Module 5: Rates, Equilibrium And PH Flashcards
Rate of reaction
What 4 ways can you measure rate of reaction
Gas collection
Mass loss
Disappearing cross
Colorimeter
Rate of reaction
Two ways to measure gas collection
Over water
Gas syringe
Rate of reaction
Negative of sometimes using gas collection over water
Some gases can dissolve in water
Rate of reaction
What is used to measure rate in mass loss
Mass balance and loss of mass recorded
Rate of reaction
How is disappearing cross done for measuring rate
As solid forms increasing turbidity and can’t see cross
Rate of reaction
How is colorimeter used to measure rate
Measures changes in colour through amount of light absorbed
Orders of reaction
What are orders used for
Finding which reactant impacts rate the most
Orders of reaction
How are orders found
Change conc of each reactant independently
Orders of reaction
What may happen as you increase concentration of any one reactant
May increase rate
May have no effect
Orders of reaction
What is rate always proportional to
Change in concentration of a particular reactant
Orders of reaction
Symbols for proportionality
Rate § [reactant]^x
Orders of reaction
What are the most common orders
Zero order, first order, second order
Orders of reaction
What is the power when zero order
0
Orders of reaction
What does a zero order with respect to the reactant mean
Concentration of a reactant has no effect on the rate
Orders of reaction
Why does zero order mean not influences rate
Any thing to power of 0 = 1
Orders of reaction
What is the power (x) in first order
1
Orders of reaction
What is first order with respect to the reactant
When rate depends on conc raised to power of 1
(Directly proportional )
Orders of reaction
In first order if conc of a is doubled whayt happens to rate
Rate increases by a factor of 2^1 = 2
Orders of reaction
What is power (x) in second order
2
Orders of reaction
What’s second order
When rate depend on it’s reaction raised to the power of two
Orders of reaction
In a second order reaction what happens if the conc of a is doubles
Reaction rate increases by factors of 2^2 = 4
Orders of reaction
Proportional symbols for zero order
Rate § [A]^0
Orders of reaction
Proportional symbols for first order
Rate § [A]^1
Orders of reaction
Proportional symbols for second order
Rate § [A] ^2
Orders of reaction
How to find order of a reactant from table
Find multiplier difference in conc of reactant
Find multiplier difference in rate
Find relationship between multiplier, becomes order
Orders of reaction
What does the rate equation give
Mathematical relationship between the conc of reactants and the reaction rates
Orders of reaction
What would the rate equation for reactants A and B be
Rate = k [A]^m [B]^n
Orders of reaction
What is the rate constant k in the rate equation
Proportionality constant
Number that mathematically converts between rate of reactions and concentration and orders
Orders of reaction
What is the overall order of reaction
Gives overall effect of the concentrations of all the reactants
Orders of reaction
How is the overall order calculated
Sum of orders with respect to each reactant
Orders of reaction
What is the overall order for equation rate = k [A]^m [B]^n
Overall order = m + n
Orders of reaction
How do you find the rate constant k
Rearrange equation to make k the constant
Substitute values of concentration and initial rate and solve
Orders of reaction
What does the units of rate constant k depend on
Number of concentration terms in rate equation
Orders of reaction
How do you work out units of rate constant k
Rearrange to make k subject
Substitute units into expression
Simplify
Orders of reaction
What is the units of rate
Mol dm^-3 s^-1
Concentration time graphs
How can rate be measures from colour change
Using colorimeter
Concentration time graphs
How does colorimeter measure change in colour
Wavelength of light passing through coloured solution is controlled using filter and amount of light absorbed is measured
Concentration time graphs
What is the gradient for concentration time graph
Rate of reaction
Concentration time graphs
How can the order with respect to a reactant be deduced from these graphs
The shape
Concentration time graphs
What shape is conc time graph for a zero order reaction
Straight line with negative gradient
Concentration time graphs
Why is a zeri order reaction linear negative
Reaction rate(gradient) does not change throughout
Concentration time graphs
What is shape of a first order reaction
Downward curve with decreasing gradient over time
Concentration time graphs
Why is first order reaction graph downward curve shaped
As gradient (rate) decreases with time reaction slows down
Concentration time graphs
What is a half life
Time taken for the conc of a reactant to half its original value
Concentration time graphs
Shape of a second order graph
Steeper downward curve tailing off more slowly (will not be expected to analysis)
Concentration time graphs
What is true of the half life for a first order reaction
Will be constant
Concentration time graphs
Symbol for half life
t1/2 (small 1/2)
Concentration time graphs
What is the pattern of constant half life called
Exponential decay
Concentration time graphs
Do the half lives have to be concurrent to be constant and first order
No
Concentration time graphs
What are type two ways to calculate k for first order reaction
Using rate equation
Using Half life
Concentration time graphs
How to calculate k in first order reaction from graph
Find rate at specific point with tangent
Use rate and concentration at same point to find k using rate equation
Concentration time graphs
What is equation for finding k using half life
K= ln 2 / t1/2
Rate Concentration graphs
Why are they important
Offer route into direct link between rate and concentration in rate equation
Rate Concentration graphs
What can be shown by shape of graph
Order with respect to a reactant
Rate Concentration graphs
Shape of zero order graph
horizontal straight line with zero gradient
Rate Concentration graphs
Rate equation for zero order
Rate=k
Rate Concentration graphs
What is the y intercept on zero order graph
Rate constant k
Rate Concentration graphs
Why is zero order graph a horizontal line
Rate does not change with increasing conc
Rate Concentration graphs
What is shape of first order graph
Straight line graph with positive gradient through origin
Rate Concentration graphs
Rate equation of first order graph with respect to a
Rate = k [A]
Rate Concentration graphs
Why is first order that shape
Rate directly proportional to concentration
Rate Concentration graphs
How can rate constant k be determined for first order graph
Measuring gradient
Rate Concentration graphs
What shape is a second Oder graph
Upward curve with increasing gradient through origin
Rate Concentration graphs
Rate equation with respect to a
Rate = k[A]^2
Rate Concentration graphs
Can k be calculated from second order graph
No
Rate Concentration graphs
What can be done to find k from a second order graph
Plot another graph with rate against concentration squared and should be straight line through origin with gradient being k
Rate determining step
What is a rate determining step
In reaction with multiple step[s its the slowest step
Rate determining step
How is rds linked to rate equation
All of reactant involved in slowest step and steps before are in rate equation
Rate determining step
Why is it unlikely some reactions happen in one step
Reactants unlikely to colllide correctly if lots eg one molecule h2o2 two I- ions and two H+ ions
Rate determining step
What is more likely for a reaction like this
Take place in a series of steps
Rate determining step
What is the series of steps that makes up an overall reaction called
Reaction mechanism
Rate determining step
What two things have to be for a reaction mechanism to be correct
Rate equation only included reacting involved in the rate determining steps and reactions before
Orders in rate equation match number of species involved in the rate determining step
Rate determining step
Can rds be predicted from just overall equation
No not normally
Rate determining step
Is the RDS always the first step
No
Arrhenius equation
is the equation given
yes on data sheet
Arrhenius equation
what is the raw equation
k=A x e^-Ea/RT
Arrhenius equation
what is the ln equation
ln k = -Ea/RT + ln A
Arrhenius equation
wgat is k and units
rate constant
units dependent on rate eq
Arrhenius equation
what is A and units
pre exponential factor
units dependent on rate eq
links proportionality
Arrhenius equation
what is e
e is e
mathematical function
Arrhenius equation
what is Ea and units
activation energy
J mol^-1
Arrhenius equation
what is R and units
gas constant
8.314 J mol^-1 K^-1
on data sheet
Arrhenius equation
what is T and units
temperature
K
Arrhenius equation
how to change C to K
+273
Arrhenius equation
how to change kJ mol^-1 to J mol^-1
x 1000
Arrhenius equation
what does increasing T do to k and why
increasing T increases k
more particles have E>Ea
increases exponential
Arrhenius equation
what does increasing Ea do to k
increasing Ea decreases k
less particles have E>Ea
decreases exponential
Arrhenius equation
what does a bigger rate constant mean
faster rate of reaction
Arrhenius equation
what does the natural log form of the equation equate to
equation of straight lie graph y=mx+c
Arrhenius equation
what is x axis of natural log eq graph
1/T
Arrhenius equation
what is the y axis of the natural log eq graph
ln k
Arrhenius equation
what is the gradient on ln eq graph
-Ea/R
Arrhenius equation
what is the y intercept on ln eq graph
ln A
Arrhenius equation
what can be found by plotting a graph of ln k versus 1/T
activatio. energy Ea and Arrhenius constant A
Arrhenius equation
why does changing the temperature change the rate constant
according to rate equation, rate depends only on rate constant and reactant concentrations
Arrhenius equation when does k apply
to particular reaction at certain temperature
Equilibrium
What is K
Equilibrium constant
Equilibrium
What is Kc
Equilibrium constant with respect to concentration
Equilibrium
What is Kp
Equilibrium constant with respect to pressure
Equilibrium
What is pressure measured in
Pa/kPa/MPa/atm
Equilibrium
What is mole fraction
Proportion of gas compared to total number of miles in the gas mixture
Equilibrium
How do you work out mole fraction
Number of moles of particular gas/ total number of moles
Equilibrium
What is partial pressure
Proportion of total pressure that a particular gas contributes to
Equilibrium
What symbol is partia;l pressure
p
Equilibrium
How do you work out partial pressure
Mol fraction x total pressure
Equilibrium
What does a rice table stand for
Reaction
Initial
Change
Equilibrium
Equilibrium
How is a rice table applied to Kp
Same as Kc but use moles
Equilibrium
What do you do after found moles at equilibrium In rice table
Covert each to mol fraction then partial pressures
Equilibrium
What do you do with partial; pressures to find Kp
Substitute into Kp expression
Equilibrium
What are the units for Kp
Change according to number of pressure terms
Equilibrium
In exam what do u do if there are no units
Write unit less
Equilibrium
What is the equilibrium law
Ratio of products to react at raised to power of molar ratio remains a constant at a given temperature
Equilibrium
What does the equilibrium constant represent
Where position of equilibrium is
Equilibrium
What does a K value of more than 1 signify
More towards products /right
Equilibrium
What does a K value of less than 1 signify
More towards products /left
Equilibrium
What does a K value of 1 signify
Positions of equilibrium directly in centre
Equilibrium
What factprs can alter then value of K
Temperature ONLY
Equilibrium
What factors don’t affect value of K
Conc pressure catalyst
Equilibrium
What is a homogenous reaction
All products and reactants are in same state
Equilibrium
What is a heterogenous reaction
Reactants and products are in different states
Equilibrium
What do you include in the equilibrium constant if a home goes reaction
All reactants and products
Equilibrium
What do you put into equilibrium constant if heterogenous reaction
Only gas and aqueous substances and leave out any solids or liquids
Equilibrium
What is the exception for heterogenous reactions equilibrium constant
If solvent isn’t aqueous need to include any water
Equilibrium
What is the total pressure if a gas mixture
Sum of all partial pressures of individual gases
Equilibrium
What do all mole fractions add to
1
Equilibrium
What do partial pressures add to
Equilibrium
Why is there no square brackets for Kp
Because they’re partial pressures not concentration
Equilibrium
How do you write partial pressure of N2
p(N2)
Equilibrium
What do you include if writing Kp for a heterogenous equilibrium
Only include gases not liquids or solids
Equilibrium
What happens to value of Kp if increase temperature of an exothermic forward reaction
As. POE shifts to left then less product is formed and if less product numerator decreases and therefor Kp decreases
Equilibrium
Why does only temperature change value of K
Definition of K is given at a certain temp
Equilibrium
What does changing the pressure and concentration affect
Shifts the position of equilibrium to counter the change to keep the values of K the same
Equilibrium
What does changing the temperature affect
Alters amount of reactants and products at equilibrium and also value of K
Equilibrium
What affects do catalysts have
No effect on POE or value of K
Can’t increase yield but just mean equilibrium is approached faster
Acids and bases
What is a Bronsted-Lowry acid
Species that can donate a proton
Acids and bases
What is a bronsted lowery base
Species that can accept a proton
Acids and bases
What does amphoteric mean
Can act as either acid or base
Acids and bases
What do H+ ions always combine with in water
HA(aq) + H2O(l) —> H3O+(aq) + OH-(aq)
Acids and bases
What do bases do I water
B(aq) + H2O —> BH+(aq) + OH-
Acids and bases
What are monoprotic acids
Only have one proton they can release into solution
Acids and bases
What is a diprotic acid
Release 2 protons in solution
Acids and bases
Dissociation equation for sulfuric acid
H2SO4(aq) <==> 2H+ (aq) + SO4^2-(aq)
Acids and bases
What is a triprotic acid
Can release 3 protons in solution
Acids and bases what are conjugate pairs
Linked by the transfer of a proton
Acids and bases
Where are conjugate pairs always on an equation
Opposites sides of the reaction
Acids and bases
What is the conjugate base pair
Lost a proton
Acids and bases
What is a conjugate acid
Gained a proton
Acids and bases
How do you label conjugate acid base pairs
Acid 1 + base 1 —> acid 2 + base 2
Acids and bases
What is a bronsted Lowry acid base reaction
Reaction involving transfer of a proton
Acids and bases
Ionic equation for metal and acid (Ca)
Ca(s) + 2H+(aq) —>Ca2+ (aq) + H2(aq)
Acids and bases
Ionic equation for acid and carbonate
CO3 ^2-(aq) +2 H+ (aq) —> H2O (l) + CO2 (g)
Acids and bases
Ionic equation for acid and alkali
H+(aq) + OH-(aq) —>H2O(l)
Acids and bases
Ionic equation. For acid and oxide
2H+ (aq) + O^2-(s) —> H2O(l)
Acids and bases
What three stages important in development in acid base theory
Lavoisier
Arrhenius
Bronsted Lowry
Acids and bases
What did Lavoisier do
Didn’t have many formulas but knew sulfuric and nitric so proposed all acids have oxygen in them but later disproved
Acids and bases
What did Arrhenius do
Suggested acids release H+ in solution and bases OH- and reacted to form water and salt
Works for most but some not eg ammonia
Acids and bases
What did bronsted and lowery
Worked more on arrenhius came up with modern definitions which could explain observations
pH
What is pH a measure of
How acidic or basic something is by measuring hydrogen ion concentration
Acids and bases pH
What dies the pH scale use
A logarithmic scale
Acids and bases pH
What does it mean when solution si neutral (2)
pH 7
Or [H+]=[OH-]
Acids and bases pH
What is the equation for pH
pH=-log[H+]
Acids and bases pH
What is pH range
0(very acidic
14(very basic
Acids and bases pH
Equation for conc of hydrogen ions
[H+]= 10^-pH
pH strong acids
What do strong acids do in solution
Fully ionise in solution
pH strong acids
What si [H+] the same as
Conc of a strong acid
pH strong acids
What do you do for conc of strong acid if given [H+] but diprotic
Divide by 2 ad each released two protons
pH for strong acid
How do u do strong acid ph dilution calc
Find moles in original then find conc in new dilly open volume
Kw
What is Kw
Ionic product of water
Kw
What is the dissociation of water equation
H2O <==> H+ + OH-
Kw
Kc expression for dissociation of water
[H+][OH-]/[H2O]
Kw
Where does positions of equilibrium lay in dissociation of water and why
Very far to left as percentage which dissociates is very small
Kw
What does th POE being so far to the left mean for concentration of H2O
Remains constant before equilibrium and after
Kw
So what is Kw mathematically
Kw=Kc[H2O]
Kw
What is the expression for Kw
Kw=[H+][OH-]
Kw
What is the units for Kw
Mol^2 Dm^-6
Kw
What is the value of Kw and where can u find t
1 x 10^-14
In data sheet
Kw
How do you prove the pH of pure water is 7
Kw=[H+][OH-]
Assume [H+]=[OH-]
1 x 10^-14=[H+]^2
[H+]=1 x 10^-7
pH= -log(1 x 10^-7) = 7
Kw
As temp rises pH of water decreases is the water now acidic alkaline or still neutral
Solution is neutral as [H+]=[OH-] still
Kw
Is the ionisation of water endothermic or exothermic
Endothermic
Kw
Explain why the ionisation water is endothermic in terms of Kw
As temp increases, Kw increases, more towards products, POE more to right and temp increase favours endothermic
Kw
What does water actually dissociate into
2 H2O (l) <==> H3O+ (aq) + OH- (aq)
Hydroxium and hydroxide ion
Kw
Does changing the conc of [H+] or [OH-] cjnage Kw
No effect as equilibrium will shift to keep original value
Kw
Dies Kw change at different temps
Yes as dissociation of water is endo process
Kw
Dies the value change for pure water or aqueous
No is there same
Kw
What does p mean
-log
Kw
What does pKw mean
-log(Kw)
Kw
What is Kw useful for
Finding pH of strong bases
pH of strong bases
What will base produce in solution
OH- ions
pH of strong bases
What does a strong base mean
Will fully ionise in water
pH of strong bases
What it’s important for these calculations
Number of OH- ions per compound is dependant of number of OH
pH of strong bases What is [OH-] in 0.1 mol dm-3 of KOH
0.1 mol dm-3
pH of strong bases
What is [OH-] from 0.1 mol dm-3 Mg(OH)2
0.2 mol dm-3
pH of strong bases
How do you work out pH of a strong base of given conc
Find [OH-] from conc of base
Use rearranged Kw expression to find [H+]
Use pH=-log[H+]
pH of strong bases
What is also true for pOH and pH
pOH + pH =14 always in a base
Weak acids
What are weak acuds
Acids which do not fully dissociate in water
Weak acids
What does weak acids not fully ionising mean for the [H+]
Not the same as the acid concentration
Weak acids
What is Ka
Equilibrium constant with respect to acids
Weak acids
Acid dissociation equation for weak acid HA
HA <=> H+ + A-
Weak acids
What is an example of weak acid
Ethanoic CH3COOH
Weak acids
What is the Ka expression
Ka=[H+][A-]/[HA]
Weak acids
What is the units of Ka
Mol dm^-3
Weak acids
What is pKa
-log Ka
Weak acids
How do you find Ka from pKa
10^-pKa
Weak acids
What does the assumption that dissociation of acid is much greater then water mean you van asssume
All H+ ions in solution come from the acid so [H+]=[A-]
Weak acids
How else could you write Ka expression when only weak acid in aq and nothing else added
Ka=[H+]^2/[HA]
Weak acids
Since only small amount of HA dissociates what do we assume
[HA(start)]=[HA(equilibrium)]
Weak acids
How do you calculate pH of weak acid when given Ka and [HA]
Find [H+] using [H+]^2=Ka x [HA]
FindpH using -log[H+]
Weak acids
How do you find conc of weak acid given ph and Ka
Find [H+] from 10^-pH
Find conc using [HA]=[H+]^2/Ka
Reaction of weak acid and strong base
If 1 mol HA reacts with 1 mol OH- how much A- produced and how much OH- or HA left
1 mol A- produced
No OH- or HA left
Weak acids
If 3 mol HA and 1 mol OH- how much A- produced and OH- or HA left
1 mol A- produced
2 mol HA left
Weak acids and strong base reaction
If 3 mol HA and 10 mol OH- how much A- produced and OH- or HA left
3 A- produced
7 mole OH- left
Finding ph in reactions between weak acids and strong bases
What happens when a weak acid reacts with a strong base
For every one mole of OH- assed one mole of HA is used up and one mole of A- is formed
Finding ph in reactions between weak acids and strong bases
What is always the first three steps of these calculations
Calculate moles of HA
Calculate mole of OH-
Calculate moles of excess HA or OH-
Finding ph in reactions between weak acids and strong bases
What do you do if there is excess HA (acid)
- Calculate moles of HA left and A- formed
- Calculate HAconc left over and conc of A- formed
- Use Ka to find conc H+
7 find ph
Finding ph in reactions between weak acids and strong bases
What do you do if there is excess OH-
- Calculate conc OH-
- Use Kw to find conc H+
Find PH
Finding ph in reactions between weak acids and strong bases
What do you do if mole HA = OH-
Find ph using Ka of weak acid
PH curves and titrations
What can you use to measure the ph of a solution
A ph meter
PH curves and titrations
How do ph meters measure ph
Have a probe that is put into solution and a digital display which shows reading bulb at end of probe
PH curves and titrations
What do you have to do before using a probe meter
Calibrate it
PH curves and titrations
How do you calibrates a ph meter
Place bulb of ph meter into distilled water and allow the reading to settle now adjust the reading so that is reads 7.0
Then repeat with a standard solution of PH 4 and PH 10
PH curves and titrations
What should you do between every measurement using a ph probe
Rinse with distilled water
PH curves and titrations
What ph ph curves plot
Ph against volume of acid or base added
PH curves and titrations
What do titrations allow you to do
Find out exactly how much alkali or acid is needed to neutralise a quantity of acid or base
PH curves and titrations
What apparatus is used to generate ph curves
Ph meter and burette
PH curves and titrations
Why do ph curves vary in shape
Depending on the strength of acid and base used
PH curves and titrations
How do you find which acid or base is in the burette or conical flask
If ph above 7 at start, alkali is in the conical flask and can decide whether strong or weak from ph and the acid will be shown by u a low ph at the other side
Vice versa
PH curves and titrations
Why do ph curves have a flat start
Addition of small amount of acid or base has little impact on the ph of the solution
PH curves and titrations
What is the equivalence point on graph
Vertical section of the graph
PH curves and titrations
What is the equivalence point on graph
Vertical section of the graph
PH curves and titrations
What is the equals valence point
When [H+]=[OH-] neutralisation has occurred
PH curves and titrations
What is an end point in a titration
Point when indicator changes colour
PH curves and titrations
What does an indicator need to do
Change colour to show when sample has been neutralised
PH curves and titrations
When do you need your indicator to change colour
At the equivalence point of the titration
PH curves and titrations
How do you pick an indicator based on a PH curve
One which changes colour over a narrow ph range which lies entirely in the vertical part of the ph curve
PH curves and titrations
Which two indicators do we have to know about
Methyl orange and phenolpthalien
PH curves and titrations
What colour is methyl orange is a low ph
Red
PH curves and titrations
What colour is methyl orange in a high ph
Yellow
PH curves and titrations
What colour is phenolpthalien in low ph
Colourless
PH curves and titrations
What colour is phenolpthalien at a high ph
Pink
PH curves and titrations
What is the appoximate ph of colour change for methyl orange
3.1-4.4
PH curves and titrations
What is the approx ph of colour changed for phenolpthalien
8.3-10
PH curves and titrations
Which indicator should you use for a strong acid strong base titration and why
Either as there’s a rapid ph change over the range for both indicators
PH curves and titrations
Which indicators should you use for a strong acid weak base titration and why
Methyl orange as ph changes rapidly across the range for methyl orange but not for phenolpthalien
PH curves and titrations
Which indicator should you use for a weak acid strong base titration and why
Phenolpthalien as the ph changes rapidly across phenolpthalien range but not methyl orange
PH curves and titrations
What indicator should you use for a weak acid weak base titration and why
Neither as there’s not sharp ph change so neither of these indicators wold work
PH curves and titrations
What indicators would you use instead for a weak acid weak base titration
Ph meter
PH curves and titrations
What can indicators be thought of as and why
Weak acids as r they have differently colour conjugate pairs
PH curves and titrations
What happens as the colour changes
The equilibrium concentrations of the conjugate pairs also change this depend on whether the indicators is mainly protonated or deprotonated
PH curves and titrations
What is the ph of the end point equivalent to
The pKa value of HA
Buffers
What is a buffer
Solution that minimises changes in ph when small amounts of acid or base are added
Buffers
What volume do buffers work for
Only very small amounts of acid or base
Buffers
What are the two types of buffers and which ones do we need to know about
Acidic and basic
Only need to know acidic
Buffers
What do acidic buffers contain
A weak acid and a conjugate base
Buffers
What ph do buffers have
Less than 7
Buffers
How are acidic buffers a made
Setting up an equilibrium between a weak acid and its conjugate base
Buffers
What two ways can a buffer be made
Mix a weak acid with the salt of its conjugate base
Mix an excess of weak acid with a strong alkali
Buffers
How does the mixing a weal acid with the salt of its conjugate base work
Salt fully dissociates into its ions when it dissolves
Weak acid only slightly dissociates
Buffers
How does mixing an excess of weak acid with a strong alkali work
All the base reacts with the acid and as weak acid in excess there’s still some left in solution once all the base has reacted the acid slightly dissociates
Buffers
What is the mix of a buffer eg with Ethanoic acid
CH3COOH(aq) <==> H+(aq) + CH3COO-(aq)
Mix of both undissociate weak acid and conjugate base
Buffers
What does the equilibrium solution contain
Lots of undisscooated acid (HA)
Lots of the acuds conjugate bae (A-)
Enough H+ ions to make the solution acidic
Buffers
What is the job of the conjugate pair
To control the ph of the buffer to solution
Buffers
How does the conjugate base help control ph
Mops up excess of the H+ ions
Buffers
What does the conjugate acid do to help control the ph
Released H+ if too much base
Buffers
What happens to the equilibrium if you add a small amount of acid
H+ ion concentration increases and thr extra H+ ions co,bind with CH3COO- ions to form CH3COOH
Thus shifts the equilibrium to the left reducing H+ concentration to close to its original value
Buffers
How i there such large volumes of the conjugate base in the equilibrium
From weak acid only small proportions of H+ and A-
But on addition of A- , large proportions of A- and small volume of H+
Buffers
What happens if you have a small amount of alkali added
OH- conc increases which mostly react with H+ ions to form water removing H+ ions from the solutions, this causes the equilibrium to move to the right and H+ conc increases until it’s close to its original value
Buffers
What is used to find the ph of a buffer solution
Ka
Buffers
What is the equation to find the H+ ion conc
[H+] = (Ka[Acid])/[salt]
Buffers
Therefore what ratio does the ph of buffers depend on
Ratio of acid to salt
Buffers
Why cannot Ka just be simplified to [H+]^2
Have added excess OH-
Buffers
What two assumption have been made to calculate ph of buffer
[HA] remains constant was such small proportion dissociates
[A-] comes entirely from salt concentration