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Chemistry Paper 1 > Module 5 > Flashcards

Module 5 Flashcards

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1
Q

What is rate of reaction? (1 mark)

A

Quantity reacted or produced/ change in time

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2
Q

What is the shorthand for concentration of A? (1 mark)

A

[A]
Must be square brackets

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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’

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4
Q

What is the order of the reaction if a reactant has no effect on the rate? (1 mark)

A

0

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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

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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

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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.

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8
Q

How do you work out overall order? (1 mark)

A

The sum of all orders with respect to each reactant.

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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

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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).

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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.

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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)

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13
Q

What does the concentration-time graph of a zero-order reaction look like? (2 marks)

A

Straight line
Negative gradient

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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).

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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)

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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.

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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.

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18
Q

How do you calculate k from half life (for a first order reaction)?

A

k= ln2/ half life

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19
Q

What does the rate-concentration graph look like for a zero order reaction? (1 mark)

A

Horizontal straight line

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20
Q

What does the rate-concentration graph look like for a first order reaction? (1 mark)

A

Straight line through origin.

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21
Q

What does the rate-concentration graph look like for a second order reaction? (2 mark)

A

Upward curve with increasing gradient.

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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

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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]

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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.

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25
Q

Describe the clock reaction. (3 marks)

A

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.

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26
Q

What do iodine clocks rely on? (2 marks)

A

The formation of iodine (the colour would change from orange to black).

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27
Q

How accurate are clock reactions, over time?

A

It measures the average rate of change in reactant over time, so the less of a reaction taken place, the more accurate it is.

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28
Q

What is the slowest step in a reaction mechanism called? (1 mark)

A

The rate-determining step

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29
Q

What does the rate equation contain? (1 mark)

A

Only the reactants from the rate determining step.
E.g. EF + F —> G
rate= k[E][F]^2

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30
Q

What happens to the rate constant as temperature increases? (1 mark)

A

The rate constant increases.

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31
Q

Why does the rate constant increase when temperature increases? (5 marks)

A

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.

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32
Q

What does the exponential factor, in the Arrhenius equation, represent? (1 mark)

A

The proportion of molecules/particles that exceed Ea.

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33
Q

What does the frequency factor, in the Arrhenius equation, take into account? (2 marks)

A

The frequency of collisions
with the correct orientation.

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34
Q

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?

A

lnk = -Ea/RT • 1/T + lnA
y = m • x + c

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35
Q

If you plot a graph of lnk against 1/T, what is the gradient (according to the Arrhenius equation)?

A

-Ea/R

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36
Q

If you plot a graph of lnk against 1/T, what is the y-intercept (according to the Arrhenius equation)?

A

lnA

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37
Q

What are the two main types of equilibria? (2 marks)

A

Homogeneous
Heterogeneous

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38
Q

What is homogeneous equilibrium? (2 marks)

A

Species all the same state.
Everything is included in the equation for Kc

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39
Q

What is heterogeneous equilibrium? (2 marks)

A

Species have different states.
Solids and liquids are not included in equation for Kc.

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40
Q

Why are solids and liquids not included in a heterogenous Kc equation? (1 mark)

A

The concentration of solids and liquids are essentially constant.

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41
Q

What do the values in the square brackets in the Kc equation represent? (2 marks)

A

Concentrationof species
At equilibrium

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42
Q

What environmental factor affects K? (1 mark)

A

Temperature

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43
Q

What happens to K when temperature increases, in an exothermic reaction? (1 mark)

A

Decreases

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44
Q

What happens to K when temperature increases, in an endothermic reaction? (1 mark)

A

Increases

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45
Q

Describe the effect of increasing the pressure on Kc for a reaction with less moles on the right. (3 marks)

A

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.

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46
Q

Describe what happens to Kp when the temperature is increased, in an exothermic reaction. (5 marks)

A

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.

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47
Q

Describe what happens to Kp when the temperature is increased, in an endothermic reaction. (5 marks)

A

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.

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48
Q

What is the equation for mole fraction? (2 marks)

A

x(A) = no. of moles of A/ total no. of moles in gas mixture

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49
Q

What is the equation for partial pressure? (2 marks)

A

Partial pressure = mole fraction of A x total pressure

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50
Q

What is the relationship between partial pressures and total pressure? (1 mark)

A

Sum of partial pressures = total pressure

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51
Q

What state does the expression for Kp only contain? (1 mark)

A

Gas

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52
Q

What are the three acceptable units for partial pressure? (3 marks)

A

kPa
Pa
atm

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53
Q

What is an acid, according to Brønsted-Lowry? (1 mark)

A

An acids is a proton donor.

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54
Q

What is a base, according to Brønsted-Lowry? (1 mark)

A

A base is a proton acceptor.

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55
Q

What is a conjugate acid-pair, give an example? (2 marks)

A

A conjugate acid-pair is two species that can be interconverted by transfer of a proton (H+ ion).

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56
Q

What is a monobasic acid, give an example? (2 marks)

A

An acid which can donate one proton.
HCl, CH3COOH, HNO3

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57
Q

What is a dibasic acid, give an example? (2 marks)

A

An acid which can donate 2 protons.
H2SO4, H2CO3

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58
Q

What is a tribasic acid, give an example? (2 marks)

A

An acid which can donate 3 protons.
H3BO3, H3PO4

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59
Q

What are two ways a neutralisation equation can be written? (2 marks)

A

H3O+ + OH- —> 2H2O

and

H+ + OH- —> H2O

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60
Q

Who came up with the pH scale? (1 mark)

A

Søren Sørensen

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61
Q

What is the pH scale? (1 mark)

A

Numerical scale for measuring hydrogen ion concentrations.

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62
Q

What are the pH values of acidic, alkaline, and neutral solutions? (3 marks)

A

<7 is acidic
7< is alkaline
=7 is neutral

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63
Q

What is the equation that represents the relationship between pH and the concentration of H+ ions? (2 marks)

A

pH= -log[H+ (aq)]
or 10^-pH = [H+ (aq)]

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64
Q

What is the concentration of H+ ions in a strong acid with one hydrogen, and why? (2 marks)

A

The same as the concentration of the acid, because the acid completely disassociates.

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65
Q

Dilution changes the pH of a solution, true or false? (1 mark)

A

True

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66
Q

What is a chemical called when it can act as an acid or a base? (1 mark)

A

Amphoteric

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67
Q

Does water act as an acid or base when reacting with strong acids? (1 mark)

A

Base

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68
Q

Does water act as an acid or base when reacting with weak acids? (1 mark)

A

Acid

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69
Q

What conjugate base does water form when reacting with strong acids? (1 mark)

A

H3O+

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70
Q

What conjugate acid does water form when reacting with strong acids? (1 mark)

A

OH-

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71
Q

What is the dissociation of a strong acid commonly simplified to? (1 mark)

A

HA(aq) —> H+ (aq) + A- (aq)

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72
Q

What is the concentration of H+ ions in a strong acid with two hydrogen, and why? (2 marks)

A

Twice the concentration of the acid, because two H+ ions fully dissociate form each molecule.

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73
Q

What is a strong acid, regarding dissociation? (1 mark)

A

A strong acid completely dissociates in aqueous solution.

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74
Q

What is a weak acid, regarding dissociation? (1 mark)

A

A weak acid partially dissociates in aqueous solution.

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75
Q

What is Ka? (1 mark)

A

The acid dissociation constant.

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76
Q

What condition changes Ka? (1 mark)

A

Temperature

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77
Q

What does a large value of Ka indicate? (1 mark)

A

That the equilibrium is to the right (towards the products).

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78
Q

What temperature are values of Ka usually standardised at? (1 mark)

A

25 degrees

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79
Q

What is the general formula for Ka? (2 marks)

A

Ka= ([H+ (aq)][A- (aq)]) / [HA (aq)]

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80
Q

What does a larger value of Ka indicate, regarding dissociation, why? (1 mark)

A

Greater dissociation, because the concentration if H+ ions are on top.

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81
Q

What equation links Ka and pKa? (1 mark)

A

pKa = -log(Ka)

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82
Q

What does a high value of pKa indicate? (1 mark)

A

The higher it is, the weaker the acid.

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83
Q

What two things does [H+] rely on? (2 marks)

A

[HA]- concentration of the acid
Ka- the acid dissociation constant

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84
Q

What two approximations are used when calculating the Ka of weak acids? (4 marks)

A
  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.
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85
Q

Using the two approximations, what can the expression for Ka be simplified to for weak acids? (2 marks)

A

Ka= [H+]^2/ [HA]

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86
Q

In weak acids, what is wrong with the approximation that states that [H+]=[A-]? (3 marks)

A

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).

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87
Q

In weak acids, what is wrong with the approximation that states that:
[HA]eqm = [HA]start ? (3 marks)

A

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.

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88
Q

What is a strong base? (1 mark)

A

An alkali that completely dissociates in solution.

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89
Q

What is the concentration of water? (1 mark)

A

55.6moldm-3

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90
Q

How do you calculate the concentration of water? (3 marks)

A

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

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91
Q

What is Kw? (1 mark)

A

The ionic product of water.

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92
Q

What is the equation for the ionic product of water in any aqueous solution? (1 mark)

A

Kw= [H+(aq)] x [OH-(aq)]

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93
Q

What does Kw vary with? (1 mark)

A

Temperature

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94
Q

What is the value of Kw at 25 degrees? (1 mark)

A

1.00 x 10^-14 mol2dm-6

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95
Q

What is a buffer solution? (2 marks)

A

Buffers are solutions that can resist changes in pH, despite the addition of small quantities of acids or alkalis.

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96
Q

What is an acidic buffer? (1 mark)

A

A mixture of a weak acid and it’s conjugate base.

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97
Q

What happens if the conjugate base component of the buffer solution gets used up? (1 mark)

A

The buffer solution would not work for an acid.

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98
Q

Describe two ways in which buffer solutions can be prepared, and where the conjugate base comes from in each. (4 marks)

A
  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.
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99
Q

Describe how a buffer solution counteracts a small amount of acid being added. (3 marks)

A

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

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100
Q

Describe how a buffer solution counteracts a small amount of alkali being added. (3 marks)

A

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+

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101
Q

When is a buffer most effective? (1 mark)

A

When [HA(aq)] = [A-(aq)]

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102
Q

When [HA(aq)] = [A-(aq)], what is the value of pH? (1 mark)

A

pH = pKa of HA

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103
Q

How do you calculate the pH of a buffer solution prepared by mixing a weak acid and its salt? (3 marks)

A
  1. Rearrange the Ka expression:
    [H+]= Ka x [HA]/[A-]
  2. Use pH= -log[H+(aq)]
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104
Q

How do you calculate the pH of a buffer solution prepared by partial neutralisation? (3 marks)

A
  1. Find the excess moles of HA
  2. Use Ka expression (with [HA]= excess HA/volume)
  3. Use pH= -log[H+(aq)]
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105
Q

What is the really quick equation you can learn to calculate pH? (2 marks)

A

pH= pKa + log([A-]/[HA])

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106
Q

State the equilibrium equation for a buffer that contains equal concentrations of butanoic acid and sodium butanoate. (2 marks)

A

CH3(CH2)2COOH (aq) <—> H+ (aq) + CH3(CH2)2COO- (aq)

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107
Q

What pH does blood plasma need to be maintained at? (1 mark)

A

Between 7.35 and 7.45

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108
Q

How is pH of the blood maintained? (1 mark)

A

By a mixture of buffers.

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109
Q

What is the most important buffer system used to control the pH of the blood? (2 marks)

A

Carbonic acid and hydrogen carbonate ions.
H2CO3/HCO3-

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110
Q

What could happen if the pH of the blood rises above 7.45? (1 mark)

A

Alkalosis

111
Q

State two symptoms of alkalosis. (2 marks)

A

Nausea
Muscle spasms
Light-headedness

112
Q

What could happen if the pH pf the blood falls below 7.35 (1 mark)

A

Acidosis

113
Q

State two symptoms of acidosis. (2 marks)

A

Fatigue
Shortness of breath
Shock or death

114
Q

How does the body prevent a build up of carbonic acid? (2 marks)

A

It converts the carbonic acid to water and carbon dioxide.
The carbon dioxide is then exhaled.

115
Q

How does the body ensure the concentration of hydrogen carbonate ions is not too high? (1 mark)

A

Kidney excretes less hydrogen carbonate ions

116
Q

How many decimal places does a pH meter usually read? (1 mark)

A

2 decimal places

117
Q

Describe how you would monitor the pH as an aqueous bas is added to an acid solution. (5 marks)

A
  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
Q

How could you automate the monitoring of the pH of a titration? (2 marks)

A

Attach the pH meter to a data logger
Use a magnetic stirrer in the flask
Graph plotted automatically using appropriate software

119
Q

What is the equivalence point? (1 mark)

A

The volume of solution that exactly reacts with the volume of the other solution.

120
Q

What is an acid-base indicator? (1 mark)

A

A weak acid that has a different colour from its conjugate base.

121
Q

What colour is methyl orange in a weak acid? (1 mark)

A

Red

122
Q

What colour is methyl orange in a conjugate base? (1 mark)

A

Yellow

123
Q

What colour is the end point of a titration indicated by when using methyl orange? (1 mark)

A

Orange

124
Q

What happens when a basic solution is added to methyl orange? (4 marks)

A
  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
Q

What happens when an acid solution is added to methyl orange? (4 marks)

A
  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
Q

What colour is bromothymol blue in a weak acid? (1 mark)

A

Yellow

127
Q

What colour is bromothymol in a conjugate base? (1 mark)

A

Blue

128
Q

What colour is phenolphthalein in a weak acid? (1 mark)

A

Clear

129
Q

What colour is phenolphthalein in a conjugate base? (1 mark)

A

Pink

130
Q

What is the pH at the equivalence point for a strong acid-strong base/ weak acid-weak base titration? (1 mark)

A

pH= 7

131
Q

What is the pH at the equivalence point for a strong acid-weak base titration? (1 mark)

A

pH < 7

132
Q

What is the pH at the equivalence point for a weak acid-strong base titration? (! mark)

A

pH > 7

133
Q

Define lattice enthalpy change. (2 marks)

A

The enthalpy change that accompanies the formation of one mile of an ionic compound from its gaseous ions.

134
Q

Define enthalpy change of atomisation. (2 marks)

A

The enthalpy change that occurs when the formation of one mole of gaseous atoms from the element in its standard state.

135
Q

Define first electron affinity. (2 marks)

A

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
Q

Why is the second electron affinity endothermic. (2 marks)

A

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
Q

Describe the steps required to form a giant ionic lattice. (3 marks)

A

Formation of gaseous atoms
Formation of gaseous ions
Lattice formation

138
Q

Define enthalpy change of formation. (2 marks)

A

The enthalpy charge when one mole of a compound is formed from its elements.

139
Q

Define bond dissociation enthalpy. (2 marks)

A

The bond dissociation enthalpy is the standard enthalpy change when 1 mole of a covalent bond is broken down into two gaseous atoms.

140
Q

Define first ionisation energy. (2 marks)

A

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
Q

Define enthalpy change of hydration. (1 mark)

A

The enthalpy change when 1 mole of gaseous ions become aqueous ions.

142
Q

Define standard enthalpy change of solution. (2 marks)

A

The enthalpy change when one mole of a solute dissolved in a solvent.

143
Q

What is the equation involving specific heat capacity and mass of solution? (1 mark)

A

q=mc x change in T

144
Q

What two enthalpy changes are used to calculate enthalpy change of solution? (2 marks)

A

Lattice is enthalpy change
Enthalpy of hydration

145
Q

What two factors affect lattice enthalpy? (2 marks)

A

Ionic size
Ionic charge

146
Q

What two factors affect enthalpy change of hydration? (2 marks)

A

Ionic size
Ionic charge

147
Q

How does ionic size affect lattice enthalpy? (2 mark)

A

As ionic radius increases, attraction between ions decreases, so lattice enthalpy becomes less negative.

148
Q

How does ionic size affect hydration enthalpy? (2 mark)

A

As ionic radius increases, attraction between the ions and water decreases, therefore enthalpy of hydration is less negative.

149
Q

How does ionic charge affect lattice enthalpy? (2 marks)

A

As ionic charge increases, attraction between ions increases, so lattice enthalpy becomes more negative.

150
Q

How does ionic charge affect hydration enthalpy? (2 marks)

A

As ionic charge increases, attraction between ions and water molecules increases, so hydration energy becomes more negative.

151
Q

Should a compound with endothermic enthalpy change of solution dissolve? (1 mark)

A

Yes

152
Q

What is entropy? (2 marks)

A

The dispersal of energy within the chemicals making up a chemical system. The disorder of a chemical system.

153
Q

Is the entropy greater in a gas of a liquid, why? (3 marks)

A

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
Q

How does Mr affect entropy? (2 marks)

A

The higher the Mr of a substance, the higher the entropy.

155
Q

Explain the effect of a higher Mr on entropy. (2 marks)

A

More electrons, the number of ways of arranging particles increases with the number of particles. So entropy is higher.

156
Q

Explain the effect of mixing on entropy. (2 marks)

A

Mixing increases the entropy of a solution, because there are a greater number of ways of rearranging the particles.

157
Q

Why does sodium chloride dissolve? (3 marks)

A

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
Q

What is the unit for entropy? (1 mark)

A

JK-1mol-1

159
Q

define free energy change. (1 mark)

A

The overall change in energy during a chemical reaction.

160
Q

What is free energy made up of? (2 marks)

A

Enthalpy change
Entropy change

161
Q

Define enthalpy change. (2 marks)

A

The heat transfer between the chemical system and its surroundings.

162
Q

What is the equation for free energy? (2 marks)

A

Free energy= enthalpy change - (temperature x entropy change)

163
Q

When is the reaction feasible? (1 mark)

A

When free energy < 0

164
Q

When is a reaction not feasible? (1 mark)

A

When free energy > 0

165
Q

What is the value of free energy at the minimum temperature for feasibility? (1 mark)

A

0

166
Q

What is a reducing agent? (1 mark)

A

The species in a reaction which adds electrons to another species.

167
Q

What is an oxidising agent? (1 mark)

A

A species in a reaction which takes away electrons from another species.

168
Q

Does an oxidising agent get oxidised or reduced? (1 mark)

A

Reduced

169
Q

Does a reducing agent get oxidised or reduced? (1 mark)

A

Oxidised

170
Q

What does an increase in oxidation number indicate? (1 mark)

A

Oxidation

171
Q

What does a decrease in oxidation number indicate? (1 mark)

A

Reduction

172
Q

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)

A

Add water to the right hand side and then balance the equation by adding the correct number of H+ ions to the left.

173
Q

How do you combine half equations? (2 marks)

A

Make the number of electrons the same in both.
Combine them.
Cancel out any species which are the same on both sides.

174
Q

What colour is potassium manganate, how does this affect reading the level on the Burettes during titrations? (2 marks)

A

Dark pink/purple
Meniscus is read at the top, as it is too dark to see the bottom

175
Q

How is the end point indicated during a potassium manganate titration? (1 mark)

A

First permanent pink colour

176
Q

Is the thiosulfate or iodine reduced in a iodine/thiosulfate titration? (1 mark)

A

Iodine

177
Q

Is the thiosulfate or iodine oxidised in a iodine/thiosulfate titration? (1 mark)

A

Thiosulfate

178
Q

What is the equation for the oxidation of a thiosulfate ion? (2 marks)

A

2S2O3 2- —> S4O6 2- + 2e-

179
Q

How is the end point detected in a iodine/thiosulfate titration? (3 marks)

A

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
Q

Why is starch used in an iodine/thiosulfate titration? (1 mark)

A

It is hard to see the end point of the reaction, as it changes from a pale yellow to clear.

181
Q

What oxidising agents can be used to titrate a thiosulfate solution? (3 marks)

A

I2
ClO-
Cu2+

182
Q

How are samples of copper analysed? (3 marks)

A

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
Q

What colour is a mixture of I2 and CuI? (1 mark)

A

Brown

184
Q

What is MnO4- reduced to? (1 mark)

A

Mn2+

185
Q

What is Cr2O72- reduced to? (1 mark)

A

Cr3+

186
Q

What does a voltaic cell do? (1 mark)

A

Converts chemical energy into electrical energy.

187
Q

How do voltaic cells convert chemical energy into electrical energy? (1 mark)

A

Redox reactions, the movement of electrons from this.

188
Q

What do half cells contain? (1 mark)

A

Chemical species present in a redox half equation.

189
Q

How many half cells make up a voltaic cell? (1 mark)

A

Two

190
Q

In a cell, why can chemicals not mix? (1 mark)

A

Electrons would flow in an uncontrolled way and heat energy would be released.

191
Q

What is a metal/metal ion half-cell? (1 mark)

A

A metal rod dipped into solution of its aqueous metal ion.

192
Q

What is the phase boundary in a metal/metal ion half-cell? (1 mark)

A

Where are the metal is in contact with its ions.

193
Q

What is set up at the phase boundary? (1 mark)

A

An equilibrium.

194
Q

What does an ion/ion half-cell contain? (1 mark)

A

Ions of the same element in different oxidation states.
A platinum electrode.

195
Q

Why is a platinum electrode used in an ion/ion half-cell? (1 mark)

A

Because there is no metal to transport electrons.

196
Q

Does the electrode with more or less reactive metal lose electrons and what is this electrode called? (2 marks)

A

The electrode with more reactive metal loses electrons, this is the negative electrode.

197
Q

Does the electrode with more or less reactive metal gain electrons and what is this electrode called? (2 marks)

A

The electrode with less reactive metal gains electrons, this is the positive electrode.

198
Q

How is a standard electrode potential found? (1 mark)

A

An electrode is connected to a standard hydrogen half-cell, under standard conditions:

199
Q

What are the standard conditions used when finding a standard electrode potential? (1 mark)

A

Concentrations of all solutions are 1moldm-3.
Temperature is 298K.
Pressure is 100kPa

200
Q

Define the term standard electrode potential. (2 marks)

A

Standard electrode potential is the e.m.f of a half-cell connected to a standard hydrogen half-cell under standard conditions.

201
Q

What does e.m.f mean? (2 marks)

A

Electromotive force: the maximum potential difference between two electrodes.

202
Q

What is the standard electrode potential of hydrogen? (1 mark)

A

0V

203
Q

If the standard electrode potential is more negative, then is it oxidised or reduced? (1 mark)

A

Oxidised

204
Q

What does a salt bridge allow? (1 mark)

A

Ions to flow

205
Q

If the standard electrode potential is more positive, then is it oxidised or reduced? (1 mark)

A

Reduced

206
Q

How do you prepare a salt bridge? (2 marks)

A

Soak a strip of filter paper in a saturated aqueous solution of potassium nitrate.

207
Q

How do you calculate the standard cell potential from standard electrode potentials? (1 mark)

A

Cell= positive electrode — negative electrode

208
Q

In terms of electrode potential, how can the reaction between two systems be predicted (Will it happen?)? (2 marks)

A

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
Q

Why is concentration a limitation of using standard electrode potentials to predict the feasibility of reactions? (2 marks)

A

Standard use 1moldm-3.
If the concentration used is different from this, the electrode potential will be different from this value.

210
Q

State 2 limitations of using standard electrode potentials to predict the feasibility of reactions? (2 marks)

A

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
Q

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)

A

The reaction is feasible but not spontaneous.

212
Q

Are primary cells rechargeable? (1 mark)

A

No

213
Q

Are secondary cells rechargeable? (1 mark)

A

Yes

214
Q

How do fuel cells create a voltage? (1 mark)

A

Uses energy from the reaction of a fuel with oxygen.

215
Q

Fuel cells can operate continuously if supplied with…… (2 marks)

A

Oxygen and fuel

216
Q

What is the most common type of fuel cell? (1 mark)

A

Hydrogen

217
Q

Explain why hydrogen fuel cells maintain a constant voltage. (1 mark)

A

They are continuously fed with hydrogen and oxygen.

218
Q

Where are the d-block elements located on the periodic table? (1 mark)

A

In the middle
In groups 3-12

219
Q

Give 3 properties of d-block elements. (3 marks)

A

Metallic
High melting and boiling points
Conduct electricity and heat
Shiny in appearance

220
Q

What makes a d-block element a d-block element? (1 mark)

A

A d sub-shell is being filled (4s fills before 3d)

221
Q

What are the two exceptions to the following rule:
‘the 4s shell fills before the 3d shell’. (2 marks)

A

Chromium
Copper

222
Q

Why are chromium and copper’s 4 sub-shells not full? ( 2 marks)

A

The d5 and d10 subshells provide additional stability to the atoms.

223
Q

What is a transition element? (1 mark)

A

A d-block element that can form at least one ion with a partially filled d-orbital.

224
Q

Not all d-block elements are transition metals, give two examples that fit this description. (2 marks)

A

Scandium
Zinc

225
Q

Why is scandium not a transition metal? (2 marks)

A

Scandium only forms Sc3+ by loss of 2 4s and 1 3d electrons, the resulting ion has no electrons a d-orbital.

226
Q

Why is zinc not a transition metal? (2 marks)

A

Zinc only forms Zn2+ by loss of 2 4s, the resulting ion has a full d-orbital.

227
Q

Give three properties of transition elements. (3 marks)

A

Form coloured compounds
The elements and compounds can act as catalysts
They readily change oxidation states.

228
Q

State the catalyst used in the Haber process. ( 1mark)

A

Iron

229
Q

What is the catalyst used in the contact process? (1 mark)

A

Vandium oxide

230
Q

What makes transition metals good catalysts? (1 mark)

A

They are good at adsorbing substances onto their surface.

231
Q

What is a complex ion? (1 mark)

A

One or more molecules/ negatively charged ions bonded to a central metal ion.

232
Q

What are the molecules/ negative ions bonded to the central metal ion called in a complex ion? (1 mark)

A

Ligands

233
Q

Define the term ligand. (1 mark)

A

A molecule or ion that donates a pair of electrons t a central ion to form a dative covalent bond.

234
Q

What is a dative covalent bond? (1 mark)

A

When one atom provides both of the electrons in a covalent bond.

235
Q

What does the coordination number tell you about a complex ion? (1 mark)

A

The coordination number indicates the number of covalent bonds attached to the central metal ion.

236
Q

What is a mondentate ligand? (1 mark)

A

A ligand that can donate one pair of electrons to a central metal ion.

237
Q

What is a bidentate ligand? (1 mark)

A

A ligand that can donate two pairs of electrons to a central metal ion.

238
Q

What is the shape and bond angle of 6-coordinate complexes? (1 mark)

A

Octahedral
90 degrees

239
Q

What is the coordinate number of an octahedral complex? (1 mark)

A

6

240
Q

What are the shape(s) and bond angle(s) of 4-coordinate complexes? (3 marks)

A

tetrahedral- 109.5 degrees
square planar- 90 degrees

241
Q

What is the coordinate number of a tetrahedral complex? (1 mark)

A

4

242
Q

In what elements do square planar shapes occur? (3 marks)

A

Gold (III)
Platinum (II)
Palladium (II)

243
Q

What is the bond angle of a tetrahedral complex ion? (1 mark)

A

109.5 degrees

244
Q

What is the bond angle of a square planar complex ion? (1 mark)

A

90 degrees

245
Q

What types of stereoisomerism can be displayed in complex ions? (2 marks)

A

Cis-trans isomerism
Optical isomerism

246
Q

In what type of complex ions does cis-trans isomerism occur? (2 marks)

A

Square planar
Octahedral

247
Q

What makes a cis complex ion cis? ( 2 marks)

A

Identical groups are adjacent.
90 degrees between identical groups.

248
Q

What makes a trans complex ion trans? ( 2 marks)

A

Identical groups are opposite.
180 degrees between identical groups.

249
Q

What are optical isomers? (1 mark)

A

Non-superimposable mirror images of each other.

250
Q

In what type of complex ions does optical isomerism occur? (2 marks)

A

Octahedral, containing two or more bidentate ligands.

251
Q

How does cis-platin treat cancer? (2 marks)

A

By forming a platinum complex inside of a cell which binds to the DNA of cancer cells and prevents it from replicating.

252
Q

What is ligand substitution? (1 mark)

A

When one ligand in a complex ion is replaced by another ligand.

253
Q

What ion is formed when copper sulfate is dissolved in water? (1 mark)

A

[Cu(H2O)6]2+

254
Q

What colour is the solution formed when copper sulfate is dissolved in water? (1 mark)

A

Pale blue

255
Q

What happens when copper sulfate is dissolved in water and then reacted with excess ammonia? (3 marks)

A

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
Q

What happens when copper sulfate is dissolved in water and then reacted with excess hydrochloric acid? (3 marks)

A

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
Q

What complex ion is formed when chromium (III) potassium surface is dissolved in water? (1 mark)

A

[Cr(H2O)6]3+

258
Q

What complex ion is formed when chromium (III) sultans is dissolved in water? (1 mark)

A

[Cr(H2O)5SO4]+

259
Q

What happens when chromium (III) potassium sulfate is dissolved in water and then reacted with excess ammonia? (4 marks)

A

[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
Q

Why is it dangerous to inhale CO? (2 marks)

A

CO can also bind to the iron in haemoglobin, and binds more strongly than oxygen, the bond is irreversible, preventing transport of oxygen.

261
Q

Is Cu(OH)2 soluble in excess ammonia? (1 mark)

A

No

262
Q

Is Cr(OH)3 soluble in excess NaOH? (1 mark)

A

Yes

263
Q

Is Fe(OH)2 soluble in excess ammonia? (1 mark)

A

No

264
Q

Is Fe(OH)3 soluble in excess NaOH? (1 mark)

A

No

265
Q

Is Mn(OH)2 soluble in excess NaOH? (1 mark)

A

Yes

266
Q

What colour is MnO4-? (1 mark)

A

Purple

267
Q

What colour is Cr2O72-? (1 mark)

A

Orange

268
Q

What colour is Fe3+? (1 mark)

A

Orange-brown

269
Q

What colour is I2? (1 mark)

A

Brown

270
Q

What colour is Cr3+? (1 mark)

A

Green

271
Q

Give an equation for the oxidation of Cr3+ to Cr2O42-. (3 marks)

A

3H2O2 + 2Cr3+ + 10OH- —> 2CrO42- + 8H2O

272
Q

What colour is Cu2+? (1 mark)

A

Pale blue

273
Q

Suggest why the entropy of water is zero at 0K. (1 mark)

A

There is no disorder.

274
Q

Define entropy. (1 mark)

A

The level of disorder of a reaction.

Chemistry Paper 1 (3 decks)

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