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A-level Chemistry <3 > 5- Rates, Equalibrium, PH, Energy, Transition Elements > Flashcards

5- Rates, Equalibrium, PH, Energy, Transition Elements Flashcards

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1
Q

Oxidation is ….. of electrons

A

Loss

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2
Q

Reduction is …. Of electrons

A

Gain

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3
Q

What is a redox reaction

A

Reduction and oxidation happening simultaneously

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4
Q

What is an oxidising agent

A

Accepts electrons amd gets reduced

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5
Q

What is a reducing agent

A

Donates electrons and gets oxidised

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6
Q

What can be combined to make a full redox equation

A

An oxidation half equation can be combinded with a reduction half equation

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7
Q

What needs to be the same for half equations can be combined

A

The electrons

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8
Q

What are the only things your allowed to add to half equations

A

Electrons
H+
Water

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9
Q

What is the oxidation of iron, half equation
Fe2+ to Fe3+

A

Fe2+ —-> Fe3+ + e-

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10
Q

What is the reduction of manganateequation

A

MnO4- +8H+ +e- —> Mn2+ 4H2O

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11
Q

What elements are good at changing oxidation statex
And so therefore are good at what

A

Transition elements
This makes them usefull oxidising and reducing agents - as they readily give out and receive electrons

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12
Q

What colour is MnO4-

A

Purple

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13
Q

What is the colour change + why
Acidified potassium manganite (vll) redox

A

Purple to colourless
As the (Mn(H2O)4) 2+ Is colourless

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14
Q

What is the colour change + why
Acidified potassium dichromate redox

A

Orange
(Cr(h2o)6)3+ is violet (but usually looks green)
So a colour change looks orange to green

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15
Q

Tritations using transition element ions are what

A

Redox tritations

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16
Q

How to carry out a redox reaction
(Of manganite (vlll) ions)

A

first you measure out a quantity of the reducing agent eg.
aqueous Fe2+ ions, using a pipette, and put it in a conical flask

2 You then add some dilute sulfuric acid to the flask
- this is an excess, so you don’t have to be too exact.
(This acid is added to make sure there are plenty of H+ ions to allow the oxidising agent to be reduced)

  1. Now you gradually add the aqueous MnO4- (the oxidising agent) to the
    Reducing agent using a burette, swirling the conical flask as you do so.

You stop when the mixture in the flask just becomes tainted with the coloe
of the MnO4- and record the volume of the oxidising agent added

Run a few tritiations and then calculate the mean volume or MnO4-

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17
Q

T or f
In a redox tritiations
You add the known concentration to the substance of the unknown concentration

A

T

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18
Q

What can you do during a redox tritiations wot make the colour change Easier to spot

A

You could use a coloured reducing agent and a coloured oxidised agent - so you’d be looking for the moment the colour of the flask dissapears

Doing the reaction inffont of a white surface

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19
Q

Ensure you can do redox tritations calculations

A

👍

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20
Q

What is the definition of rate of reaction

A

The change in conc of reactants ( or products ) per unit time

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21
Q

What are the units of rates of reaction

A

Mol dm -3 s -1

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22
Q

What is activation energy

A

The minimum amount of energy a particle needs in order to react
The energy ( enthalpy) difference between the reactants and the transition state

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23
Q

What does rate of reaction describe

A

How quickly reancys are used up or how quick products are formed

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24
Q

What 2 diff rates can we look at when looking at rate of reaction;

A

The average rate for the entire reaction
Or
The rate at a specific point ( instantaneous rate )

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25
Q

What 4 ways can you measure rate

A

Vol of gas given of
Changes in PH (Ph probe )
Colour change ( use of colorimeter)
Loss of mass ( gas given off in an open system )

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26
Q

Make sure you know what the first, zero and second order graphs look like (6)

A

Check

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27
Q

What are the observations for the iodine/thiosulfate tritiations

A

CuI precipitation ( white)
Iodine - brown solution

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28
Q

What are the 3 main used of iodine / thiosulfate tritiations

A

Used to determine the clo- conctent in household bleach
Used to determine the cu2+ content in cu((ll) compound
Used to determine the cu content in copper alloy

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29
Q

In iodine / thiosulfate tritations
What are the oxidising agents oxidiseing

A

I- to I2

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30
Q

What is the iodine tritated against

A

Standard solution of sodium thiosulfate (S2O3 2- ion )

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31
Q

SO2O3 2-
In iodo thiosulfate tritations half equation goes to

A

S4O6 2-

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32
Q

What is the best way to balence the thiosulfate half equation

A

Look at charges not oxidation number

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33
Q

What is the molar ratio ot thiosulfate ion to iodide

A

2 : 1

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34
Q

What do you see in the iodine and thiosulfate tritations

A

Iodide -brown , fades to straw colour
When no iodine left colourless
( you can make this colour change easier to see by adding starch when it turns straw yellow)

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35
Q

What is rate of reaction usually measured in terms of

A

How fast the conc of One of the reactants is falling

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36
Q

T or f
Moles in the equation don’t effect the rate equation

A

T

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37
Q

What is rate of reaction proportional to

A

The rhe concentration of a particular reactant raised to a power

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38
Q

For each reactant in the rate equation
The power =

A

The order of reaction for that reactant

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39
Q

What orders are there in the rate equation

A

Zero
First
Second

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40
Q

How are orders determine in the rate equation

A

Experimentally

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41
Q

What is the overall order

A

The sum of the individual orders of reacts in the rate equation

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42
Q

Describe zero order

A

If the conc. changes, rate doesn’t change rate is proportional to [A]^0 = 1

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43
Q

Describe first order

A

Conc double, rate will double
Rate is proportion to [A]^1

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44
Q

Describe second order

A

Conc double, rate inc. by factor 2^2 = 4
Rate is proportional to [A]^2

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45
Q

What is K in the rate equation

A

Rate constant for a reaction

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46
Q

Is the rate constant differnt for differnt reactions

A

Yes

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47
Q

What are the units for the rate constant

A

The units depend on the order of the reaction

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48
Q

What is the value of the rate constant effected by

A

Temp
Presence / change of a catalyst

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49
Q

What does the rate equation provide lots of info about

A

The mechanism for the reaction

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50
Q

Iodine-sodium thiosulfate tritations are a way of finding the concentration of a …

A

Oxidising agent

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51
Q

How does iodine sodium thiosulfate work

A

STAGE 1: Use a sample of oxidising agent to oxidise as much iodide as possible.
1) Measure out a certain volume of potassium iodate(V) solution (KIO,) (the oxidising agent) - say 25.0 cm
2) Add this to an excess of acidified potassium iodide solution (KI).

STAGE 2: Find out how many moles of iodine have been produced.
You do this by titrating the resulting solution with sodium thiosulfate (Na,S,°s).
(You need to know the concentration of the sodium thiosulfate solution.)

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52
Q

How do you carry out the titration of iodine with sodium thiosulfate

A

1) Take the flask containing the solution that was produced in Stage 1.
2) form a burette add sodium thiosulfate solution to the flask drop by drop
3)It’s hard to see the end point, so when the iodine colour fades to a pale yellow (this is close to the end point), add 2 cm’ of starch solution (to detect the presence of iodine). The solution in the conical flask will go dark blue, showing there’s still some iodine there.
4) Add sodium thiosulfate one drop at a time until the blue colour disappears.
5) When this happens, it means all the iodine has just been reacted.
6) Now you can calculate the number of moles of iodine in the solution.

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53
Q

What is the reaction rate

A

The change in the amount of reactants or products per unit time

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54
Q

What are some ways to follow the rate of a reaction

A

Measure the volume of gas evolved
Measure the loss of mass as a gas is evolved
Use a colorimetry to measure the colour change of a reaction
Measure the ph change of a reaction

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55
Q

How can you find the rate from a concentration time graph

A

The rate at any point is given by the gradient at that point on the graph

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56
Q

How can you measure inital rates based on reactant concentration

A

1) carry out the reaction , continuously measuring one reactant
Use this to draw a concentration-time graph.
2) Repeat the experiment using a different initial concentration of the reactant
Repeat the experiment using a different initial concentration of the reactant.
Keet herations her eactats the same. Draw another concentration-time graph.
3) Use your graphs to calculate the initial rate for each experiment using the method above.
1) Repeat the proces for each reactant (different reactants may affect the rate differently).
5) Woulse on 19 how you can go on to look at how the different initial concentration safe ties

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57
Q

How can clock reactions be used to find inital rates

A

Clock Reactions not sea to Simplify the Initial Rate Method
The method described rathe & graphs. the last praction working out initial rates is a bit of a fat - Tob if measuring and drawing grapes, In clock reactions, the initial rate can beal stated.
1) In a clock reaction, you measure now the time taken for a set amount of produy to form changes as you vary the concentration of one of the reactants
There is usually an easily observable endpoint, such as a colour change, to tell you when the desired amount of product has formed.
3) The quicker the clock reaction finishes, the faster the initial rate of the reaction.
You need to make the following assumptions:
• The concentration of each reactant doesn’t change significantly over the time period of your clock reaction.
• The temperature stays constant.
• When the endpoint is seen, the reaction has not proceeded too far.
5) As long as these assumptions are reasonable for your experiment, you can assume that the rate of reaction stays constant during the time period of your measurement. So the rate of your clock reaction will be a good estimate for the initial rate of your reaction.

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58
Q

What is the iodine clock reaction

A

H,02 (ag) + 21(ag) + 2H1(ag) → 2H,00 + 12(00)
• A small amount of sodium thiosulfate solution and starch are added to an excess of hydrogen peroxide and iodide ions in acid solution.
(Starch is used as an indicator — it turns blue-black in the presence of iodine.)
• The sodium thiosulfate that is added to the reaction mixture reacts instantaneously with any iodine that forms:

2S2O32- + I2 —> 2I- + S4O62-
To begin with, all the iodine that forms in the first reaction is used up straight away in the second reaction But once all the sodium thiosulfate is used up, any more iodine that forms will stay in solution, so the starch indicator will suddenly turn the solution blue-black. This is the end of the clock reaction.
Varying iodide or hydrogen peroxide concentration while keeping the others constant will give different times for the colour change.

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59
Q

What does an order of reaction with respect to a particular reactant tell you

A

How the reactants concentration affects the rate

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60
Q

If you double the reactants concentration and the rate stays the same
What is the order

A

0

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61
Q

If you double the reactants concentration and the rate also doubles
What is the order

A

1

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62
Q

If you double the reactants concentration and the rate x4
What is the order

A

2

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63
Q

What is the reactions overall order

A

The sum of the orders of all the differnt reactants

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64
Q

What is rhe only way to find the orders of reaction

A

form experiment

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65
Q

What 2 ways experimentally can you find out orders of reactions

A

1) continuously monitor the change in concentration of A against time to construct a rate concentration graph
2) use an initial rates method to find out how the inital rate changes as you vary the concentration of A

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66
Q

How can you turn a concentration time graph to rate concentration graph

A

Find. The gradient at various points along the concentration time graph . This gives a set of points for the rate conc graph

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67
Q

What does rhe shape of a conc time graph or rate time graph show you

A

The order

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68
Q

What does a zero Order conc-time graph look like

A

Straight line down

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69
Q

What does a first order conc-time graph look like

A

Curved down

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70
Q

What does a zero order rate-conc graph look like

A

Horizontal line

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71
Q

What does the first order of the rate conc graph look like

A

Straight line through origin
Proportional

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72
Q

What does the second order rate- conc graph look like

A

A curve upwards

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73
Q

What does rhe rate equation tell you

A

How rate is affected by the concentrations of reactants

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74
Q

If the overall reaction is first order, then the rate constant is….
On a rate - conc graph of that reactant

A

Equal to the gradient

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75
Q

What is the half life of a reaction

A

The time is takes from half of the reactant to be used up

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76
Q

The half life of a first order reaction is …

A

Independent of the concentration
So each half life is rhe same length

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77
Q

What can the half life of a first order reaction be read off

A

It’s conc time graph by seeing how long it takes to halve the reactant concentration

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78
Q

What equation can you use if you know the half life of a first order reaction
To work out the rate constant

A

ln2
K = ——
t 1/2

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79
Q

Of all the half lives are equal what Order is it

A

1st

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80
Q

If a reaction has a series of steps, do all the steps have the same rate

A

No

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81
Q

If a reaction has a series of steps, what is the overall rate decided by, what is the called

A

The step with the slowest rate , the rate-determining step

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82
Q

The rate equation helps you work out the mechanism of a chemical reaction, to pick out wich reactions are involved in rate determining step
What are the rules:?

A
  • if a reactant appears in the rate equation, it must affect the rate, so this reactant, or so,etching derived for, it must be in the rate determining step
    -if the reactant isn’t in the rate equation it isn’t involved in the rate determine step at a
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83
Q

Can the rate determining step be anywhere in the mechanism

A

Yes

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84
Q

T or f
The reaction mechanism can usually be predicated from just the chemical equation

A

False they can’t usually

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85
Q

What does the order of a reaction with respect to a reactant show about the rate determining step

A

The number of molecules of that reaction wich are involved in the rate determining step

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86
Q

When nitrogen oxide and oxygen decompose
2N2O5 —> 4NO +O2
You may suggest that its second order with reseptors to n2o5
Yet expermenralt its found its first Oder with respect to n2o5.
What is a possible equation that fits with thus

A

N2O5 ——> NO2 + NO3 (rate determing step)
NO3 + N2O5 —-> 3NO2 + O2

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87
Q

Why do reactions oftern happen in a series of small change

A

Too complicated
Collisions with more than 2 species are unlikely

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88
Q

Chemical reacations only happen as fast as what ?

A

The slowest step

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89
Q

What is the slowest step called in a chemical reaction

A

Rate determining step

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90
Q

When you measure the rate of reaction what are you actually measuring

A

The rate determining step

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91
Q

What. Is a clue a mechanism is a multi step

A

Look at the stoichiomety in the rate eq and overall if they don’t match its most likely a multi step

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92
Q

What does the rate equation only show

A

Reacting species involved in the RDS

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93
Q

What does rhe order in the rate equation match in the RDS

A

The number of species

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94
Q

What is molecularity

A

Link between order and stochiometry

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95
Q

How does a temp increase effect K and how does it also effect rate

A

Inreases
Also increases

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96
Q

What is the Arrhenius equation for

A

Formula for temp dependence on the rate equation

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97
Q

What does rhe A stand for in the Arrhenius equation

A

A pre exponential factor

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98
Q

What does the pre exponential factor in the Arrhenius equation take I ot account

A

Frequency of collision
Orientation of molecules

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99
Q

What is activation in the Arrhenius equation measured in

A

J mol -1

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100
Q

What is temp measured in the Arrhenius equation

A

K

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101
Q

What does the R stand for in the Arrhenius equation

A

Ideal gas constant

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102
Q

What does the information after A in the Arrhenius equation equvioamt to

A

The number of molecules with energy above or equal to the activation energy

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103
Q

Do K and A in the Arrhenius equation have the same unit

A

Yes

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104
Q

Describe the link between K and Ea in the Arrhenius equation

A

If a reaction has a high Ea the. Rate of reaction is slow
Shown in the Arrhenius equation
- if Ea is high the fraction is larger so e raised to a larger negative value so K will have a smaller value so a slower rate

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105
Q

Describe the link between K andT in the Arrhenius equation

A

If reaction has high T rate is fast
Shown in the Arrhenius equation
If T is higher, denominator is larger so raising e to a smaller negative so K will have a
Larger value

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106
Q

How can the Arrhenius equation be expressed

A

lnK = - Ea/ RT + lnA

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107
Q

How can the natural log of the Arrhenius equation be written to be represent on a graph

A

LnK = - Ea/R x 1/T + lnA

LnA = C
1/T = x
-Ea/R = m
LnK = y

108
Q

A graphs for the Arrhenius equations shows a relationship between what

A

Rate constant
Temp

109
Q

What does the rate constant apply to

A

A particular reaction at a certain temperate

110
Q

When is a system said to be in dynamic equilibrium

A

The rate of th forward reaction is the same as the rate of the reverse reaction
(Conc are constant )

111
Q

When can a closed system only happen

A

In a closed system at a constant temperature

112
Q

Explain how bromine can set an equilibrium in a physical system

A

When liquid bromine is shaken in a closed flask, some of it changes to orange bromine gas, after a while, equilibrium is reached - bromine liquid is still changing to bromine gas and bromine gas is still changing to bromine liquid but they are changing at the same rate

113
Q

What does the equilibrium constant show

A

The ratio of products and reactants at dynamic equilibrium

114
Q

What is homogeneous equilibrium

A

All the reactants and products in a reaction are in the same state

115
Q

What are the heterogenous equilibrium

A

The reactants and products in a reaction are in differnt states

116
Q

If the mixture is homogenous what is put into the Kc expressions

A

All reactants and products are put into the expression

117
Q

If the mixture is heterogenous what is put into the Kc expression

A

Only he gazes and aqueous substances)
(Solids and liquids get left out)

118
Q

What is the exception for not including liquids or solid in heterogenous equilibrium in the Kc expression

A

If the solvent isn’t aqueous you need to include any water in the Kc expression

119
Q

Check example 1 /2 /3 on page 128 and 129

A
120
Q

Write
A(g) + 2B(g) = C(g)
In a Kp expression

A

p(C)
= —————-
p(A).p(B)^2

121
Q

Mole fraction equation

A

Number of moles of gas
————————————
Total number of moles of gas in gas mixture

122
Q

What should the sum of all mole fractions add up to

A

1

123
Q

What is partial pressure

A

The contribution that the gas makes towards the total pressure

124
Q

Partial pressure equation

A

Mole fraction X total pressure

125
Q

What should the sum of all partial pressures add up to

A

The total pressure

126
Q

What is the total pressure of a gas mixture

A

The sum of all the partial pressures of the individual gases

127
Q

Ensure you can work out partial pressure maths Qs

A
128
Q

What is a mole fraction

A

The proportion of a gas mixture that is a particular gas

129
Q

What changes for a Kp expression for heterogenous equilibrium

A

Don’t include solids or liquids

130
Q

The larger the value of Kc , what does this tell u about equilibrium

A

The equilibrium lies to the right , more products relative to reactants

131
Q

What is the only thing that effects the value of Kc and kp

A

Temperature

132
Q

Why doesn’t concentration changes effect Kc or kp

A

The value of the equilibrium is fixed at a given temperature
So if the conception of a one thing in the equilibrium mixture changes then the concentrations of the others must change to keep the value of Kc the same

133
Q

How does catalysts effect equilibrium

A

Approaches equlibrium faster
But has no effect on position or the value of Kc or kp

134
Q

How and why does temp effect K values

A

( if forward direction is exothermic)
K decreases with increasing temperature
Position of equilibrium, shifts to the left
More reactants, less products

If K decreases the system us no longer at equilibrium so the product reactant ratio must become smaller by the numerator decreasing and denominator increasing

135
Q

A + B = C
Explain what happening in terms of equilibrium and value of Kc
When A conc is increased

A

Increase denomination so ratio smaller, Kc can’t change so Poe shirt sright to favour C conc to also increase numerator and decrease A conc
So Kc stays constant

136
Q

When pressure increases what happens to the species partial pressures

A

All of them increase

137
Q

A + B = C
If pressure increases explain what happens to kp

A

Greater increase so expect kp to decrease by kp is uneffected
So Poe shits to right ( fewer moles) so p (c) inc and p( b) and p ( a ) decrease

138
Q

What are brønsted-Lowry acids

A

Release hydrogen ions when they are mixed with water

139
Q

You never get H+ ions by themselves in water
What are they always combined with to form what

A

H2O
To form hydroxonium ions, H3O+

140
Q

HA (aq) + H2O. —> ……

A

H3O+ (aq) + A- (aq)

141
Q

What are brønsted Lowry bases

A

Protons acceptors
When they’re in solution, they grab hydrogen ions form water

142
Q

(brønsted Lowry bases)
B(aq) + H2O(l) —>…?

A

BH+ (aq) + OH- (aq)

143
Q

how many protons can HCl and HNO3 release into solutions and what are they called

A

One protons
monobasic acids

144
Q

Give 2 examples of acids that release more than one proton

A

H2SO4
H3PO4

145
Q

Sulfuric acid releases …. Protons so it’s …..

A

2
Dibasic acid

146
Q

Phosphoric acid releases…. Protons so is called ….

A

3
tribasic

147
Q

Acids and bases form what ?

A

Conjugate pairs

148
Q

What are conjugate pairs

A

Species that are linked by the transfer of a proton.
They’re always on opposite sides of the reaction equation

149
Q

(Conjugate pairs)
The species that has lost a proton is the ……… and the species that has gained a proton is the ……….

A

Conjugate base
Conjugate acid

150
Q

when brønsted-Lowry acids and bases react together
Give a general Eq for it
And which ones are conjugate pairs

A

HA ( acid) + B ( base) = BH+ (acid) + A- (base)

HA and A- are conjugate pairs
And B and BH+

151
Q

HA ( acid) + B ( base) = BH+ (acid) + A- (base)
In the forward direction what donated a proton

A

HA acts as an acid and donated the proton

152
Q

HA ( acid) + B ( base) = BH+ (acid) + A- (base)
In the reverse reaction what accepts the proton

A

A- act as as a base and accepts a proton form the BH+ ion to from HA

153
Q

Why is water a special case when reaction with acids or bases

A

It reacts with acids to from a conjugate acid ( H3O+)
And reacts with a base to from a conjugate base ( OH-)

154
Q

Water + acid general Eq

A

HA (aq) + H2O = A- (aq) + H3O+ (aq)

155
Q

Water and base general Eq

A

B(aq) + H2O(l) = BH+ (aq) + OH- (aq)

156
Q

How do reactive metals react with acids

A

Release hydrogen gas
Metal atom donates electron to the H+ ions in the caud solution
The metal atoms are oxidised and the H+ ions are reduced

157
Q

What are alkalis

A

Bases that release hydroxide ions in water
They react with acids to form water

158
Q

Most insoluble bases are ….

A

Metal oxides

159
Q

Insoluble base + acid ionic Eq

A

2H+ (aq) + O^2- —> H2O (l)

160
Q

What did Lavoisier Belive about the acid base theory

A

Lavoisier thought it was all to do with oxygen…
Lavoisier came up with the first theory of acids and bases in the 18th century. He didn’t know the tormulas of compounds like hydrochloric acid but he did know that suluric acid had the formula H2SO4m and nitic acid had the formula HNO3,. So he proposed that acids had to have oxygen in them. It was later shown that acids like hydrochloric acid (HCl and hydragen sulfide (H2S) don’t have any oxygen in them at all.

161
Q

Who replaced Lavoisier acid base theory and with what

A

Arrhenius thought it was about H+and OH -…
Al the end of the 19th century, a chemist called Arrhenius suggested that acids release protons in aqueous solution, whilst bases release hydroxide ions. He said that when acids and bases react together they form water and a salt. This is true for loads of examples but doesn’t work for bases such as ammonia (NH3) which don’t contain any hydroxide ions.

162
Q

what theory did brønsted-Lowry come up with and who’s work was it based on

A

Brønsted and Lowry came up with their dietinition of acids and bases independently one another . It’s clearly based on Arrhenius theory, but broadens the direction of a base to be a proton acceptor. They also came up with the idea that acids and bases react to form conjugate pairs, rather than a salt and water. This definition currently explains most of our observations, so is one of the theories we still use today — around 100 years later

163
Q

Uses of acids

A

Industrial processes
(Fertilizer manufacture, dyes, drugs)

164
Q

Bases use

A

Household cleaning products, soap, manufacture of fertilisers

165
Q

Brønsted and Lowry
Deifnion of an acid

A

Proton donors

166
Q

Brønsted and Lowry
Deifnion of a base

A

Proton acceptors

167
Q

When an acid loose a H+ it becomes ….

A

A base

168
Q

When a basic substance gains a H+ it becomes …

A

An acid

169
Q

When an acid is present does a base need to be present

A

Yes

170
Q

What name is given to H3O+

A

Hydronium ion

171
Q

What is the definition for conjugate pairs

A

Conjugate acid - base pairs contains two species that can be interconnected by transfer of a proton

172
Q

What is another word for monoprotic

A

Monobasic

173
Q

The H+ ions from acids in water are often bonded to….

A

atoms that are electrgonetve ( o , f ,cl

174
Q

What is PH a measure of

A

How acidic or basic something is
Measures the concentration of hydrogen ions in solution

175
Q

Why is a logarithmic scale (PH scale) used

A

Conc of h ions can vary enormously

176
Q

PH = in terms of logs

A

-Log10[H+]

177
Q

What do you need to know to calculate the Ph of a solution

A

Hydrogen ion concentration

178
Q

If you know the PH of a solution, what can you find out and how

A

Hydrogen ion concentration
You need the inverse of the PH formula

179
Q

What is the inverse of the PH formula

A

[H+] = 10 ^-ph

180
Q

What does monobasic mean

A

One mole of acid produces one more of hydrogen ions

181
Q

Strong acids ionise fully in solution ( eg, hcl) and is monobasic. What does this mean for the H+ conc

A

The same as the acid concentration

182
Q

For 0.1 mole dm -3 of HCl
What is the conc of H+

A

Also 0.1

183
Q

Water dissociates into hydroxonium ions and hydroxide ions
How is this more simply written

A

H20 = H+ + OH-

184
Q

The equilibrium constant for the dissociation of water is called what …
And what is the simple

A

The ionic product of water
Kw

185
Q

What are the units of Kw always

A

Mol^2dm^-6

186
Q

Does it matter whether water is pure of part of a solution for the Kw constant

A

No , this equlibrium constant is always happening

187
Q

What is the Kw expression

A

Kw = [H+][OH-]

188
Q

For pure water what is the ratio of H+ and OH- due to it’s dissociation

A

1:1

189
Q

For pure what what can Kw also be written as and why

A

[H+]= [OH-]
So
Kw = [H+]^2

190
Q

If you know Kw of pure water at a certain temp, what can you calculate

A

[H+] which can be used to find PH

191
Q

How does changing conc of either [H+] or [OH-] effect Kw

A

The value of Kw doesn’t change, as the equilibrium will shift, changing concentration of the other substances to keep the value of Kc the same

192
Q

How does changing temp of solution change the value of Kw

A

The dissociation of water is an endothermic process, so for example, warming the solution shifts the equilibrium to the right and Kw increase

193
Q

T or f
Kw always have the same value of pure water of aq solution at a given temp

A

T

194
Q

What happens to NaOH and KOH in water

A

They are strong bases that fully ionise in water

195
Q

NaOH and KOH donates …… per mole of base
What does the mean for the link between conc of base and oh-

A

One mole of OH- ions
They have the same conc

196
Q

How do you work out PH for, known base conc

A

Base conc gives OH- conc
OH- conc links to H+ conc with Kw
h+ gives PH

197
Q

What the PH formula

A

-Log[H+]

198
Q

What the rearranged ph formula to find H+ conc

A

[H+] = 10^-Ph

199
Q

How many dp should you give Ph to

A

2

200
Q

What happens to PH when diluting strong acids

A

The same number H+ ions in a larger volume of solution
Conc dec, so PH inc

201
Q

Where does the equilibrium lie of the dissociation of weak acids

A

The left

202
Q

What is the general Ka equation

A

[H+] [A]
Ka= ———————-
[HA]

203
Q

Unit for Ka

A

In mol dm - 3

204
Q

How does Ka change in respects to the strength of an acid

A

Increases the stronger the acid
As dissociated more so more H+ so the numerator in the expression increases so an increase in Ka

205
Q

If tempt increases what happens to Ka
And why

A

Increases
As equilibrium shifts right ( it’s an endothermic reaction)

206
Q

What 2 assumptions are made to use the Ka expression

A

[Ha] inital = [HA]equilibrium

[H+] = [A-]

207
Q

When is [H+] = [A-] assumption valid

A

Of there are no other reactants added

208
Q

Why does [Ha] inital = [HA]equilibrium work

A

Very little dissociation

209
Q

When is this less reliable

[Ha] inital = [HA]equilibrium

A

The stronger the acid the less reliable the assumption

210
Q

[H+]= [A-]
What is this ignoring

A

H+ from water

211
Q

Why is pKA used

A

As the value of Ka for weak acids is almost always very small
So to create a more usable scale pKA is used

212
Q

pKa =
Formula

A

-log Ka

213
Q

Ka = …
Formula

A

10^-pka

214
Q

pKa units

A

None

215
Q

The weaker the acid the….. the value of pKA

A

Larger

216
Q

Why is [H+] not the same conc as the acid when it is a weak acid

A

The weak acids down fully ionise in solutions

217
Q

What constant do you use for ph of a weak acid

A

Ka

218
Q

What does Ka apply to

A

A particular acid at a specific temperature regardless of concentration

219
Q

Be able to use Kpa , Ka, H+ and Ph to calculate weak and strong acids

A
220
Q

Is the dissociation of water exo or endo

A

Endo

221
Q

What does Kc[H2O] =

A

Kw

222
Q

Kw expression

A

Kw = [H+] [OH-]

223
Q

In pure water what assumption can you make

A

[H+] = [OH-]

224
Q

What is the PH of pure water at rtmp

A

7

225
Q

What does Kw=
Simplified

A

[H+] ^2

226
Q

What is the Kw value for pure water at rtmp

A

1x10^-14
Mol2dm^-3

227
Q

What do all aqueous solutions contain

A

H+
OH-

228
Q

In pure water and neutral solutions
What is the link between H+ and OH-

A

They are equal

229
Q

In acidic solutions

What is the link between H+ and OH-

A

[H+] > [OH-]

230
Q

In alkaline solutions
What is the link between H+ and OH-

A

[H+] < [OH-]

231
Q

What is another way of writting the dissociation to water

A

2H20 = H3+0. + OH-

232
Q

What happens to Ph of water as temp increases and why

A

Dissociation of water is endothermic so increasing the temp would push Poe to the right
Inc Kw, inc H+ ions and so lowering PH

233
Q

If temp increases, PH decreaes
How is water still neutral

A

As OH- have also increased
Neural solution is defined as equal number of moles of H+ and OH- not ph of 7

234
Q

What is strength of a base measured on

A

Dissociation in solution to Oh- ions

235
Q

Show NH3 is a weak base

A

NH3 + H2O = NH4+. + OH-

236
Q

Ensure you can calc PH around strong bases
What key info do you need

A

Kw
—- = [H+]
[oh-]

237
Q

How to work out neutralisation PH Qs

A

Balenced Q
Starting moles
Find limiting reactant
Find final moles
Find new vol
Find concentration
Multiply to account for it being monoptoric or disprotic
chmage to H+ if in OH-
The PH

238
Q

What is a buffer

A

A solution that is able to resist changes in PHwhem small volumes of acids and bases are added

239
Q

Uses of buffers

A

1) store enzymes which change shape if PH changes too much
2) soap in shampoo raide the ph and cause skin irritation so buffers are used
3) induturial dye processes and manufacture of pharmaceuticals are controlled using buffers
4) baby lotion is buffered to inhibit growth of bacteria which can cause nappy rash

240
Q

Why does blood contain buffers

A

Exersize releases Latic acud
Blood should stay between 7.35 and 7.45 so buffered to keep in range

241
Q

What is buffered formed form

A

1) an acud and its salt
2) excess weak acid and a strong base with partial nutrilaisation

242
Q

What must buffers contain

A

HA
A-
(Weak acid and conjugate base)

243
Q

Why can’t a strong acud be used when making a buffer

A

It completly dissociates so no HA

244
Q

Why can’t you use a weak acid alone when making a buffer

A

Only slightly dissociates so not high enough A-

245
Q

Use 2 equations to show how buffers are made form acid and corresponding salt

A

1) CH3COOH = CH3OO- + H+
this only partially dissociates so leaving a high reserve of HA ( CH3COOH)

2) CH3COO-NA+ —> CH3COO- + NA+
The ch3coo- is in reservoir as the salt fully dissociates

246
Q

How do buffers work when H+ ions are added

A

System opposes the change as POE shifts left to lower H+
There is a reservoir of A- to react with so HA increases

247
Q

How do buffers work when OH- are added

A

They react with H+ ion to make water , the system opposes the change by POE shifts right to restore H+
There is a reservoir of HA so can dissociates into H+

248
Q

How to make a buffer from partial neutralisation (use Eq)

A

Weak acid and strong base
CH3COOH + NAOH —> CH3COO-NA+ + H2O
as a general rule add half amount of moles of bases as you add to ensure partial neutralisation

This means CH3COOH left ( leave a reservoir of HA)

The product CH3COO-NA+ which dissociates into CH3COO- which is in reservoirs

249
Q

when dealing with buffers do we assume
[H+] = [A-]

A

No that wouldn’t be a buffer

250
Q

When are buffers most effective

A

When [HA] = [A-]

251
Q

Ka for buffers with assumption

A

Ka = H+

252
Q

What is the pKA of buffer

A

PKA = PH

253
Q

What does buffers operate over

A

2 PH units centred at pKa

254
Q

rearrange Ka
To make H+ subject

A

= Ka [HA] / [A-]

255
Q

What is a buffer

A

Solution that minimises changes in OH when small amounts of acid or base are added

256
Q

Do. Buffers stop PH from changing

A

No , it makes the change very slight

257
Q

Buffers only work for what

A

Small amounts of acid or base.
Too much and they won’t be able to cope

258
Q

What are the types of buffers you can get

A

Acidic
Basic

259
Q

What equilibrium is set up for an acidic buffer no matter how it’s made
( ethanoic acid as an example)

A

CH3COOH = H+ + CH3COO-

260
Q

What does an acidic buffer equilibrium system contain

A

lots of undissociated HA
Lots of the acids conjunctive base A-
enough H + ion to make the solution acidic

261
Q

How is thePH of the blood controlled

A

using a carbonic acid-hydrogen carbonate buffer system

262
Q

What two equilibrium reactions occur in blood

A

H2CO3 = H+ + HCO3-
H2CO3 = H2O (l) + CO2

263
Q

what PH does blood need to kept between

A

7.35 and 7.45

264
Q

How are the levels of H2CO3 controlled in blood

A

Respiration
When breathing Out CO2 the H2CO3 is reduced as it moves the equilibrium to the right

265
Q

What are the levels of HCO3- controlled by in the blood

A

By the kidneys wich excess being excreted in urine

266
Q

When calculation PH of acidic buffer s
What assumptions can you make

A

1) the salt of the conjucgate base is fully dissociates so we assume the equilibrium conc of A- us the same as Initial conc of the salt
2) HA is only slightly dissociated, so assume that it’d equilibrium conc is the same as its initial conc

267
Q

Ensure you can do buffer calls

A

A-level Chemistry <3 (9 decks)

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