Exam 3 Flashcards
(103 cards)
1
Q
Buffer solution
A
contains a weak acid and base conjugate pair
2
Q
What is pH based on?
A
the acid-conjugate base ratio
3
Q
What does pH equal?
A
-log [H+]
4
Q
Henderson Hasselbach Equation (given on the exam)
A
pH=pka+log(conjugate base/acid)
5
Q
Buffer capacity
A
amount of acid or base the buffer can neutralize without a significant pH change
6
Q
Buffer is no longer effective when outside the range..
A
0.1< (conjugate base)/(weak acid)<10
7
Q
Adding more acid (+H) does what?
A
makes it more acidic
8
Q
Adding more base (OH-) does what?
A
makes it more basic
9
Q
Adding a strong acid or strong base reacts (and removes) what? And what does this change?
A
Removes part of the buffer and changes the (base)/(acid) ratio
10
Q
Strong acid reacts with and removes what?
A
conjugate base and component buffer
11
Q
Strong base reacts with and removes what?
A
the weak acid component of the buffer
12
Q
Tirations
A
analytical technique using acid-base reaction and a solution with known concentration to determine something about the other solution
13
Q
What are the four regions of a titration curve?
A
- Initial pH
- Between initial and equivalence
- Equivalence point
- After Equivalence
14
Q
Details of the four regions for:
Titration Curve: Strong Acid-Strong Base
1. Inital pH
A
pure acid
15
Q
Details of the four regions for:
Titration Curve: Strong Acid-Strong Base
2. Between initial and equivalence
A
some base will neutralize the acid and some acid will remain
16
Q
Details of the four regions for:
Titration Curve: Strong Acid-Strong Base
3. Equivalence Point
A
- pH= 7,
- moles OH- added = moles H+ initial
17
Q
Details of the four regions for:
Titration Curve: Strong Acid-Strong Base
4. After Equivalence
A
- excess base
- pH =7
- Find the concentration of OH- bc dilution
18
Q
When does the Equivalence point occur?
A
when moles of base = moles of acid
19
Q
Details of the four regions for:
Titration Curve: Weak Acid-Strong Base
1. Initial pH
A
Normal weak acid
20
Q
Details of the four regions for:
Titration Curve: Weak Acid-Strong Base
2. Between initial and equivalence
A
- After has some weak acid and weak base
- Some weak acid reacts with all of added base
- Forms weak conjugate base
- Buffer Zone
21
Q
Details of the four regions for:
Titration Curve: Weak Acid-Strong Base
3. Equivalence Point
A
- All weak acid is converted to conjugate weak base
- pH > 7 due to conjugate weak base
22
Q
Details of the four regions for:
Titration Curve: Weak Acid-Strong Base
4. After Equivalence
A
- Excess OH-
23
Q
What does a titration indicator show?
A
endpoint (equivalence)
- need a color change at (or near)
equivalence
24
Q
What is this curve shape for?
And what is the pH?
A
Strong Acid- Strong Base
- pH= 7
25
What is this curve shape for? And what is the pH?
Weak Acid-Strong Base
- pH>7
26
What is this curve shape for? And what is the pH?
Strong base- Strong Acid
- pH=7
27
What is this curve shape for? And what is the pH?
Weak Base- Strong Acid
- pH<7
28
(question like this will be asked on the exam)
1. a= 8.2 b= 7.0
2. a= Weak Acid. b= Strong Acid
29
What is different about the titration of polyprotic acids?
there will be multiple equivalence points
30
For Titration of a Polyprotic Acid what will happen is Ka1>Ka2?
There will be two equivalence points in the titration
31
For the Titration of a Polyprotic Acid, the closer the Ka's are to each other, then what?
the less distinguishable the equivalence points are
32
1. When Dilute NaOH is added:
- It will react with the Weak
acid(CH3NH3)the concentration of
CH3NH3 goes down and the
concentration of CH3NH2 goes up.
-The reaction will shift right and the
pH goes up.
2. When Dilute HCl is added:
-It will react with the Weak
Base(CH3NH2)
-Concentration of CH3NH2 goes
down and the concentration of
CH3NH3 goes up
- The reaction will shift left and the
pH goes down
3. When solid CH3NH3 +Cl- is added:
- Product is added so the reaction
will shift left and the pH will go
down
33
Preparing a Buffer Summary
34
The first law of Thermodynamics
Energy can't be created or destroyed
- Total energy is constant
35
Reaction Enthalpy equation
delta H= products - reactants
36
Spontaneous process
a process that proceeds without outside interference
37
Reversible Process
May be restored original states by EXACTLY reversing the process
(ex: water freezing, melting, repeat)
38
Irreversible Process
Cannot be undone by exactly reversing the change to the system
(ex: dropping eggs bc you can't unbreak an egg)
39
Entropy
possibilities of how energy is dispersed
(related to the various modes of motion in molecules)
40
Formula for Entropy
delta S= S final- S initial
41
What does isothermal mean?
same temperature
42
Second Law of Thermodynamics
If a process occurs in a closed system, the entropy of the system increases for irreversible processes and remains constant for reversible processes
43
The energy of the universe is what?
is always increasing and never decreasing
44
delta S univ (entropy of the universe)=0
Reversible
45
delta S univ (entropy of the universe)>0
Irreversible
46
delta S univ (entropy of the universe)>(or equal to) 0
spontaneous
47
The more complicated a molecule is the what?
the more types of motion and higher entropy
48
Microstate
one particular set (arrangement) of positions and kinetic energies
49
Entropy is an absolute..?
quantity
50
Third Law of Thermodynamics
The entropy of a pure (perfect) crystalline substance at absolute zero is zero
51
The number of microstates and therefore entropy tends to increase with increases in what?
1. Temperature
2. Volume
3. The number of independently moving molecules
52
In general, when does entropy increase?
1. when gases form from solids and liquids
2. Liquids or solution are formed from solids
3. The number of gas molecules increases
4. The number of moles increases
53
What state will have the greatest entropy?
gases
54
S°
standard molar entropies
55
Formula for standard entropy change:
56
Formula for Gibbs Free Energy
57
ΔG<0
the reaction is spontaneous in the forward direction
58
ΔG=0
the reaction is at equilibrium
59
ΔG>0
the reaction is nonspontaneous in the forward direction
60
When ΔH is - and ΔS is + is the reaction spontaneous or nonspontaneous?
The reaction is spontaneous at all temperatures
61
When ΔH is + and ΔS is - is the reaction spontaneous or nonspontaneous?
The reaction is nonspontaneous at all temperatures
62
When is ΔH and ΔS temperature dependent?
When they are both either + or -
63
When ΔH and ΔS are both + is the reaction spontaneous or nonspontaneous?
In low temperatures, it is nonspontaneous and in high temperatures it is spontaneous
64
When ΔH and ΔS are both - is the reaction spontaneous or nonspontaneous?
In low temperatures, it is spontaneous and in high temperatures it is nonspontaneous
65
What is the formula for ΔG rxn at 25 degrees celsius?
ΔGrxn= ΔGproducts - ΔGreaction
66
What is the formula for ΔGrxn at temperatures other than 25 degrees?
ΔGrxn= ΔHrxn - TΔSrxn
67
under any conditions, standard or nonstandard, how can the free energy change be found (what equation)
ΔG=-RTlnK (given on exam)
68
What is step 1 of balancing redox reactions?
create half-reactions
69
What is step 2 of balancing redox reactions?
Make sure the half-reactions are balanced
70
What is step 3 of balancing redox reactions?
Balance O by adding H2O
71
What is step 4 of balancing redox reactions?
Balance H by adding H+
72
What is step 5 of balancing redox reactions?
Balance the electrons
73
What is step 6 of balancing redox reactions?
Multiply the half-reactions by integers so that the electrons gained and lost are the same
74
What is step 7 of balancing redox reactions?
Add the half-reactions, subtracting things that appear on both sides
75
What is step 8 of balancing redox reactions?
once the equation is balanced,
- add OH- to each side to "neutralize" the H+
- make H2O in place of H+ (you might have to subtract water from each side)
76
Voltaic Cell (aka galvanic cell)
a device that uses a redox reaction to generate electrical work and directs the path of electrons through an external pathway
77
Voltaic Cells in spontaneous (delta G<0) redox reactions
1. electrons are transferred
2. energy is released
3. work can be done (batteries!)
78
voltaic Cells separate an overall reaction into what?
A 1/2 reaction
79
On what side of Line notation is an anode?
on the left
80
On what side of the Line notation is a cathode?
on the right
81
What charge is the Anode?
negative
82
What charge is the cathode?
positive
83
Anode is what part of a redox reaction?
Oxidation (AN OX)
84
Cathode is what part of the redox reaction?
Reduction (RED CAT)
85
On the Anode side the electrode gets?
smaller
86
On the Cathode side, the electrode gets?
larger
87
Where do the Anions migrate towards?
the Anode
88
Where do the Cations migrate towards?
the cathode
89
What is the purpose of the salt bridge?
it balances the charges ( and it allows ion migration)
90
What is the purpose of the Voltmeter?
it directs electrons and harvests work
91
Definition of: Cell Potential
the potential energy difference between two electrodes
- Electromotive Force (denoted emf or
Ecell)
92
What is the value of the Ecell for spontaneous processes?
For spontaneous processes the Ecell is POSITIVE (Ecell>0)
93
E°
standard electrode potential symbol
94
E° for reductions in half-reactions under standard conditions:
1. Standard=1M concentrations and 1atm pressures
2. Typically at 25 degrees Celcius
95
What is the unit for E°?
Volt (V)
-1V=1 J/C
96
E°cell formula
E°cell= E°(cathode) - E°(anode)
97
If we want E° to be positive what will happen with the cathode?
the cathode will have
1. more positive E°red
2. For a spontaneous reaction use half-reaction as written
98
If we want E° to be negative what will happen with the anode?
1. more negative E°red
2. for a spontaneous reaction reverse half-reaction to be a oxidation half-reaction
99
Formula for Cell potential and free energy
ΔG= -nFE (given on exam)
100
For the formula for cell potential and free energy (ΔG= -nFE), if ΔG is negative and E is positive is the reaction spontaneous or nonspontaneous?
spontaneous
101
For the formula for cell potential and free energy (ΔG= -nFE), if ΔG is positive and E is negative is the reaction spontaneous or nonspontaneous?
nonspontaneous
102
For the formula for cell potential and free energy (ΔG= -nFE), if ΔG=0 and E=0 is the reaction spontaneous or nonspontaneous?
the reaction is at equilibrium
103
For the formula for cell potential and free energy,ΔG= -nFE, what do the letters stand for?
ΔG= Gibbs free energy
-n= moles of electrons
F= faraday's constant--> 96,485J/V
E= cell (or rxn) potential
