
It measures the average rate of change in reactant over time, so the less of a reaction taken place, the more accurate it is.
28
What is the slowest step in a reaction mechanism called? (1 mark)
The rate-determining step
29
What does the rate equation contain? (1 mark)
Only the reactants from the rate determining step.
E.g. EF + F —> G
rate= k[E][F]^2
30
What happens to the rate constant as temperature increases? (1 mark)
The rate constant increases.
31
Why does the rate constant increase when temperature increases? (5 marks)
It shifts the Boltzmann distribution to the right, so more particles exceed the activation energy.
It also causes particles to move faster and collide more frequently at the right orientation.
However, the number of particles exceeding activation energy has much more of an effect than frequency collisions.
32
What does the exponential factor, in the Arrhenius equation, represent? (1 mark)
The proportion of molecules/particles that exceed Ea.
33
What does the frequency factor, in the Arrhenius equation, take into account? (2 marks)
The frequency of collisions
with the correct orientation.
34
The Arrhenius equation is shown below:
k= Ae^(-Ea/RT)
What is the logarithmic form of this equation, pair each term up with a term form the equation y= mx + c?
lnk = -Ea/RT • 1/T + lnA
y = m • x + c
35
If you plot a graph of lnk against 1/T, what is the gradient (according to the Arrhenius equation)?
-Ea/R
36
If you plot a graph of lnk against 1/T, what is the y-intercept (according to the Arrhenius equation)?
lnA
37
What are the two main types of equilibria? (2 marks)
Homogeneous
Heterogeneous
38
What is homogeneous equilibrium? (2 marks)
Species all the same state.
Everything is included in the equation for Kc
39
What is heterogeneous equilibrium? (2 marks)
Species have different states.
Solids and liquids are not included in equation for Kc.
40
Why are solids and liquids not included in a heterogenous Kc equation? (1 mark)
The concentration of solids and liquids are essentially constant.
41
What do the values in the square brackets in the Kc equation represent? (2 marks)
**Concentration**of species
At **equilibrium**
42
What environmental factor affects K? (1 mark)
Temperature
43
What happens to K when temperature increases, in an exothermic reaction? (1 mark)
Decreases
44
What happens to K when temperature increases, in an endothermic reaction? (1 mark)
Increases
45
Describe the effect of increasing the pressure on Kc for a reaction with less moles on the right. (3 marks)
An increase in pressure causes an increase in concentration.
Terms on the bottom of the Kc are more than on the top.
Therefore, the top if the expression increases and the bottom decreases until (the original) Kc is reached, and equilibrium restored.
46
Describe what happens to Kp when the temperature is increased, in an exothermic reaction. (5 marks)
The system is no longer in equilibrium.
The expression is now greater than Kp.
Therefore, the partial pressure of the products must decrease and the partial pressure of the reactants must increase.
Until a new equilibrium is reached, with a new Kp.
Which is lower than the original.
47
Describe what happens to Kp when the temperature is increased, in an endothermic reaction. (5 marks)
The system is no longer in equilibrium.
The expression is now less than Kp.
Therefore, the partial pressure of the products must increase and the partial pressure of the reactants must decrease.
Until a new equilibrium is reached, with a new Kp.
Which is greater than the original.
48
What is the equation for mole fraction? (2 marks)
x(A) = no. of moles of A/ total no. of moles in gas mixture
49
What is the equation for partial pressure? (2 marks)
Partial pressure = mole fraction of A x total pressure
50
What is the relationship between partial pressures and total pressure? (1 mark)
Sum of partial pressures = total pressure
51
What state does the expression for Kp only contain? (1 mark)
Gas
52
What are the three acceptable units for partial pressure? (3 marks)
kPa
Pa
atm
53
What is an acid, according to Brønsted-Lowry? (1 mark)
An acids is a proton donor.
54
What is a base, according to Brønsted-Lowry? (1 mark)
A base is a proton acceptor.
55
What is a conjugate acid-pair, give an example? (2 marks)
A conjugate acid-pair is two species that can be interconverted by transfer of a proton (H+ ion).
56
What is a monobasic acid, give an example? (2 marks)
An acid which can donate one proton.
HCl, CH3COOH, HNO3
57
What is a dibasic acid, give an example? (2 marks)
An acid which can donate 2 protons.
H2SO4, H2CO3
58
What is a tribasic acid, give an example? (2 marks)
An acid which can donate 3 protons.
H3BO3, H3PO4
59
What are two ways a neutralisation equation can be written? (2 marks)
H3O+ + OH- —> 2H2O
and
H+ + OH- —> H2O
60
Who came up with the pH scale? (1 mark)
Søren Sørensen
61
What is the pH scale? (1 mark)
Numerical scale for measuring hydrogen ion concentrations.
62
What are the pH values of acidic, alkaline, and neutral solutions? (3 marks)
<7 is acidic
7< is alkaline
=7 is neutral
63
What is the equation that represents the relationship between pH and the concentration of H+ ions? (2 marks)
pH= -log[H+ (aq)]
or 10^-pH = [H+ (aq)]
64
What is the concentration of H+ ions in a strong acid with one hydrogen, and why? (2 marks)
The same as the concentration of the acid, because the acid completely disassociates.
65
Dilution changes the pH of a solution, true or false? (1 mark)
True
66
What is a chemical called when it can act as an acid or a base? (1 mark)
Amphoteric
67
Does water act as an acid or base when reacting with strong acids? (1 mark)
Base
68
Does water act as an acid or base when reacting with weak acids? (1 mark)
Acid
69
What conjugate base does water form when reacting with strong acids? (1 mark)
H3O+
70
What conjugate acid does water form when reacting with strong acids? (1 mark)
OH-
71
What is the dissociation of a strong acid commonly simplified to? (1 mark)
HA(aq) —> H+ (aq) + A- (aq)
72
What is the concentration of H+ ions in a strong acid with two hydrogen, and why? (2 marks)
Twice the concentration of the acid, because two H+ ions fully dissociate form each molecule.
73
What is a strong acid, regarding dissociation? (1 mark)
A strong acid completely dissociates in aqueous solution.
74
What is a weak acid, regarding dissociation? (1 mark)
A weak acid partially dissociates in aqueous solution.
75
What is Ka? (1 mark)
The acid dissociation constant.
76
What condition changes Ka? (1 mark)
Temperature
77
What does a large value of Ka indicate? (1 mark)
That the equilibrium is to the right (towards the products).
78
What temperature are values of Ka usually standardised at? (1 mark)
25 degrees
79
What is the general formula for Ka? (2 marks)
Ka= ([H+ (aq)][A- (aq)]) / [HA (aq)]
80
What does a larger value of Ka indicate, regarding dissociation, why? (1 mark)
Greater dissociation, because the concentration if H+ ions are on top.
81
What equation links Ka and pKa? (1 mark)
pKa = -log(Ka)
82
What does a high value of pKa indicate? (1 mark)
The higher it is, the weaker the acid.
83
What two things does [H+] rely on? (2 marks)
[HA]- concentration of the acid
Ka- the acid dissociation constant
84
What two approximations are used when calculating the Ka of weak acids? (4 marks)
1. That [H+]eqm = [A-]eqm
because HA dissociates equally.
2. That [HA]eqm = [HA]start
because the dissociation of the weak acids is small you can neglect the increase from start to equilibrium.
85
Using the two approximations, what can the expression for Ka be simplified to for weak acids? (2 marks)
Ka= [H+]^2/ [HA]
86
In weak acids, what is wrong with the approximation that states that [H+]=[A-]? (3 marks)
It assumes that the dissociation of water is negligible.
This approximation does not work for very weak acids or very dilute solutions (as HA does not dissociate as much or there is more water to dissociate).
87
In weak acids, what is wrong with the approximation that states that:
[HA]eqm = [HA]start ? (3 marks)
It assumes that the concentration of the acid is much greater than [H+] at equilibrium.
This approximation does not work for stronger acids or for very dilute solutions.
88
What is a strong base? (1 mark)
An alkali that completely dissociates in solution.
89
What is the concentration of water? (1 mark)
55.6moldm-3
90
How do you calculate the concentration of water? (3 marks)
For 1 dm3 of water, the mass is 1000g (since 1cm3=1g of water).
Using moles= mass/Mr
1000/18= 55.6 moles
Using concentration= moles/volume
55.6 moles/ 1dm3 = 55.6 moldm-3
91
What is Kw? (1 mark)
The ionic product of water.
92
What is the equation for the ionic product of water in any aqueous solution? (1 mark)
Kw= [H+(aq)] x [OH-(aq)]
93
What does Kw vary with? (1 mark)
Temperature
94
What is the value of Kw at 25 degrees? (1 mark)
1.00 x 10^-14 mol2dm-6
95
What is a buffer solution? (2 marks)
Buffers are solutions that can resist changes in pH, despite the addition of small quantities of acids or alkalis.
96
What is an acidic buffer? (1 mark)
A mixture of a weak acid and it’s conjugate base.
97
What happens if the conjugate base component of the buffer solution gets used up? (1 mark)
The buffer solution would not work for an acid.
98
Describe two ways in which buffer solutions can be prepared, and where the conjugate base comes from in each. (4 marks)
1. Weak acid + one of its salts --> the salt is the source of the conjugate base.
2. Weak acid (excess) + alkali --> The weak acid becomes partially neutralised by the alkali, forming the conjugate base.
99
Describe how a buffer solution counteracts a small amount of acid being added. (3 marks)
If an acid is added:
1. [H+] increases
2. H+ reacts with A-
3. Equilibrium position shifts to the left, removing most of the H+ ions
100
Describe how a buffer solution counteracts a small amount of alkali being added. (3 marks)
If an alkali is added:
1. [OH] increases
2. H+ reacts with OH-
3. HA dissociates. the equilibrium shifts to the right, restoring most of the H+
101
When is a buffer most effective? (1 mark)
When [HA(aq)] = [A-(aq)]
102
When [HA(aq)] = [A-(aq)], what is the value of pH? (1 mark)
pH = pKa of HA
103
How do you calculate the pH of a buffer solution prepared by mixing a weak acid and its salt? (3 marks)
1. Rearrange the Ka expression:
[H+]= Ka x [HA]/[A-]
2. Use pH= -log[H+(aq)]
104
How do you calculate the pH of a buffer solution prepared by partial neutralisation? (3 marks)
1. Find the excess moles of HA
2. Use Ka expression (with [HA]= excess HA/volume)
3. Use pH= -log[H+(aq)]
105
What is the really quick equation you can learn to calculate pH? (2 marks)
pH= pKa + log([A-]/[HA])
106
State the equilibrium equation for a buffer that contains equal concentrations of butanoic acid and sodium butanoate. (2 marks)
CH3(CH2)2COOH (aq) <---> H+ (aq) + CH3(CH2)2COO- (aq)
107
What pH does blood plasma need to be maintained at? (1 mark)
Between 7.35 and 7.45
108
How is pH of the blood maintained? (1 mark)
By a mixture of buffers.
109
What is the most important buffer system used to control the pH of the blood? (2 marks)
Carbonic acid and hydrogen carbonate ions.
H2CO3/HCO3-
110
What could happen if the pH of the blood rises above 7.45? (1 mark)
Alkalosis
111
State two symptoms of alkalosis. (2 marks)
Nausea
Muscle spasms
Light-headedness
112
What could happen if the pH pf the blood falls below 7.35 (1 mark)
Acidosis
113
State two symptoms of acidosis. (2 marks)
Fatigue
Shortness of breath
Shock or death
114
How does the body prevent a build up of carbonic acid? (2 marks)
It converts the carbonic acid to water and carbon dioxide.
The carbon dioxide is then exhaled.
115
How does the body ensure the concentration of hydrogen carbonate ions is not too high? (1 mark)
Kidney excretes less hydrogen carbonate ions
116
How many decimal places does a pH meter usually read? (1 mark)
2 decimal places
117
Describe how you would monitor the pH as an aqueous bas is added to an acid solution. (5 marks)
1. Measure volume of acid into a conical flask, using a pipette.
2. Put electrode of pH meter in flask.
3. Add base gradually, using a burette, swirling and recording the pH and volume of base added at regular intervals.
4. Repeat until the pH changes more rapidly, then add dropwise until rate slows.
5. Add faster again, until an excess has been added and the pH has been basic (with little change) for several additions.
6. Plot a graph of pH/total volume added.
118
How could you automate the monitoring of the pH of a titration? (2 marks)
Attach the pH meter to a data logger
Use a magnetic stirrer in the flask
Graph plotted automatically using appropriate software
119
What is the equivalence point? (1 mark)
The volume of solution that exactly reacts with the volume of the other solution.
120
What is an acid-base indicator? (1 mark)
A weak acid that has a different colour from its conjugate base.
121
What colour is methyl orange in a weak acid? (1 mark)
Red
122
What colour is methyl orange in a conjugate base? (1 mark)
Yellow
123
What colour is the end point of a titration indicated by when using methyl orange? (1 mark)
Orange
124
What happens when a basic solution is added to methyl orange? (4 marks)
1. Solution is initially red.
2. OH- ions react with the H+ ions in the indicator, forming water.
3. The weak acid in the indicator dissociates more, shifting the position of equilibrium to the right.
4. The colour changes, first to orange then to yellow.
125
What happens when an acid solution is added to methyl orange? (4 marks)
1. Solution is initially yellow
2. H+ ions react with the conjugate base in the indicator (A-)
3. The equilibrium shifts toward the left
4. The colour changes, first to orange then to red.
126
What colour is bromothymol blue in a weak acid? (1 mark)
Yellow
127
What colour is bromothymol in a conjugate base? (1 mark)
Blue
128
What colour is phenolphthalein in a weak acid? (1 mark)
Clear
129
What colour is phenolphthalein in a conjugate base? (1 mark)
Pink
130
What is the pH at the equivalence point for a strong acid-strong base/ weak acid-weak base titration? (1 mark)
pH= 7
131
What is the pH at the equivalence point for a strong acid-weak base titration? (1 mark)
pH < 7
132
What is the pH at the equivalence point for a weak acid-strong base titration? (! mark)
pH > 7
133
Define lattice enthalpy change. (2 marks)
The enthalpy change that accompanies the formation of one mile of an ionic compound from its gaseous ions.
134
Define enthalpy change of atomisation. (2 marks)
The enthalpy change that occurs when the formation of one mole of gaseous atoms from the element in its standard state.
135
Define first electron affinity. (2 marks)
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
136
Why is the second electron affinity endothermic. (2 marks)
In the second one, the electron is being gained by a negative ion, this increases repulsion, so energy must be put in to force the e- onto the ion.
137
Describe the steps required to form a giant ionic lattice. (3 marks)
Formation of gaseous atoms
Formation of gaseous ions
Lattice formation
138
Define enthalpy change of formation. (2 marks)
The enthalpy charge when one mole of a compound is formed from its elements.
139
Define bond dissociation enthalpy. (2 marks)
The bond dissociation enthalpy is the standard enthalpy change when 1 mole of a covalent bond is broken down into two gaseous atoms.
140
Define first ionisation energy. (2 marks)
The enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a 1+ charge.
141
Define enthalpy change of hydration. (1 mark)
The enthalpy change when 1 mole of gaseous ions become aqueous ions.
142
Define standard enthalpy change of solution. (2 marks)
The enthalpy change when one mole of a solute dissolved in a solvent.
143
What is the equation involving specific heat capacity and mass of solution? (1 mark)
q=mc x change in T
144
What two enthalpy changes are used to calculate enthalpy change of solution? (2 marks)
Lattice is enthalpy change
Enthalpy of hydration
145
What two factors affect lattice enthalpy? (2 marks)
Ionic size
Ionic charge
146
What two factors affect enthalpy change of hydration? (2 marks)
Ionic size
Ionic charge
147
How does ionic size affect lattice enthalpy? (2 mark)
As ionic radius increases, attraction between ions decreases, so lattice enthalpy becomes less negative.
148
How does ionic size affect hydration enthalpy? (2 mark)
As ionic radius increases, attraction between the ions and water decreases, therefore enthalpy of hydration is less negative.
149
How does ionic charge affect lattice enthalpy? (2 marks)
As ionic charge increases, attraction between ions increases, so lattice enthalpy becomes more negative.
150
How does ionic charge affect hydration enthalpy? (2 marks)
As ionic charge increases, attraction between ions and water molecules increases, so hydration energy becomes more negative.
151
Should a compound with endothermic enthalpy change of solution dissolve? (1 mark)
Yes
152
What is entropy? (2 marks)
The dispersal of energy within the chemicals making up a chemical system. The disorder of a chemical system.
153
Is the entropy greater in a gas of a liquid, why? (3 marks)
Gas
The system is more random, so energy is spread out more
In a liquid, the system is less random, energy is more concentrated, so entropy is lower.
154
How does Mr affect entropy? (2 marks)
The higher the Mr of a substance, the higher the entropy.
155
Explain the effect of a higher Mr on entropy. (2 marks)
More electrons, the number of ways of arranging particles increases with the number of particles. So entropy is higher.
156
Explain the effect of mixing on entropy. (2 marks)
Mixing increases the entropy of a solution, because there are a greater number of ways of rearranging the particles.
157
Why does sodium chloride dissolve? (3 marks)
Positive changes in entropy favour chemical and physical changes.
Whilst in terms of enthalpy NaCl should not dissolve, there is a positive entropy change as the ions and water molecules **mix**.
158
What is the unit for entropy? (1 mark)
JK-1mol-1
159
define free energy change. (1 mark)
The overall change in energy during a chemical reaction.
160
What is free energy made up of? (2 marks)
Enthalpy change
Entropy change
161
Define enthalpy change. (2 marks)
The heat transfer between the chemical system and its surroundings.
162
What is the equation for free energy? (2 marks)
Free energy= enthalpy change - (temperature x entropy change)
163
When is the reaction feasible? (1 mark)
When free energy < 0
164
When is a reaction not feasible? (1 mark)
When free energy > 0
165
What is the value of free energy at the minimum temperature for feasibility? (1 mark)
0
166
What is a reducing agent? (1 mark)
The species in a reaction which adds electrons to another species.
167
What is an oxidising agent? (1 mark)
A species in a reaction which takes away electrons from another species.
168
Does an oxidising agent get oxidised or reduced? (1 mark)
Reduced
169
Does a reducing agent get oxidised or reduced? (1 mark)
Oxidised
170
What does an increase in oxidation number indicate? (1 mark)
Oxidation
171
What does a decrease in oxidation number indicate? (1 mark)
Reduction
172
When writing half equation, what would you do if there was oxygen on the left but not on the right hand side of the equation? (2 marks)
Add water to the right hand side and then balance the equation by adding the correct number of H+ ions to the left.
173
How do you combine half equations? (2 marks)
Make the number of electrons the same in both.
Combine them.
Cancel out any species which are the same on both sides.
174
What colour is potassium manganate, how does this affect reading the level on the Burettes during titrations? (2 marks)
Dark pink/purple
Meniscus is read at the top, as it is too dark to see the bottom
175
How is the end point indicated during a potassium manganate titration? (1 mark)
First permanent pink colour
176
Is the thiosulfate or iodine reduced in a iodine/thiosulfate titration? (1 mark)
Iodine
177
Is the thiosulfate or iodine oxidised in a iodine/thiosulfate titration? (1 mark)
Thiosulfate
178
What is the equation for the oxidation of a thiosulfate ion? (2 marks)
2S2O3 2- —> S4O6 2- + 2e-
179
How is the end point detected in a iodine/thiosulfate titration? (3 marks)
Add the thiosulfate solution to the iodine solution until there is a colour change of orange to straw colour.
Then add a small amount of starch (this forms a black colour).
Continue adding the thiosulfate, until the solution is clear.
This is the end point.
180
Why is starch used in an iodine/thiosulfate titration? (1 mark)
It is hard to see the end point of the reaction, as it changes from a pale yellow to clear.
181
What oxidising agents can be used to titrate a thiosulfate solution? (3 marks)
I2
ClO-
Cu2+
182
How are samples of copper analysed? (3 marks)
The alloy is dissolved in HNO3, and then neutralised.
The Cu2+ is then reacted with I- to form I2 and CuI.
This brown mixture is titrated with Na2S2O3.
183
What colour is a mixture of I2 and CuI? (1 mark)
Brown
184
What is MnO4- reduced to? (1 mark)
Mn2+
185
What is Cr2O72- reduced to? (1 mark)
Cr3+
186
What does a voltaic cell do? (1 mark)
Converts chemical energy into electrical energy.
187
How do voltaic cells convert chemical energy into electrical energy? (1 mark)
Redox reactions, the movement of electrons from this.
188
What do half cells contain? (1 mark)
Chemical species present in a redox half equation.
189
How many half cells make up a voltaic cell? (1 mark)
Two
190
In a cell, why can chemicals not mix? (1 mark)
Electrons would flow in an uncontrolled way and heat energy would be released.
191
What is a metal/metal ion half-cell? (1 mark)
A metal rod dipped into solution of its aqueous metal ion.
192
What is the phase boundary in a metal/metal ion half-cell? (1 mark)
Where are the metal is in contact with its ions.
193
What is set up at the phase boundary? (1 mark)
An equilibrium.
194
What does an ion/ion half-cell contain? (1 mark)
Ions of the same element in different oxidation states.
A platinum electrode.
195
Why is a platinum electrode used in an ion/ion half-cell? (1 mark)
Because there is no metal to transport electrons.
196
Does the electrode with more or less reactive metal lose electrons and what is this electrode called? (2 marks)
The electrode with more reactive metal loses electrons, this is the negative electrode.
197
Does the electrode with more or less reactive metal gain electrons and what is this electrode called? (2 marks)
The electrode with less reactive metal gains electrons, this is the positive electrode.
198
How is a standard electrode potential found? (1 mark)
An electrode is connected to a standard hydrogen half-cell, under standard conditions:
199
What are the standard conditions used when finding a standard electrode potential? (1 mark)
Concentrations of all solutions are 1moldm-3.
Temperature is 298K.
Pressure is 100kPa
200
Define the term standard electrode potential. (2 marks)
Standard electrode potential is the e.m.f of a half-cell connected to a standard hydrogen half-cell under standard conditions.
201
What does e.m.f mean? (2 marks)
Electromotive force: the maximum potential difference between two electrodes.
202
What is the standard electrode potential of hydrogen? (1 mark)
0V
203
If the standard electrode potential is more negative, then is it oxidised or reduced? (1 mark)
Oxidised
204
What does a salt bridge allow? (1 mark)
Ions to flow
205
If the standard electrode potential is more positive, then is it oxidised or reduced? (1 mark)
Reduced
206
How do you prepare a salt bridge? (2 marks)
Soak a strip of filter paper in a saturated aqueous solution of potassium nitrate.
207
How do you calculate the standard cell potential from standard electrode potentials? (1 mark)
Cell= positive electrode — negative electrode
208
In terms of electrode potential, how can the reaction between two systems be predicted (Will it happen?)? (2 marks)
A reaction should take place if the redox system of the oxidising agent has a more positive value than the redox system of the reducing agent.
209
Why is concentration a limitation of using standard electrode potentials to predict the feasibility of reactions? (2 marks)
Standard use 1moldm-3.
If the concentration used is different from this, the electrode potential will be different from this value.
210
State 2 limitations of using standard electrode potentials to predict the feasibility of reactions? (2 marks)
The predictions will be wrong if :
The activation energy separating reactants and products is too high.
The conditions are not standard (conc, pressure, temp)
211
Explain what the statement ‘the activation energy separating reactants and products is too high’ means when explaining the limitations of using electrode potentials to predict feasibility of reactions. (2 marks)
The reaction is feasible but not spontaneous.
212
Are primary cells rechargeable? (1 mark)
No
213
Are secondary cells rechargeable? (1 mark)
Yes
214
How do fuel cells create a voltage? (1 mark)
Uses energy from the reaction of a fuel with oxygen.
215
Fuel cells can operate continuously if supplied with…… (2 marks)
Oxygen **and** fuel
216
What is the most common type of fuel cell? (1 mark)
Hydrogen
217
Explain why hydrogen fuel cells maintain a constant voltage. (1 mark)
They are continuously fed with hydrogen and oxygen.
218
Where are the d-block elements located on the periodic table? (1 mark)
In the middle
In groups 3-12
219
Give 3 properties of d-block elements. (3 marks)
Metallic
High melting and boiling points
Conduct electricity and heat
Shiny in appearance
220
What makes a d-block element a d-block element? (1 mark)
A d sub-shell is being filled (4s fills before 3d)
221
What are the two exceptions to the following rule:
'the 4s shell fills before the 3d shell'. (2 marks)
Chromium
Copper
222
Why are chromium and copper's 4 sub-shells not full? ( 2 marks)
The d5 and d10 subshells provide additional stability to the atoms.
223
What is a transition element? (1 mark)
A d-block element that can form at least one ion with a partially filled d-orbital.
224
Not all d-block elements are transition metals, give two examples that fit this description. (2 marks)
Scandium
Zinc
225
Why is scandium not a transition metal? (2 marks)
Scandium only forms Sc3+ by loss of 2 4s and 1 3d electrons, the resulting ion has no electrons a d-orbital.
226
Why is zinc not a transition metal? (2 marks)
Zinc only forms Zn2+ by loss of 2 4s, the resulting ion has a full d-orbital.
227
Give three properties of transition elements. (3 marks)
Form coloured compounds
The elements and compounds can act as catalysts
They readily change oxidation states.
228
State the catalyst used in the Haber process. ( 1mark)
Iron
229
What is the catalyst used in the contact process? (1 mark)
Vandium oxide
230
What makes transition metals good catalysts? (1 mark)
They are good at adsorbing substances onto their surface.
231
What is a complex ion? (1 mark)
One or more molecules/ negatively charged ions bonded to a central metal ion.
232
What are the molecules/ negative ions bonded to the central metal ion called in a complex ion? (1 mark)
Ligands
233
Define the term ligand. (1 mark)
A molecule or ion that donates a pair of electrons t a central ion to form a dative covalent bond.
234
What is a dative covalent bond? (1 mark)
When one atom provides both of the electrons in a covalent bond.
235
What does the coordination number tell you about a complex ion? (1 mark)
The coordination number indicates the number of covalent bonds attached to the central metal ion.
236
What is a mondentate ligand? (1 mark)
A ligand that can donate one pair of electrons to a central metal ion.
237
What is a bidentate ligand? (1 mark)
A ligand that can donate two pairs of electrons to a central metal ion.
238
What is the shape and bond angle of 6-coordinate complexes? (1 mark)
Octahedral
90 degrees
239
What is the coordinate number of an octahedral complex? (1 mark)
6
240
What are the shape(s) and bond angle(s) of 4-coordinate complexes? (3 marks)
tetrahedral- 109.5 degrees
square planar- 90 degrees
241
What is the coordinate number of a tetrahedral complex? (1 mark)
4
242
In what elements do square planar shapes occur? (3 marks)
Gold (III)
Platinum (II)
Palladium (II)
243
What is the bond angle of a tetrahedral complex ion? (1 mark)
109.5 degrees
244
What is the bond angle of a square planar complex ion? (1 mark)
90 degrees
245
What types of stereoisomerism can be displayed in complex ions? (2 marks)
Cis-trans isomerism
Optical isomerism
246
In what type of complex ions does cis-trans isomerism occur? (2 marks)
Square planar
Octahedral
247
What makes a cis complex ion cis? ( 2 marks)
Identical groups are adjacent.
90 degrees between identical groups.
248
What makes a trans complex ion trans? ( 2 marks)
Identical groups are opposite.
180 degrees between identical groups.
249
What are optical isomers? (1 mark)
Non-superimposable mirror images of each other.
250
In what type of complex ions does optical isomerism occur? (2 marks)
Octahedral, containing two or more bidentate ligands.
251
How does cis-platin treat cancer? (2 marks)
By forming a platinum complex inside of a cell which binds to the DNA of cancer cells and prevents it from replicating.
252
What is ligand substitution? (1 mark)
When one ligand in a complex ion is replaced by another ligand.
253
What ion is formed when copper sulfate is dissolved in water? (1 mark)
[Cu(H2O)6]2+
254
What colour is the solution formed when copper sulfate is dissolved in water? (1 mark)
Pale blue
255
What happens when copper sulfate is dissolved in water and then reacted with excess ammonia? (3 marks)
The pale blue solution changes to a dark blue solution.
Four ammonia ligands replace four of the water ligands.
Two different reactions take place; first a precipitate forms (Cu(OH)2), it then dissolves in the excess ammonia.
256
What happens when copper sulfate is dissolved in water and then reacted with excess hydrochloric acid? (3 marks)
The pale blue solution changes to a yellow solution.
Four chloride ligands replace the six water ligands.
The solution changes to green before going to yellow, as the two colours mix.
257
What complex ion is formed when chromium (III) potassium surface is dissolved in water? (1 mark)
[Cr(H2O)6]3+
258
What complex ion is formed when chromium (III) sultans is dissolved in water? (1 mark)
[Cr(H2O)5SO4]+
259
What happens when chromium (III) potassium sulfate is dissolved in water and then reacted with excess ammonia? (4 marks)
[Cr(H2O)6]3+ is formed, then reacted with ammonia to form [Cr(OH)3] (a precipitate).
Changing colour from purple to grey-green.
This then dissolved in the excess ammonia to form [Cr(NH3)6]3+
Changing colour from grey-green to violet.
260
Why is it dangerous to inhale CO? (2 marks)
CO can also bind to the iron in haemoglobin, and binds more strongly than oxygen, the bond is irreversible, preventing transport of oxygen.
261
Is Cu(OH)2 soluble in excess ammonia? (1 mark)
No
262
Is Cr(OH)3 soluble in excess NaOH? (1 mark)
Yes
263
Is Fe(OH)2 soluble in excess ammonia? (1 mark)
No
264
Is Fe(OH)3 soluble in excess NaOH? (1 mark)
No
265
Is Mn(OH)2 soluble in excess NaOH? (1 mark)
Yes
266
What colour is MnO4-? (1 mark)
Purple
267
What colour is Cr2O72-? (1 mark)
Orange
268
What colour is Fe3+? (1 mark)
Orange-brown
269
What colour is I2? (1 mark)
Brown
270
What colour is Cr3+? (1 mark)
Green
271
Give an equation for the oxidation of Cr3+ to Cr2O42-. (3 marks)
3H2O2 + 2Cr3+ + 10OH- —> 2CrO42- + 8H2O
272
What colour is Cu2+? (1 mark)
Pale blue
273
Suggest why the entropy of water is zero at 0K. (1 mark)
There is no disorder.
274
Define entropy. (1 mark)
The level of disorder of a reaction.
