Chemistry 30
Equilibrium, Acids & Bases
A. Dynamic Equilibrium
30-D1.1k  define equilibrium and state the criteria that apply to a chemical system in
equilibrium; ie. closed system, constancy of properties, equal rates of forward and
reverse reactions
30-D1.1sts  explain that the goal of science is knowledge about the natural world

equilibrium theories and principles apply to a variety of phenomena in our world
eg)
blood gases in scuba diving
CO2 in carbonated beverages
buffers in our blood

reactions are often _______________________ which means that not only are the
_____________________________________________ but the
_________________________________________________

we use the double arrow to show this relationship
eg)

the forward and reverse reaction will proceed at different rates…it depends on the
concentration of the reactants and products
o if we start with only the reactants A and B, the _____________
___________________ will initially be the ________________ as it is the
__________________________________________
o as the products C and D are formed, the ___________________
_____________________________________________ and the
___________________________________________________
o at some point, the rates of forward and reverse reactions ______
________________________
Chemistry 30 EAB Notes
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
a system is said to be in a state of _______________________ when:
1. the _________ of the forward and reverse reactions are ___________
2. the ____________________________________________________ of the
system, such as temperature, pressure, concentration, pH are
_____________________
3. the system is a _______________ system at ____________________
__________________________________
B. Classes of Reaction Equilibria
30-D1.2k  identify, write and interpret chemical equations for systems at equilibrium

there are three classes of chemical equilibria:
1. ________________ favored (percent rxn __________)
2. _______________ favored (percent rxn ___________)
3. _______________ to the right (percent rxn _____________)
or
C. The Equilibrium Constant
30-D1.4k  define Kc to predict the extent of the reaction and write equilibrium law expressions
for given chemical equations, using lowest whole-number coefficients
30-D1.3s  write the equilibrium law expression for a given equation


experiments have shown that under a given set of conditions (P and T) a specific
quantitative relationship exists between the equilibrium concentrations of the
reactants and products
one reaction that has been studied intensively is that between H2(g) and I2(g)
(simple molecules and takes place in gas phase no solvent necessary!)
H2(g) + I2(g) ⇌ 2 HI(g)

when different combinations of H2(g), I2(g), and HI(g) were mixed and the
concentrations measured, it was discovered that ______________ was reached in
_______________________
Chemistry 30 EAB Notes
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
even though the equilibrium [ ] are_______________________, the
_____________________________________ was the same each time (within
experimental error)

this led to the empirical generalization known as the ______________
___________________________________________ which says that there is a
________________________________ between the concentrations of the
products and the concentrations of the reactants at equilibrium

this law can be expressed mathematically:
For the reaction
aA + bB ⇌ cC + dD
The law is:
where:
Kc = ______________________________________
A, B = __________________________
C, D = ________________________
a, b, c, d = _______________________ coefficients

________ is constant for a reaction at a given ___________________ …if you
change the temperature, Kc also changes


it is common to ignore the units for Kc and list it only as a numerical value (since
depends on the powers of the various [ ] terms)
when determining Kc use only the species that are in ____________ or
_______________________

the ________________ the value of Kc, the greater the tendency for the reaction
to favor the ____________________________________

if Kc is ________________________________, then the reaction is
_________________ favoured

if Kc is _________________________________, then the reaction is
_________________ favoured

Kc indicates the ____________________________________and not the
____________________________________________________
Chemistry 30 EAB Notes
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
catalysts will not affect the [ ] at equilibrium…__________________
________________________________________________________
Example 1
Write the equilibrium law for the reaction of nitrogen monoxide gas with oxygen to form
nitrogen dioxide gas.
2 NO(g) + O2(g) ⇌ 2 NO2(g)
Example 2
Write the equilibrium law for the following reaction:
CaCO3(s) ⇌ CaO(s) + CO2(g)
Example 3
Write the equilibrium law for the following reaction:
2 H2O(l) ⇌ 2 H2(g) + O2(g)
Example 4
Phosphorus pentachloride gas can be decomposed into phosphorus trichloride gas and
chlorine gas.
a) Write the equilibrium law for this reaction.
b) If the [PCl5(g)]eq = 4.3 x 10-4 mol/L, the [PCl3(g)]eq = 0.014 mol/L and the [Cl2(g)]eq =
0.014 mol/L then calculate Kc.
Chemistry 30 EAB Notes
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Example 5
Find the [SO3(g)] for the following reaction if Keq = 85.0 at 25.0C.
2 SO2(g)
+
0.500 mol/L
O2(g) ⇌
2 SO3(g)
0.500 mol/L
???
Your Assignment: pg 1 #1-4 “Chemical Equilibrium”
D. Graphical Analysis
30-D1.3s  interpret data from a graph to determine when equilibrium was established and to
determine the cause of a stress on the system

a graph of ___________________ vs. _____________ can be used to see when
equilibrium has been reached…as soon as the
concentrations_________________________________________, you can read
this time off the graph
Example 1
Consider this rxn:
Concentration
(mol/L)
2 SO2(g) + O2(g)  2 SO3(g)
SO3(g)
75
50
25
SO2(g)
O2(g)
0
10
20
30
Time (s)
At what time does equilibrium get reached and what is the value for Kc?
Your Assignment: pg 2 “Graphical Analysis”
Chemistry 30 EAB Notes
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E. Le Chatelier’s Principle
30-D1.3k  predict, qualitatively, using Le Chatelier’s principle, shifts in equilibrium caused by
changes in temperature, pressure, volume, concentration or the addition of a catalyst
and describe how these changes affect the equilibrium constant

_________________________________________________ states that when a
chemical system at ________________________ is disturbed by a
____________________________________________
_____________________, the system adjusts in a way ____________
__________________________________________

this takes place in a three-stage process
1. initial equilibrium state
2. shifting non-equilibrium state
3. new equilibrium state

a system can be affected by a change in concentration, temperature and or volume
(pressure)
1. Concentration Changes

an increase in the [ ] of the products or reactants favours
_______________________________________________

a decrease in the [ ] of the products or reactants favours
_______________________________________________
eg)
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
30-D1.3sts  explain that the goal of technology is to provide solutions to practical problems eg.
the Haber-Bosch process for producing ammonia

changes in concentration have _____________________ on the value of
____________
2. Temperature Changes

energy is treated like a ________________or __________________
eg)
reactants + energy ⇌ products
reactants ⇌ products + energy

if cooled, the equilibrium shifts so ____________________________
________________________________________________
Chemistry 30 EAB Notes
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
if heated, the equilibrium shifts _______________________________
________________________________________________

a change in temperature is the only stress that ___________________ the value of
Kc!!!!!!!

if the shift is towards the ____________ side, Kc will _____________

if the shift is towards the ____________ side, Kc will _____________
3. Volume (Pressure) Changes

with gases, volume and pressure are related
ie) volume ____, pressure ____

the concentration of a gas is related to volume (pressure)
ie) volume ____, concentration ______

the concentration of a gas is related to volume (pressure)

an _______________________________caused by a ____________ in volume
causes a shift towards the side of the equation with
______________________________
eg)
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
4 moles

2 moles
if the number of moles are the ________ on both sides of the reaction, a change in
volume (pressure) has _______________________

changes in volume and pressure have __________________ on the value of
__________
4. Colour Changes
 in many equilibrium systems, the reactants will have a different colour than the
products
 predictions can be made about the equilibrium shift and the resulting change in
colour
Chemistry 30 EAB Notes
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Example
Use the following reaction to predict the equilibrium shift and resulting colour change
when the stresses are applied
2 CrO42(aq) + 2 H3O+(aq) ⇌ 2 Cr2O72(aq) + 3 H2O()
yellow
orange
a) a crystal of Na2CrO4(s) is added
b) a crystal of K2Cr2O7(s) is added
c) a few drops of concentrated acid is added
d) water is removed
e) a few crystals of NaOH(s) are added
Your Assignment: pgs 3-4 “Le Chatelier’s Principle”
Chemistry 30 EAB Notes
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 all of the changes that can happen to systems in equilibrium can be shown
graphically:
30-D1.3s  interpret data from a graph to determine when equilibrium was established and to
determine the cause of a stress on the system
Example
State what change to the equilibrium takes place at each of the labelled parts of the graph:
Manipulations of An Equilibrium System
N2(g) + 3 H2(g) ⇌ 2 NH3(g) + energy
NH3(g)
N2(g)
Concentration
(mol/L)
H2(g)
A
B
C
Time (min)
Equilibrium
Stress
Time
A
B
C
D
Your Assignment: pg 5
Chemistry 30 EAB Notes
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D
F. ICE Tables
30-D2.3k  calculate equilibrium constants and concentrations for homogeneous systems and
Bronsted-Lowry acids and bases (excluding buffers) when
 concentrations at equilibrium are known
 initial concentrations and one equilibrium concentration are known
 the equilibrium constant and one equilibrium concentration are known
30-D2.3s  use experimental data to calculate equilibrium constants


we can use a table set-up to calculate the equilibrium concentrations and/or Kc for
any system
you must be able to calculate all ______________________________ before you
can use the equilibrium law
Example 1
Hydrogen iodide gas decomposes into hydrogen gas and iodine gas. If 2.00 mol of HI(g)
is place in a 1.00 L container and allowed to come to equilibrium at 35C, the final
concentration of H2(g) is 0.214 mol/L. Find the value for Kc.
Chemistry 30 EAB Notes
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Example 2
In a 500 mL stainless steel reaction vessel at 900C, carbon monoxide and water vapour
react to produce carbon dioxide and hydrogen. Evidence indicates that this reaction
establishes an equilibrium with only partial conversion of reactants to products. Initially,
2.00 mol of each reactant is placed in the vessel. Kc for this reaction is 4.20 at 900C.
Calculate the concentration of each substance at equilibrium.
Example 3
Gaseous phosphorus pentachloride decomposes into gaseous phosphorus trichloride and
chlorine gas at a temperature where Keq = 1.00  103. Suppose 2.00 mol of PCl5(g) in a
2.00 L vessel is allowed to come to equilibrium. Calculate the equilibrium [ ] of each
species.
Chemistry 30 EAB Notes
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
when the concentrations are greater than _______________________ the
equilibrium constant, we can make an ______________________ that greatly
simplifies our calculations

if Kc is very small, the equilibrium doesn’t lie very far to the right and
________________________________________________
***in this example, ___________ can be assumed to be ________ since x is really
_________, so…
Example 4
Gaseous NOCl decomposes to form gaseous NO and Cl2. At 35C the equilibrium
constant is 1.6  105. Calculate the equilibrium [ ] of each species when 1.0 mol of
NOCl is placed in a 2.0 L covered flask.
Your Assignment: pg 6 #1-5 “ICE Tables”
Chemistry 30 EAB Notes
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G. Ionization of Water

the equilibrium of water can be written as follows:

the equilibrium law is:
30-D2.2k  define Kw, Ka and Kb and use these to determine pH, pOH, [H3O+] and [OH] of
acidic and basic solutions

the equilibrium constant for water is designated as _______________

at 25C, neutral water has [H+(aq)] = [OH(aq)] = 1.0  107 mol/L
 Kw =
=

(on pg 3 of Data Booklet)
Kw is always constant and therefore can be used to determine the
_________________ or the ________________
eg)
if [H3O+(aq)] = 1.0  104 mol/L
then [OH(aq)] =
if [H3O+(aq)] = [OH(aq)], then solution is ________________
if [H3O+(aq)] > [OH(aq)], then solution is ________________
if [H3O+(aq)] < [OH(aq)], then solution is ________________
Try These:
1. [H3O+(aq)] = 1.0  109 mol/L
[OH(aq)] =
2. [H3O+(aq)] = 1.0  101 mol/L
[OH(aq)] =
3. [H3O+(aq)] =
[OH(aq)] = 1.0  102 mol/L
4. [H3O+(aq)] = 6.3  109 mol/L
[OH(aq)] =
5. [H3O+(aq)] = 8.1  103 mol/L
[OH(aq)] =
6. [H3O+(aq)] =
[OH(aq)] = 2.8  107 mol/L
Chemistry 30 EAB Notes
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H. Review of pH and pOH
30-D2.1k  recall the concepts of pH and hydronium ion concentration and pOH and hydroxide
ion concentration, in relation to acids and bases

the number of digits following the ____________________________ in the
______________________ is equal to the number of ______________________
in the ___________________
Example 1
Find the pH of a solution where the [H3O+(aq)] = 4.7  1011 mol/L.
Example 2
Find the pH of a solution where the [OH(aq)] = 2.4  103 mol/L.
Example 3
Calculate the [H3O+(aq)] if the pH of the solution is 5.25.
Chemistry 30 EAB Notes
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Example 4
Calculate the pH of a solution where 10.3 g of Ca(OH)2(s) is dissolved in 500 mL of
water.
Your Assignment: pgs 6-7 #1-11 “pH and pOH”
I. Brønsted-Lowry Definition of Acids & Bases (1923)
30-D1.3k  describe Bronsted-Lowry acids as proton donors and bases as proton acceptors

this theory looks at the role of the acid or base

an acid is a ______________________________________________
__________________________________________________________________
______________________________________________

a base is ________________________________________________

like in electrochemistry where e are transferred…now we transfer H+
H+
HCl(aq) + H2O(l) ⇌ H3O+(aq) + Cl(aq)
acid
H+
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH(aq)
base

water does not have to be involved!
H+
eg) HCl(g) + NH3(g) ⇌ NH4Cl(s)
Chemistry 30 EAB Notes
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
a Brønsted-Lowry acid doesn’t necessarily have to produce an acidic solution…it
depends on what accepts the proton

an acid/base reaction is a chemical reaction in which _____________ is
transferred from an _________ to a ___________ forming a
________________________ and a _______________________

this theory explains how some chemical species can be used to neutralize both
acids and bases
eg)
HCO3(aq) + H3O+(aq) ⇌
HCO3(aq) + OH(aq) ⇌

a substance that appears to act as a Brønsted-Lowry acid in some rxns and a
Brønsted-Lowry base in other rxns is said to be _____________
_______________________________________________________
eg)
Your Assignment: pgs 7-8 #1-2 “Brønsted-Lowry Acids and Bases”
J. Conjugate Acids and Bases
30-D1.7k  identify conjugate pairs and amphiprotic substances

a pair of substances that differ only by a proton is called a
___________________________________…the ___________ is on one side of
the rxn and the ___________ is on the other

in general, the reaction can be shown as follows:

HA(aq) + H2O(l) ⇌ H3O (aq) + A (aq)
+

the ____________ an acid, the _____________ its conjugate base

the ____________ an acid, the _____________ its conjugate base
Your Assignment: pg 8 #3
Chemistry 30 EAB Notes
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K. Strengths of Acids and Bases
30-D2.2k  define Kw, Ka and Kb and use these to determine pH, pOH, [H3O+] and [OH] of
acidic and basic solutions

two different acids (or bases) can have the same [ ] but have different strengths
eg) 1 M CH3COOH(aq) and 1 M HCl(aq) will react in the same way but not to the
same degree

the stronger the acid, the __________ electricity it conducts, the ___________ the
pH and the __________ it reacts with other substances
1. Strong Acids

acids that ionize _________________ in water to form H3O+(aq)

percent rxn = ______________

the bigger the Ka (Kc for acids) the more the ______________ are favoured

top 6 acids on the table (pg 11 in Data Book) have a very large Ka …note the
H3O+ is the strongest acid on the chart (leveling effect)…all strong acids react to
form H3O+(aq) so it is the strongest

when calculating pH, the __________________________________ so use
_________________________________________
Example
What is the pH of a 0.500 mol/L solution of HNO3(aq)?
2. Weak Acids

a weak acid is one that _____________________________________
_______________________________________________________

most ionize _________________

Ka value is __________________

to calculate pH, you need to use the ___________________…you cannot use just
the ___________ because it is not ________________
Chemistry 30 EAB Notes
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
the Ka law is an __________________________ is devised the same way we did
_________
eg) HA(aq) + H2O(l) ⇌ H3O+(aq) + A(aq)

you will be required to figure out the ____________ before you can calculate the
pH

you have the __________ and the __________ value but you don’t have the
_____________

since the mole ratio for __________________ is __________, they have the same
[ ] (this is a _________________!)

now you can solve for [H3O+(aq)]
Example 1
What is the pH of a 0.10 mol/L acetic acid?
Chemistry 30 EAB Notes
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Example 2
What is the pH of 1.0 mol/L acetic acid?
Example 3
A 0.25 mol/L solution of carbonic acid has a pH of 3.48. Calculate Ka.

the _____________________________________________ can be written as a
_______above the ______ in a chemical reaction:
1.3%
eg) CH3COOH(aq) + H2O(l) ⇌ H3O+(aq) + CH3COO(aq)
Ka = 1.8 x 105 mol/L
Chemistry 30 EAB Notes
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
the % reaction be calculated using [H3O+] and [HA]
Example 1
Calculate the % ionization for a 0.500 mol/L solution of hydrosulphuric acid if the
[H3O+(aq)] is 5.0  104 mol/L.
Example 2
The pH of a 0.10 mol/L solution of methanoic acid is 2.38. Calculate the % ionization.
Your Assignment: pg 8 #1-3 “Strengths of Acids”
3. Strong Bases

according to Arrhenius, bases are substances that increase the
___________________________ of a solution

all _________________________________ are strong bases
eg)

% reaction = _______________
Chemistry 30 EAB Notes
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
strength depends on ____________________________________
…_______________ is a stronger base than _______________ at the same [ ]
because it produces ________________

______________________________ where x is the number of ____________
ions (think about the dissociation equation!)

once you have the [OH(aq)], you can calculate the pH using pOH or KW
Example
Calculate the pH of a 0.0600 mol/L solution of Ca(OH)2(aq).
4. Weak Bases

do not ________________________________ in water…just like weak acids

Kb is the dissociation constant or equilibrium constant for bases
B(aq) + HOH(l) ⇌ BH+(aq) + OH(aq)

you can calculate Kb using _________ for the _____________

_________________________________________
eg) Calculate Kb for SO22(aq).
Chemistry 30 EAB Notes
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

once you have Kb, you can then solve for [OH(aq)] using the equilibrium law
(just like with weak acids!)
now you can solve for [OH(aq)]
Example
Find the pH of a 15.0 mol/L NH3(aq) solution.
Your Assignment: pg 9 #1-3 “Strengths of Bases”
pg 9 #1-10 “Strengths of Acids and Bases – pH Calc”
Chemistry 30 EAB Notes
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L. Predicting Acid-Base Equilibria
30-D1.6k  write Bronsted-Lowry equations, including indicators, and predict whether reactants
or products are favoured for acid-base equilibrium reactions for monoprotic and
polyprotic acids and bases

acids are listed in order of __________________ strength on the left side and
bases are listed in order of ________________ strength on the right side

when predicting reactions, the substance with ___________________
_____________________________ will react with the substance that
____________________________________________________

we will assume that only _________________ is transferred per reaction

to predict the acid-base reaction, follow the following steps:
Steps:
1. _______________________________________________________
Note:  ______________________________________________
 ______________________________________________
 ______________________________________________
 ______________________________________________
2. Identify all possible __________________________________.
3. Identify the ___________________ and _________________…like redox rxns
the ____________________________ and the
______________________________.
4. To write the reaction, ______________________________________
________________________________________________________
5. Predict the position of the equilibrium.
Note:  ________________________________________________
 ________________________________________________
Example 1
Predict the acid-base reaction that occurs when sodium hydroxide is mixed with vinegar.
Chemistry 30 EAB Notes
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Example 2
Predict the acid-base reaction when ammonia is mixed with HCl(aq).
Your Assignment: pg 10 #1-13 “Predicting Acid-Base Reactions”
M. Monoprotic vs. Polyprotic Acids and Bases

an acid capable of donating only one proton is called _____________
eg) __________________________________________

if an acid can transfer more than one proton, it is called ___________
(____________ if 2 protons, ___________ if 3 protons
eg) Label each of the following acids as monoprotic or polyprotic:
1. H2SO4(aq)
2. HOOCCOOH(aq)
3. HCOOH(aq)
4. CH3COOH(aq)
5. H2PO4(aq)
6. NH4+(aq)

a base that can accept only one proton is called _________________

a base that can accept more than one proton is called _____________
(_____________ or ____________)
eg) _____________ can accept up to 3 H+ to form__________,
________________, and _______________ respectively
eg) Label each of the following as monoprotic or polyprotic acids, bases or
polybasic:
1. HSO4(aq)
2. H2PO4(aq)
3. HPO42(aq)
4. HCO3(aq)
5. H2O(l)
Chemistry 30 EAB Notes
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
reactions involving polyprotic acids or polybasic substances involve the same
principles of reaction prediction

only _____________________ is transferred at a time and always from strongest
acid to strongest base
Example 1
Potassium hydroxide is continuously added to oxalic acid until no more reaction occurs.
Example 2
Sodium hydrogen phosphate is titrated with hydroiodic acid. If we assume all steps are
quantitative, show all steps and give the net reaction.
Your Assignment: pg 11 #1-5 “Polyprotic Acids and Bases”
O. Titrations
 titrations are used to determine the pH of the ___________________ of acid-base
reactions

the information from the titration can be plotted on a graph, buffer regions can be
analyzed and stoichiometric calculations can be performed
Chemistry 30 EAB Notes
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1. pH Curves
30-D1.3s  interpret, qualitatively, titration curves of monoprotic and polyprotic acids and bases
for strong acid-weak base and weak acid-strong base combinations, and identify
buffering regions

a ________________ is a graph showing the ____________________
________________________________________________________

graph of __________________ vs ____________________________

the _________________ is the point (usually shown by a change in indicator
colour) when the reaction has gone to completion

the ________________________ is the ______________ of titrant required for
the reaction to go to completion

they contain a relatively flat region called the ___________________

all pH curves have 4 major features:
o the _____________________________ of the curve must be the pH of the
_____________________
o the co-ordinate of the ________________________________ must be
correct in terms of _______ and __________________
o the ______________________________ must be
_____________________ (approaches but never touches) with the pH of
the __________________
o ___________________________________________________ must
match the ______________________________________
_________________________________________ occurring

titrant selection:
o if the sample is an acid, titrant should be a _________________ such as
_______________________________________
o if the sample is a base, titrant should be ___________________
___________________________________________________
Chemistry 30 EAB Notes
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
you need to be able to interpret pH curves:
1. Strong Monoprotic with Strong Monoprotic
o pH of __________ at the equivalence point
14
pH
14
7
pH
0
7
0
volume
volume
2. Weak Monoprotic with Strong Monoprotic
o if weak acid, then pH of _______ at equivalence point
o if weak base, then pH of _______ at equivalence point
o bottom “flat” region is _________________________
___________________________________________
14
pH
14
7
pH
0
7
0
volume
volume
3. Strong Polyprotic with Strong Monoprotic
o ___________________________________________
14
pH
14
7
0
pH
0
volume
Chemistry 30 EAB Notes
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27
volume
2. Indicators

an indicator is a substance that ____________________________ when it reacts
with an ______________________________ and are usually
____________________________ themselves

they exist in one of two conjugate forms that are reversible and distinctly different
in color

recall that to show the equivalence point of an acid-base titration, choose an
indicator:
1. whose ___________________________________________ includes the
______________________________________ of the titration
2. that will react _________________________________________ …this
means the indicator is a weaker acid or base than the sample
Your Assignment: pgs 11-12 #1-5 “pH Curves”
3. Buffers

________________ are chemicals that, when added to water, protect the solution
from __________________________________________
_______________________________________________________

they are used to __________________________ and _____________
_________________________________________________

typical buffers are solutions containing relatively large amounts of
__________________________________ such as a ______________ and the
____________________________________________ typical buffers are
eg) _______________________________

the ___________ in the conjugate pair of the buffer protects against any
_____________ added

the ____________ in the conjugate pair of the buffer protects against any
_____________ added

buffers can be ___________________ by the addition of __________
________________________________________________________
Chemistry 30 EAB Notes
28
Example 1
Using an acetic acid – sodium acetate buffer system, show what happens when:
a) a small amount of HCl(aq) is added
b) a small amount of NaOH(aq) is added
Your Assignment: pg 12 #1-2 “Buffers”
Chemistry 30 EAB Notes
29