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A level Chemistry > Unit 1.7 - Simple Equilibra and acid-base reactions > Flashcards

Unit 1.7 - Simple Equilibra and acid-base reactions Flashcards

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1
Q

What are the characteristics of chemical equilibrium?

A
  1. The reaction is reversible
  2. The equilibrium is dynamic (i.e - the reaction is still proceeding)
  3. The rate of the forward reaction is equal to the rate of the backward reaction
  4. At equilibrium, properties such as concentration and pressure are constant
  5. Equilibrium can only be attained in a closed system
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2
Q

Symbol for reversible reaction

A

—>
<—

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3
Q

—>
<— meaning

A

reversible reaction

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4
Q

What does it mean that the equilibrium is dynamic during chemical equilibrium?

A

The reaction is still proceeding

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5
Q

Dynamic equilibrium definition

A

A reversible reaction where the rate of the forward reaction is equal to the rate of the backward reaction

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6
Q

What are the observations we can make due to the fact that the rate of the forward reaction is equal to the rate of the backward reaction in chemical equilibrium?

A

No observable change in the system

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7
Q

Which properties are constant in chemical equilibrium?

A

Pressure and temperature, for example

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8
Q

In what type of system only can equilibrium be attained?

A

Closed

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9
Q

What’s a fizzy drink can an example of?

A

A closed system within which equilibrium can be attained

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10
Q

Example of a closed system

A

Fizzy drink can

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11
Q

Why would there be no observable change in a system in chemical equilibrium?

A

The rate of the forward reaction is equal to the rate of the backward reaction

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12
Q

What is “the rate of the forward reaction is equal to the rate of the backward reaction” the definition for?

A

Dynamic equilibrium

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13
Q

Compare a system in dynamic equilibrium in different conditions

A

Fixed conditions - stable
Sensitive to alterations in conditions

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14
Q

When is a system in dynamic equilibrium stable?

A

Under fixed conditions

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15
Q

What are the reactants and products constantly doing in a reversible reaction?

A

Reactants - constantly forming products
Products - constantly forming reactants

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16
Q

Describe the amount of products and reactants in a system in dynamic equilibium

A

Constant, not equal

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17
Q

Are the amount of reactants and products in a system in dynamic equilibrium equal?

A

No, but they are constant

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18
Q

What is a system in dynamic equilibrium sensitive to?

A

Alteration in conditions

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19
Q

Homogenous system

A

All the substances are in the same physical state (e.g - g)

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20
Q

What type of system is one where all of the substances are on the same physical state?

A

Homogenous

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21
Q

The Haber process equation + what is it an example of?

A

N2 (g) + 3H2 (g) —> 2NH3 (g)
<—

A homogenous system (all g)

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22
Q

Give two examples of homogenous systems

A
  1. Formation of ammonia in the haber process
  2. the esterification between an organic acid and an alcohol
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23
Q

Heterogeneous systems

A

The substances are in two or more physical states

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24
Q

What type of system is one where the substances are in two or more physical states?

A

Heterogeneous system

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25
Q

Le Chatelier’s Principle

A

If a system at equilibrium is subjected to a change, the position of equilibrium will move to counteract the change imposed

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26
Q

“If a system at equilibrium is subjected to a change, the position of equilibrium will move to counteract he change imposed” - What is this?

A

Le Chatelier’s Principle

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27
Q

Position of equilibrium

A

The equilibrium state under a particular set of conditions

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28
Q

What are the factors that affect the position of equilibrium?

A
  1. Catalysts (but not really)
  2. Concentration
  3. Pressure
  4. Temperature
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29
Q

What do the following factors all affect - catalyst, concentration, pressure and temperature?

A

The position of equilibrium

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30
Q

How do catalysts affect the position of equilibrium?

A

They increase the rates of the forward and backward reactions to the same extent, therefore they have no effect on the position of equilibrium

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31
Q

How does concentration effect the position of equilibrium?

A

It moves towards what we want more of (the thing that HASN’T increased in concentration)

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32
Q

If we have more reactants than products, how does the position of equilibrium move?

A

Starts at the left, so moves to the right to form more products

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33
Q

Why does the position of equilibrium move when the individual concentrations of elements are changed in a reaction?

A

To remove the change
(Reduce this concentration again)

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34
Q

In what type of reactions would the total pressure affect the position of equilibrium?

A

Gaseous reactions

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35
Q

How do we move the position of equilibrium if the pressure within a system is increased?

A

Moves it towards the side with the fewest GASEOUS molecules
(Compare the sum of the molecules - big numbers - on both sides)

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36
Q

What do we need to take notice of in order to move the position of equilibrium when the total pressure has changed?

A

The number of molecules on both sides of the equation (big numbers)

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37
Q

What does a greater number of gas molecules lead to?

A

A greater pressure

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38
Q

What leads to a greater pressure?

A

A greater number of gas molecules

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39
Q

Why do we move the position of equilibrium to the side containing the least molecules if the total pressure of a reaction has increased?

A

As it reduces the amount of molecules in a given volume (i.e - the pressure)

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40
Q

What is increasing the volume the same as doing?

A

Reducing the pressure

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41
Q

What is reducing the pressure the same as doing?

A

Increasing the volume

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42
Q

If the volume of a system is increased, what happens to the position of equilibrium and why?

A

It moves to the side containing the most molecules, as this will increase the pressure
(Increasing the volume is the same as reducing the pressure, so the system needs to try to increase it like this)

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43
Q

Enthalpy change symbol

A

ΔH

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44
Q

ΔH meaning

A

enthalpy change

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45
Q

What does the Enthalpy change show?

A

The value of energy of the forward reaction

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46
Q

Which reaction does the Enthalpy change always show the value of energy for?

A

Forward reaction

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47
Q

What does a negative Enthalpy change value represent?

A

An exothermic reaction

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48
Q

What does a positive Enthalpy change value represent?

A

An endothermic reaction

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49
Q

Exothermic reaction shown as the enthalpy change

A

Negative value

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50
Q

Endothermic reaction represented by the enthalpy change

A

Positive value

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51
Q

What do endothermic reactions do and what are they favoured by?

A

Absorb heat
favoured by increasing the temperature

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52
Q

What do exothermic reaction do and what are they favoured by?

A

Release heat
Favoured by decreasing the temperature

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53
Q

If the temperature increases in a reaction, what does the position of equilibrium do and why?

A

Moves it in the direction of the endothermic reaction to reduce it

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54
Q

Why does moving the position of equilibrium towards the endothermic reaction reduce the affect of the change in temperature when it’s increased?

A

During an endothermic reaction energy is transferred from the surroundings

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55
Q

How do you calculate the concentration of an acid if given its pH?

A

1- Concentration of H+ ions (protons)
2- Molar ratio

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56
Q

What type of acid is ethanoic acid?

A

Organic

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57
Q

Which acid is an organic acid?

A

ethanoic

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58
Q

What type of acids are sulphuric, hydrochloric and nitric acid?

A

Mineral/inorganic

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59
Q

Which acids are mineral/inorganic?

A

Sulphuric, hydrochloric and nitric acid

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60
Q

Electrolyte

A

A substance which will conduct electricity in an aqueous solution (or molten)

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61
Q

What does an electrolyte conduct electricity in?

A

Aqueous solution or molten

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62
Q

What can’t ions do in a solid?

A

Move

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63
Q

Strong electrolyte

A

Is largely dissociated into its ions in aqueous solution

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64
Q

What are largely dissociated into its ions in aqueous solution?

A

Strong electrolytes

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65
Q

Strong electrolytes examples

A

Soluble ionic compounds…
1. All salts which are soluble in water
2. Mineral/inorganic acids - sulphuric, hydrochloric and nitric acid
3. Alkalis such as sodium hydroxide

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66
Q

(Aq) meaning

A

Water molecules surrounding it

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67
Q

Dissociated

A

Split into its ions in solution

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68
Q

What’s the word for something being split into its ions in solution?

A

Dissociated

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69
Q

State symbol for water molecules completely surrounding something

A

(aq)

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70
Q

What is the % of electrolytes split into ions if they’re strong electrolytes? Why?

A

100%
Completely dissociated into its ions

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71
Q

Monophonic/monobasic

A

Releases 1 proton

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72
Q

Word for releases 1 proton

A

Monophonic/monobasic

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73
Q

Diprotic

A

Releases 2 protons

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74
Q

Word for releases 2 protons

A

Diprotic

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75
Q

Proton symbol

A

H+ (aq)

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76
Q

H+ (aq) meaning

A

Proton

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77
Q

What does every acid, strong or weak, give out?

A

Protons

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78
Q

What does every kind of itself give out protons?

A

Acids

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79
Q

Weak electrolyte

A

Is largely undissociated into its ions in aqueous solution - the degree of dissociation is often less than 1%

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80
Q

What’s the degree of dissociation for weak electrolytes?

A

Often less than 1%

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81
Q

What’s largely undissociated into its ions in aqueous solution?

A

Weak electrolytes

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82
Q

Examples of weak electrolytes

A
  1. Organic acids (e.g. - ethanoic acids)
  2. Ammonia (weak base)
  3. Water
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83
Q

What is ammonia?

A

A weak base

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84
Q

What does “weak” and “strong” refer to when discussing acids?

A

The amount of dissociation

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85
Q

Which phrases are used to describe the amount of dissociation in acids?

A

Weak or strong

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86
Q

Non-electrolytes

A

Do not conduct electricity and are not dissociated to any appreciable extent into ions in aqueous solution

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87
Q

What do not conduct electricity and aren’t dissociated to any appreciable extent into ion in aqueous solution?

A

Non-electrolytes

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88
Q

Examples of non-electrolytes

A
  1. Sugar
  2. Ethanol
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89
Q

Lowry-Bronsted theory

A

An acid is a substance which donates protons in aqueous solution
A base is a substance which accepts protons in aqueous solution

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90
Q

What is an acid? What is this based on?

A

A substance which donates protons in aqueous solution
Lowry-Bronsted theory

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91
Q

What is a base? What is this based on?

A

A substance which accepts protons in aqueous solution
Lowry-Bronsted theory

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92
Q

In what type of solution are protons accepted and donated with acids and bases?

A

Aqueous

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93
Q

What does an acid give out?

A

A base and a proton

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94
Q

Which substance donates protons in aqueous solution?

A

Acids

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95
Q

Which substance accepts protons in aqueous solution?

A

Bases

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96
Q

Can we permanently decide whether a chemical is an acid or a base?

A

No, only for that particular reaction in which is takes part

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97
Q

Describe strong acids and bases

A

Almost completely dissociated into their ions

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98
Q

Describe weak acids and bases

A

Largely undissociated into their ions in aqueous solution

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99
Q

What does the concentration of an acid refer to?

A

The amount of moles of acid present in a given volume

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100
Q

What is the amount of moles in a given volume if acid?

A

Its concentration

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101
Q

Concentrated acid

A

Large amount of moles of the acid present

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102
Q

Dilute acid

A

Small amount of moles of the acid present

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103
Q

What type of acid has a large amount of moles of the acid in it?

A

Concentrated

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104
Q

What type of acid has a small amount of moles of the acid present?

A

Dilute

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105
Q

What could be technically used as an indicator of acidic strength?

A

Ka - the acid dissociation constant

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106
Q

What can the acid dissociation constant be used as?

A

An indicator of acidic strength

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107
Q

What’s wrong with using the acid dissociation constant?

A

The numbers are difficult to handle

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108
Q

What’s easier to follow than using the acid dissociation constant to indicate acidic strength?

A

Hydrogen ion concentration expressed as pH

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109
Q

What is pH a measure of?

A

The [H+ (aq)] concentration

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110
Q

pH definition

A

-log10 [H+ (aq)]
(small 10)

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111
Q

What’s good about the pH scale?

A

A simple and widely applicable method to measuring the acidity, alkalinity or basicity of a substance in aqueous solution

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112
Q

What’s the pH scale used for?

A

Measuring the acidity of a substance in aqueous solution
Measuring the alkalinity or basicity of a substance in aqueous solution

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113
Q

What happens as the pH increases by 1 on the pH scale?

A

Concentration of H+ ions decreases by a factor of 10
(Lower pH —> higher concentration of H+ ions —> more acidic)

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114
Q

Relationship between the amount of H+ ions in an acid and its acidity

A

Low pH = higher concentration of H+ ions = more acidic

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115
Q

What’s the concentration of H+ ions in low pH levels and what does this mean?

A

High = more acidic

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116
Q

What can pH be measured using?

A

pH meter
Universal indicator

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117
Q

Positives of using a pH meter to measure pH

A

Accuracy - measures to within +-0.01 of a pH

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118
Q

Negatives of using a pH meter to measure pH

A

Often needs to be calibrated against a solution of known pH before use

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119
Q

Positives of using a universal indicator to measure pH

A

Paper or solution
Quick and cheap

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120
Q

Negatives of using a universal indicator to measure pH

A

Not especially accurate

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2
3
4
5
Perfectly
121
Q

What is a universal indicator ideal for measuring?

A

Soil pH

122
Q

What is pH dependant on?

A

Concentration and temperature of a substance

123
Q

What are pH values usually quoted on in terms of temperature?

A

25 degrees Celsius

124
Q

What can be done in terms of pH with strong acids and why?
Why can’t this be done with weak acids?

A

Can calculate the pH directly if the concentrations of the solutions are known - they’re assumed to be totally dissociated into their ions
Cannot be done so directly with weak acids - only a small fraction of the molecules are dissociated into ions

125
Q

Are negative pH’s possible?

A

Yes

126
Q

What’s the first thing to do when answering pH based questions?

A

Write down how it dissociates into its ions

127
Q

How do you calculate the pH of a substance from its concentration?

A
  1. Write down how it dissociates into its ions
  2. Molar ratio comparison between the starting reactant and the H+ ions
  3. Use the equation -log10[H+(aq)]
128
Q

How do you calculate the hydrogen ion concentration from pH values?

A

[H+] = 10^-pH

129
Q

Equation for calculating the hydrogen ion concentration of a substance

A

[H+] = 10^-pH

130
Q

Concentration shorthand

A

[ ]

131
Q

What does [ ] mean?

A

Concentration shorthand

132
Q

How do you calculate the concentration of an acid from its pH?

A
  1. Calculate the hydrogen ion concentration with [H+] = 10^-pH
  2. Molar ratio comparison between the acid and H+ ions
133
Q

How can equilibrium position be described in precise terms?

A

By combining the equilibrium concentrations to give the value of an equilibrium constant

134
Q

Equilibrium constant symbol

A

Kc

135
Q

What’s Kc?

A

The equilibrium constant

136
Q

What’s c in Kc (the equilibrium constant)?

A

Ratio of concentrations

137
Q

Equilibrium constant equation

A

Kc = [products]
——————
[reactants]

(Remember square brackets means concentration!)

138
Q

what are concentrations raised to the power of when calculating Kc?

A

The molar ratios

139
Q

What do we do with the molar ratios (big numbers) when calculating Kc?

A

Make them powers

140
Q

What do we do if there’s no unit for Kc?

A

Physically write “No unit”

141
Q

How do we work out the unit of Kc?

A

Remember the indices rule - dividing = minus
So, count the amount of moldm^-3 you have at the top and bottom and minus them
The answer goes to the mol section, and the dm’s original ^-3 is multiplied by this

142
Q

What do we do if we get the small number on top when calculating Kc’s unit?

A

Do the reciprocal…
Not moldm^-3 but
dm^-3mol-1

143
Q

If the value of Kc is larger than 1, what does this tell us?

A

More products than reactants in the equilibrium mixture - position of equilibrium lies to the right

144
Q

If the value of Kc is smaller than 1, what does this tell us?

A

More reactants than products in the equilibrium mixture - position of equilibrium lies to the left

145
Q

If the position of equilibrium lies to the left, what type of value would Kc be?

A

Smaller than 1

146
Q

If the position of equilibrium lies to the right, what type of value is Kc?

A

Larger than 1

147
Q

What can change the value of Kc? Why?

A

ONLY changes in temperature
The value of Kc is constant for a particular equilibrium reaction at constant temperature

148
Q

What is the value of Kc constant for?

A

A particular equilibrium reaction at constant temperature

149
Q

What doesn’t change Kc’s value? What do these do instead?

A

Concentration and pressure
Can only shift the position of equililbrium

150
Q

What can and can’t change the value of Kc?

A

Can - temperature
Can’t - concentration and pressure

151
Q

What does Kc give us information about?

A

Concentrations achieved at equilibrium

152
Q

What does Kc tell us nothing about?

A

How quickly equilibrium is reached

153
Q

When do we do a reciprocal with the units of Kc?

A

When the number on top is smaller than the bottom

154
Q

When we have an answer for the indices for the unit of Kc that’s bigger than 1 or zero, what do we do?

A

The answer goes to the mol
Multiply the answer with the original dm^-3

155
Q

If the values of Kc are all very similar in an experiment, can it be considered constant?

A

Yes, as there’s a margin for error with experimental data

156
Q

What’s it important to state if it’s included in the question in terms of equililbrium reactions?

A

The colour change

157
Q

When is a base called an alkali?

A

When dissolved in water

158
Q

What’s called an alkali if dissolved in water?

A

A base

159
Q

What do you call compounds or molecules that can act as both an acid and a base?

A

Amphoteric

160
Q

Amphoteric

A

A compound or a molecule that can act as both an acid and a base

161
Q

Where is ethanoic acid found?

A

In vinegar

162
Q

What type of acid does vinegar contain?

A

Ethanoic acid

163
Q

What forms with weak electrolytes and why?

A

An equilibrium as it only partly dissociates

164
Q

Which type of electrolyte forms equililbrium and why?

A

Weak, as if only partly dissociates

165
Q

What is Ka?

A

The acid dissociation constant

166
Q

How do you calculate the pH of an alkali?

A

14-(-log10 [OH-])

167
Q

What’s 14-(-log10[OH-]) for?

A

Calculating the pH of an alkali

168
Q

Are there protons involved in an base reaction?

A

A small amount, as the base dissolves in water

169
Q

Diprotic acid example

A

H2SO4 (sulphuric acid)

170
Q

What do we need to remember to do with Diprotic acids? Why?

A

Multiply their concentration by 2 in a pH calculation - they release 2 H+ ions per molecule

171
Q

Why do we need to multiply the concentration given by 2 when calculating pH of Diprotic acids?

A

They release 2 H+ ions per molecule

172
Q

What do Diprotic acids do?

A

Release 2 H+ ions per molecule

173
Q

What release 2 H+ ions per molecule?

A

Diprotic acids

174
Q

What actually are all of the examples of strong electrolytes?

A

Soluble ionic compounds

175
Q

What type of analysis is an acid base titration?

A

Volumetric

176
Q

What’s measured during an a acid-base titration?

A

The volume of one solution (e.g - acid) that reacts exactly with a known volume of another solution (e.g - a base)

177
Q

How do we measure the precise point of neutralisation using an acid-base titration?

A

Using an indicator

178
Q

What does an indicator help us do during an acid base titration?

A

Measure the precise point of neutralisation

179
Q

What are acid base titrations used for?

A

-The preparation of salts
-Measuring exact concentrations of acid or base solution

180
Q

What must we have in order to measure the exact concentration of an acid or base solution?

A

One of the solutions must have been standardized

181
Q

Why must one of the solutions be standardized during an acid base titration?

A

To measure EXACT concentrations of acid or base solution

182
Q

What’s a standard solution used for?

A

Finding out about the substances dissolved in the other solution

183
Q

What’s used to find out about a substance dissolved in the other solution?

A

A standard solution

184
Q

How is a standard solution made?

A

By dissolving an accurate mass of reactant into a known volume of water

185
Q

What does dissolving an accurate mass of reactant into a known volume of water give us?

A

A standard solution

186
Q

What does a standard solution give us?

A

An accurate concentration that can be used to work out the concentration of another solution that it reacts with

187
Q

What gives us an accurate concentration that can be used to work out the concentration of another solution that it reacts with during a titration?

A

A standard solution

188
Q

Features of a primary standard

A
  • High purity
    -Stability
    -Low hygroscopicity
    -High molar mass
189
Q

What are high purity, stability, low hydrgoscopicity and high molar mass all features of?

A

A primary standard

190
Q

Hygroscopicity

A

The tendency of a solid substance to absorb moisture from the surrounding atmosphere (e.g - CO2 and H2O)

191
Q

What’s the tendency of a solid substance to absorb moisture from the surrounding atmosphere?

A

Hydroscipicity

192
Q

What’s an example of a substance that cannot be used as a primary standard and why?

A

Sodium hydroxide
Reacts with atmospheric CO2

193
Q

What can’t sodium hydroxide be used as and why?

A

A primary standard - reacts with atmospheric CO2

194
Q

Give 2 examples of primary standards commonly used in Chemistry

A
  • Potassium hydrogen phthalate (KHP)
  • Sodium carbonate
195
Q

What are Potassium Hydrogen Phthalate (KHP) and Sodium Carbonate examples of?

A

Primary standards commonly used in Chemistry

196
Q

What’s potassium hydrogen phthalate (KHP) used for? Why?

A

The standardisation of aqueous base solutions
(It’s a stable acid, and its concentration doesn’t change over time)

197
Q

KHP

A

Potassium hydrogen phthalate

198
Q

Which primary standard is often used for the standardisation of aqueous base solutions and why?

A

Potassium hydrogen phthalate (KHP)
stable acid, concentration doesn’t change over time

199
Q

What’s sodium carbonate used for?

A

The standardisation of acid solutions

200
Q

Which primary standard is often used for the standardisation of acid solutions?

A

Sodium carbonate

201
Q

What’s the apparatus required for preparing a standard solution?

A

Volumetric flask
Funnel
Digital scales
Weighing bottle
Beaker
Glass rod

202
Q

How much standard solution does our method help us make?

A

250cm^3

203
Q

What’s the first step of preparing a standard solution?

A

Accurately weigh a known amount of the solid sample in a weighing bottle to 3d.p

204
Q

How many decimal places do we accurately weigh the known amount of solid sample for a standard solution?

A

3 d.p

205
Q

What do we do after we’ve accurately weighed our known amount of solid sample in a weighing bottle when preparing a standard solution?

A

Transfer all the solid into a 250cm^3 beaker then add no more than 150cm^3 distilled water and stir with a glass rod until the solid has completely dissolved

206
Q

Size of the beaker the solids are transferred into during an acid base titration

A

250cm^3

207
Q

How much distilled water do we add to the accurately weighed solid for a standard solution?

A

No more than 150cm^3

208
Q

What do we need to remember to do when transferring the contents of the beaker with the solids to the volumetric flask when preparing a standard solution? Why?

A

Don’t remove the glass rod when pouring - will lose ions

209
Q

Why shouldn’t we remove the glass rod when transferring contents from the beaker to the volumetric flask when preparing a standard solution?

A

We will lose ions

210
Q

How could we lose ions carelessly when preparing a standard solution?

A

Removing the glass rod when transferring form the beaker to the volumetric flask

211
Q

What do we do after dissolving the solid in distilled water when preparing a standard solution?

A

Use a funnel to transfer the contents of the beaker to a 250cm^3 volumetric flask

212
Q

How do we transfer the contents of the beaker to the volumetric flask when preparing a standard solution?

A

Using a funnel

213
Q

What’s the volume of the volumetric flask used when preparing a standard solution?

A

250cm^3

214
Q

What do we do after transferring the contents of the beaker to the volumetric flask when preparing a standard solution?

A

Rinse the beaker and glass rod thoroughly, at least 3 times, with distilled water and carefully pour the rinsings into the volumetric flask

215
Q

What do we need to rinse when preparing a standard solution?

A

The beaker and the glass rod

216
Q

What do we do with the rinsings of our beaker and glass rod when preparing a standard solution?

A

Pour them into the volumetric flask each time

217
Q

How many time do we rinse the beaker and glass rod when preparing a standard solution?

A

At least 3 times

218
Q

What do we do after rinsing the beaker and glass rod when preparing a standard solution?

A

Carefully add distilled water to the volumetric flask until the bottom of the meniscus is level with the horizontal line on the neck of the flask - the flask and graduation mark must be at eye level when the final drops are added using a Pasteur pipette

219
Q

How do we know how much distilled water to add to the volumetric flask when preparing a standard solution?

A

Add until the bottom of the meniscus is level with the horizontal line on the neck of the flask

220
Q

What must be at eye level when adding the final drops of distilled water to the volumetric flask when preparing a standard solution?

A

The flask and graduation mark

221
Q

How is the distilled water added to the volumetric flask when preparing a standard solution?

A

Using a Pasteur pipette

222
Q

What must the flask and graduation mark be at when adding the final drops of distilled water when preparing a standard solution?

A

At eye level

223
Q

What’s the final step of preparing a standard solution?

A

Holding the stopper into the neck of the flask, carefully turn the flask upside down several times to thoroughly mix the solution

224
Q

How do we thoroughly mix the solution when preparing a primary standard?

A

Hold the stopper into the neck of the flask, carefully turn the flask upside down several times

225
Q

What’s the apparatus required for performing a titration?

A

-Burette (+stand and clamp)
-Pipette
-Funnel
-Conical flask
-White tile

226
Q

What’s the volume of the pipette used during a titration?

A

25cm^3

227
Q

What’s the volume of the burette used during a titration?

A

50cm^3

228
Q

What’s the purpose of performing a titration?

A

To work out the concentration of an acid by titrating it against a standard solution of an alkali

229
Q

What’s the first step of performing a titration?

A

Using a funnel, pour a small volume of the acid into the burette to rinse it out

230
Q

What do we use to rinse out the burette?

A

Use a funnel to pour a small volume of acid in

231
Q

What do we do after rinsing out the burette when performing a titration?

A

Fill the burette with the acid using a funnel (make sure the jet is filled) and remove the funnel before recording the initial burette reading

232
Q

What do we use to fill up the burette with acid and what must we remember about it?

A

A funnel
Remember to remove it before recording the initial burette reading

233
Q

What do we do before recording the initial burette reading?

A

Remove the funnel

234
Q

What 2 things must we make sure before taking the initial burette reading when performing a titration?

A

-the funnel has been removed
-the jet is filled

235
Q

What do we do after recording the initial burette reading when performing a titration?

A

Rinse the volumetric pipette with a small volume of alkali solution

236
Q

What type of pipette is used during a titration?

A

Volumetric

237
Q

What’s the volumetric pipette rinsed with during a titration?

A

Alkali solution

238
Q

What’s the burette rinsed with during a titration?

A

Acid solution

239
Q

What do we do when performing a titration after rinsing the volumetric pipette with a small volume of alkali solution?

A

Accurately pipette 25cm^3 of alkali and place it into a conical flask

240
Q

How much alkali do we pipette with the volumetric pipette during a titration?

A

25cm^3

241
Q

Where do we place the alkali that we pipette with a volumetric pipette during a titration?

A

Into a conical flask

242
Q

What do we do after adding the alkali to the conical flask when performing a titration?

A

Add 2/3 drops of a suitable indicator

243
Q

How much indicator do we add when performing a titration?

A

2/3 drops

244
Q

Give 2 examples of suitable indicators for a titration

A

Phenolphthalein or methyl orange

245
Q

What are both phenolphthalein and methyl orange?

A

Indicators

246
Q

What do we do after adding the indicator to the alkali solution in a conical flask during a titration?

A

Open the tap on the burette to start adding the acid to the conical flask. Swirl the mixture continuously the mix it.

247
Q

How do we ensure that the acid from the burette and the alkali from the conical flask are mixing?

A

Swirl the mixture continuously

248
Q

What do we open to release the acid into the alkali in the conical flask during a titration?

A

The tap on the burette

249
Q

What does opening the tap on a burette do?

A

Release the acid to the alkali in the conical flask

250
Q

What do we do when the acid is being added to the alkali in the conical flask during a titration?

A

Whilst titrating the standard solution with the acid, the colour of the indicator will start to change. When this happens, slow down the flow of acid from the burette so that it is dripping into the conical flask one drop at a time.

251
Q

What do we do when the colour of the indicator starts to change during a titration?

A

Slow down the flow of acid from the burette so that it’s dripping into the conical flask 1 drop at a time

252
Q

What is the end point of a titration?

A

When 1 drop of acid indicator permanently changes the colour of the indicator

253
Q

What’s the point when 1 drop of acid will permanently change the colour of the indicator?

A

The end point

254
Q

What helps us see the end point of a titration? What is the end point?

A

A white tile, as it’s when 1 drop of acid will change the indicator colour permanently

255
Q

What do we do after the end point of a titration?

A

Record the volume of acid needed to neutralise the alkali
Subtracting the volume at the beginning from this gives us our titre

256
Q

How do we get our titre?

A

By subtracting the volume at the beginning from the volume at the end

257
Q

What does subtracting the volume of acid in the burette at the beginning from the volume needed at the end give us?

A

Our titre

258
Q

What’s the final step of performing a titration?

A

Rinse out the conical flask, top up the acid in the burette and repeat the steps to get 2 concordant results (within 0.2cm^3 of each other)

259
Q

How many times do we repeat the titration?

A

Until we get 2 concordant results (within 0.2cm^3 of each other)

260
Q

Concordant results (titration)

A

Within 0.2cm^3 of each other

261
Q

What do we call results that are within 0.2cm^3 of each other during a titration?

A

Concordant results

262
Q

Why can’t we use standard titration methods sometimes? What do we do instead?

A
  • Reaction between determined substance and titration can be too slow
  • Problems with the end point determination
  • Base could be an insoluble salt \

Use a back titration instead

263
Q

What would factors like the reaction between determined substance and titration being too slow, problems with the end point determination and a base being an insoluble salt lead to?

A

Not being able to use standard titration methods, and therefor have to use a back titration

264
Q

What happens during a back titration?

A

Known excess of one reagent A reacts with an unknown amount of reagent B, and at the end of the reaction, the amount of reagent A that remains is found by titration
A simple calculation gives the amount of reagent A that’s been used and the amount of reagent B that’s reacted

265
Q

Why is a back titration called a back titration?

A

Have to track back with calculations

266
Q

What are the steps of a back titration calculation?

A
  1. Write out acid/base titration reaction
  2. Calculate the moles of the thing you have concentration and volume of (usually the alkali) - from the titration!
  3. Use this to calculate the moles of the acid
  4. If only 25cm^3 used, but 250cm^3 batch made, must x10
  5. Calculate the original moles of acid (in excess from 1st reaction)
  6. Original moles (ans 5) minus moles left over from reaction (ans. 3 or 4) - gives the moles of acid that were used in the reaction
  7. Write out the original reaction (not the titration reaction)
  8. Use the moles that reacted (ans 6) and the ratio in the original reaction to calculate moles of whatever the acid is reacting with
  9. Use this to calculate the mass (m = n x M)
  10. Calculate the % (if required) —> mass calculated
    ———————— x100
    Original mass of object (e.g - tablet)
267
Q

How do you work out the moles of acid that were used in the reaction? (back titration)

A

Original amount of moles - moles left over from reaction (from titration)

268
Q

Why would you use a large conical flask for the back titration practical?

A

To prevent acid from escaping

269
Q

What do we do when calculating the mean titre?

A

-Don’t necessarily go for the last 3 titres
-Don’t include irregular values

270
Q

What are some possible reasons for incorrect titres? (5)

A

Errors while reading the burette
Difficult to see the indicator’s colour change
Jet not filled
Burette not rinsed beforehand
Funnel kept in burette

271
Q

What does including a rough titration affect for out results?

A

Their validity

272
Q

What affects the validity of titration results?

A

Including a rough titration

273
Q

How many times is the beaker and stirring rod rinsed when preparing a standard solution?

A

3 times

274
Q

To how many decimal places must we write ALL of the figures in a table for titrations?

A

2 d.p.

275
Q

Why do we add an excess of acid during a double titration?

A

Allows 100% of the solute to dissolve

276
Q

When does Kc’s value get larger?

A

When the reaction shifts right

277
Q

When does Kc’s value get smaller?

A

When the reaction shifts left

278
Q

What happens to Kc’s value when the reaction shifts right?

A

Gets larger

279
Q

What happens to Kc’s value when the reaction shifts left?

A

Gets smaller

280
Q

Is there a greater % error in measuring small or large volumes?

A

Greater % error in measuring small volumes

281
Q

When do we get the total error of a piece of equipment to multiply more than once? (Percentage error)

A

If used more than 1 piece of equipment, or the same one more than once

282
Q

Why might incorrect titres be obtained when completing a titration? (5)

A

-funnel kept in burette
-difficulty seeing the colour change of an indicator
-jet of burette not filled
-air bubble in burette
-equipment not rinsed with acid beforehand

283
Q

Why is equipment rinsed before use?

A

To remove SOLUBLE impurities

284
Q

Definition of a reversible reaction

A

Products react to form reactants and vice versa

285
Q

Products react to form reactants and vice versa

A

Reversible reaction

286
Q

How should a product be treated to obtain results for quantitative analysis?

A

Filtered
Washed to remove soluble impurities
Dried to a constant mass to ensure all water is removed

287
Q

Purpose of fluoride ions in drinking water

A

Strengthens teeth enamel
Decreases tooth decay

288
Q

How would we treat an ore to get ions in solution?

A

Add acid

289
Q

How would we obtain 0.050moldm-3 HCl from 2moldm-3 HCl?

A

Dilute by a factor of 40 (2/0.050)
Use pipette and volumetric flask

290
Q

What’s the purpose of filtering vs the purpose of washing a product of a reaction?

A

Filtering —> remove insoluble impurities
Wash —> remove soluble impurities

291
Q

What’s the only thing that can change the value of Kc?

A

Temperature

292
Q

What volume of solution do we always use in a pipette for a titration?

A

25cm^3

293
Q

When a Kc question says that the moles of 2 different things are the same, what do we do?

A

Use x squared

294
Q

To how many decimal places do we record titration values?

A

2

295
Q

What does preparing a standard solution give us?

A

An accurate concentration

296
Q

What happens if we don’t invert the flask after preparing a standard solution?

A

Fluctuations in the titration values

297
Q

What will be wrong with our titre is the jet of a burette isn’t full when performing a titration?

A

End point overshoot

298
Q

What effect will leaving the funnel in the burette have on the value of our titres?

A

Higher titres than expected

299
Q

Why do we need to rinse a burette with whatever were using in our titration before using it?

A

To remove traces of water that could dilute the titrant

300
Q

Why does not having the jet filled in a titration lead to an end point overshoot?

A

Acid used to fill the jet

A level Chemistry (39 decks)

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