Download Untitled

Unit
5
1
This Unit covers Chapters 12, 13, and 15 (sections 1-3)
Suggested practice problems:
Chapter 12:
1-12, 15-20, 27-32, 43-46, 49-68
Chapter 13:
1-18, 31-50, 69-74, 77-78, 81, 83-86, 88, 91-94, 99-102
Chapter 15:
3-10, 13-22, 29-34, 39-46, 48-50, 53-68, 70, 75-78
Rates of Reactions
Demo:
Use models to represent the following reaction:
2H2 + O2 → 2H2O
For the reaction to occur, bonds must first be _____________, and then the new
____________ are formed.
Breaking bonds:
Forming bonds:
Endothermic and Exothermic Reactions
↑
E
↑
E
Ea: Activation Energy-the amount of ____________ needed to ___________
the necessary bonds
The energy to break bonds comes from:
Not all collisions cause a reaction, those that do are called:
2
Effective Collisions
To be effective the collision between molecules has to have
1.
2.
The higher the Ea the slower the reaction rate. Why?
Factors that affect the rate of a reaction
1.
Nature of reactants
Demo:
Compare the rates of the following reactions
a. 5H2O2 + 2 KMnO4 + 3H2SO4 → 5O2 + 2MnSO4 + K2SO4 + 8H2O
b. 5H2C2O4 + 2 KMnO4 + 3H2SO4 → 10CO2 + 2MnSO4 + K2SO4 + 8H2O
Which reaction has a faster rate?
Which has a higher Ea?
3
2. Size and Physical States of Reactants
Demo:
Drop whole and crushed Alka-Seltzer tablets into beakers of water.
Which tablet reacted fastest?
Why?
3. Concentration of Reactants
Demo:
Compare the rates of the following reaction when 1 M HCl and 6 M HCl are
used.
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Which concentration reacted fastest?
Why?
4. Temperature
Demo:
Drop whole Alka-Seltzer tablets into hot and cold water
Which temperature reacted fastest?
Why?
5. Catalyst A chemical that changes the rate of a reaction without being used up
Demo:
Add MnSO4 to reaction b above.
What happed to the rate?
How does a catalyst work?
4
Equilibrium
2 green '
The Bead Game
red + blue
Instructions:
Place 50 green beads in the plastic box. Simulate a collision by choosing two beads. Then
apply the following rules:
a. If both beads are green, remove them and replace with one red and one blue
b. If one is red and the other blue, remove them and replace with 2 green
c. If the beads are any other combination, don’t do anything.
Number of Collisions
Number of Green
Number of Red
0
25
50
75
As the game continues what happens to the possibility that 2 green will react?
How about a red and blue?
Use the computer to play for a long time.
Even after _______ turns are all the green gone?
Instead of all the green being converted to red and blue a “stale-mate” condition called
__________________ is produced, where both reactants and products are present.
Important Properties of a reaction at equilibrium
1. The reaction __________ stop.
2. The amounts of product and reactant are ___________.
3. If the reaction does not stop, how can the amount of product and reactant remain
constant?
So, what is “equal” at equilibrium?
5
Reversible Reactions
Type of arrow:
Example:
2NOBr(g) ' 2NO(g) + Br2(g)
What if we want to know how much bromine is produced once we reach equilibrium. Can we
use the mole map?
Why?
Equilibrium Constants (K)
aA + bB ' cC + dD Where the lowercase letters are the __________
K=
[]=
Note: We always put the __________ on the top and the ___________ on the bottom
When we calculate equilibrium constants we have to look at the state the reactants and
products are in. We only use ______ and ________ in the equilibrium constant expression.
So what do we do if we have a solid or liquid?
What units does K have?
Example 1:
Write the expression for the equilibrium constant for the reaction above
Example 2:
If the concentrations are as follows, calculate K
[NOBr] = 0.015
[NO] = 0.23
[Br2] = 0.046
Example 3:
Using the K calculated in example 2, calculate the [NO] if the other
concentrations are as follows.
[NOBr] = 0.27
[Br2] = 0.016
6
Practice Problems
H2(g) + CO2(g) ' H2O(g) + CO(g)
1.
Write the expression for the equilibrium constant and calculate it’s value if the
concentrations are as follows
[H2] = 1.83
[H2O] = 7.17
[CO2] = 7.31
[CO] = 2.04
2. Using the K found above determine the [CO] if the concentrations of the other gasses
are as follows
[H2] = 2.78
[H2O] = 5.74
[CO2] = 4.94
2NOCl(g) ' 2NO(g) + Cl2(g)
3. Write the expression for the equilibrium constant and calculate it’s value if the
concentrations are as follows
[NOCl] = 7.14
[NO] = 1.81
[Cl2] = 2.47
4. Using the K found above, determine the [NOCl] if the concentrations of the other gasses
are as follows
[NO] = 4.87
[Cl2] = 7.01
7
CO(g) + 2H2(g) ' CH3OH(l)
5. Write the expression for the equilibrium constant and calculate it’s value if the
concentrations are as follows
[CO] = 3.56
[H2] = 1.95
Answers
1. 1.09
2. 2.61
3. 0.159
4. 32.3
5. 0.0739
6. 1.24
6. Using the K found above, determine the [H2] if the concentrations of the other gas is as
follows
[CO] = 8.74
What does K tell us?
Large K (K > 1)
Small K (K < 1)
More_________, less ___________ at equilibrium
More_________, less ___________ at equilibrium
What relationship does K have with the rate of a reaction?
Le Chatelier’s Principle
At equilibrium the rates of the forward and reverse reactions are equal, so the concentration
of the reactants and products_______________________.
But what happens if we do something?
8
Demo: Make a solution of chromate and dichromate ions.
2CrO42- + 2H3O+ ' Cr2O72- + 3H2O
Color:
_________
__________
Add some H3O+, what color does the solution turn?
Add some base (which removes the H3O+), what color does the solution turn?
Remember the bead game; imagine the box at equilibrium with 2000 green, 1500 red, and 1500
blue. If we added 2000 more green beads what would happen to the chance that you would
pick 2 green beads?
What would happen to the chance that you would pick a red and blue?
Are the rates of the forward and reverse reaction still equal?
What will happen as the game is played?
Let the computer play the game
Color
Number at 1st
equilibrium state
Number
Added
Green
2000
2000
Red
1500
0
Blue
1500
0
Does the game come to equilibrium again?
Number at 2nd equilibrium
state
How?
How is this equilibrium state different from the first?
Le Chatelier’s Principle: When stress is applied to a system at equilibrium the system
__________ to relieve some of the stress.
Le Chatelier’s Principle is like:
9
Other factors beside adding or removing reactants or products can shift the reaction.
Temperature
Exothermic reaction- ________ heat
A'B
Endothermic reaction- __________ heat
A'B
Pressure (Volume)
2NOBr(g) ' 2NO(g) + Br2(g)
If the pressure is increased by decreasing the volume the reaction will shift toward the side
with the ________ number of moles of ______
What if the NO was a liquid and the pressure was increased?
10
Practice Problems
2NO(g) + O2(g) ' 2NO2(g) + heat
Which direction (toward reactants, toward products, neither direction) will the equilibrium shift
when
1.
The temperature is raised
2. O2 is added
3. The pressure is increased
4. NO2 is removed
5. The temperature is lowered
6. NO is added
7. NO2 is added
8. The pressure is decreased
9. O2 is removed
10. NO is removed
A catalyst is added
Answers
1. Reactants
2. Products
3. Products
4. Products
5. Products
6. Products
7. Reactants
8. Reactants
9. Reactants
10. Reactants
11. Neither
11.
11
Acids and Bases
Naming Acids
There are two types of acids
1. Binary Hydrogen bonded to a Group VIA element other than ______ or to a Group
VIIA element
2. Oxoacids (Ternary) Consist of three elements, hydrogen, oxygen, and (usually) a
_____________
Rules
acid
ending of anion
prefix
ending
binary
-ide
hydro
-ic
oxo
-ate
-ic
oxo
-ite
-ous
Name the following acids
HF
HCl
H3PO4
H2CO3
HClO4
HClO3
HClO2
HClO
HC2H3O2
HCN
H2SO3
H2SO4
Naming Bases
Most common bases are ionic compounds, and are named as such.
Examples:
NaOH
CaCO3
Al(OH)3
Properties of Acids
• ________ taste
Vinegar (acetic acid)
Lemon (citric acid)
•
Change colors of many indicators
Litmus
Phenolphthalein
12
•
Aqueous solutions of acids are electrolytes
Strong acids are ________ electrolytes
Weak acids are ______ electrolytes
Properties of Bases
• ______ taste
•
Slippery feeling
Soap (weak base)
Bleach (strong base)
•
Change colors of many indicators
Litmus
Phenolphthalein
•
Aqueous solutions conduct electricity
Usually __________ electrolytes
There are 3 main definitions of acids and bases; Arrhenius, Brønsted-Lowry, and Lewis. We
are going to learn about the ______________ and _________________ definitions.
Arrhenius Theory
Acid- Substance that contains _______ and produces ______ ions in aqueous solution
Example:
HCl(aq) →
H+(aq) + Cl-(aq)
Base- Substance that contains the OH (hydroxyl) group and produces _____ ions in aqueous
solution
Example:
NaOH(s) → Na+(aq) + OH-(aq)
Hydronium Ion
Arrhenius described H+ ions in water as bare ions, but we now know that they are hydrated
(attached to _______) in aqueous solution
H+(aq) + H2O(l) J H3O+(aq)
The “more correct” Arrhenius definition of an acid:
Substance that contains hydrogen and produces hydronium, H3O+, in aqueous solution
13
Brønsted –Lowry Theory
(The one we use most of the time)
The Arrhenius theory only works when we are in __________ solution so Brønsted and
Lowry independently expanded the Arrhenius theory
Acid-A proton ________
Base-A proton ________
Proton:
An acid-base reaction is the _____________ of a proton (H+) from an acid to a base
When an acid gives up a proton it becomes a base-called a _____________ ________
Example:
What is the conjugate base of HCl?
What is the conjugate base of H2SO4?
When a base gains a proton it becomes an acid-called a _____________ ________
Example:
What is the conjugate acid of NH2What is the conjugate acid of CO32-?
Conjugate acids and bases
In reactions we can identify the acid, base, and the conjugate acid and base.
HF(aq) + H2O(l) ' H3O+(aq) + F-(aq)
Acid:
Conjugate Acid:
Base:
Conjugate Base:
14
Practice Problems
1.
Give the conjugate acid for each of the following Brønsted-Lowry bases
a. NH3
b.
PO43-
c. ClO3d.
HCO3-
2. Give the conjugate base for each of the following Brønsted-Lowry acids
a. H2S
b.
HCO3-
c. HNO3
d.
NH4+
3. Identify the acid, base, conjugate acid, and conjugate base for each of the following
reactions.
a. NH2-(aq) + H2O(l) → NH3(aq) + OH-(aq)
b.
H2O(l) + H2C2O4(aq) → HC2O4- + H3O+(aq)
c. H3O+(aq) + HPO42-(aq) → H2PO4-(aq) + H2O(l)
d.
HC2O4-(aq) + CO32-(aq) ' C2O42-(aq) + HCO3-(aq)
e. H2O(l) + PH4+(aq)
' PH3(aq) + H3O+(aq)
15
CN-(aq)
+ NH4+(aq) ' HCN(aq) + NH3(aq)
Answers
1.
a. NH4+
b. HPO42c. HClO3
d. H2CO3
2.
a. HSb. CO32c. NO3d. NH3
f.
Acid Strength
Strong acids ionize completely (they are _________ electrolytes) in aqueous solution
Weak acids only partially ionize (they are ________ electrolytes) in aqueous solution
Strong acids produce ________ conjugate bases. Strong bases produce ________
conjugate acids. Why?
16
Ka
Remember that strong acids react _____________, but weak acids only ___________
react. So if we place a weak acid in water we will have a ________________ reaction
and eventually a system at ________________.
Example:
HA(aq) + H2O(l) ' H3O+(aq) + A-(aq)
Where HA is any ______ and A- is its ____________ _____
The equilibrium constant for this reaction is: K = Ka =
Ka is defined as the acid dissociation constant, and is the equilibrium constant for a weak acid
in water. Why don’t we use a Ka for strong acids?
What is the relationship between Ka and acid strength?
Example:
Write the expression for Ka for the following weak acids:
1. H2C2O4(aq)
2. HCO3-(aq)
3. NH3(aq)
4. H2PO4-(aq)
17
Reactions between acids and bases
HCl(aq)
Strong Acid
+
+
NaOH(aq)
→
Strong Base →
H2O(l) +
NaCl(aq)
Water
+
A Salt
This is called a ____________________ reaction.
A common use of neutralization reactions is ________________. Excess HCl in your
stomach causes heartburn and antacids are ________ that react with the HCl to neutralize
the acid and relieve the heartburn.
Example:
Look at the active ingredients of some antacids
Antacids
Active Ingredients
Antacids
Rolaids
Alka-Seltzer
Maalox
Milk of Magnesia
Tums
Mylanta
Active Ingredients
Self Ionization of Water
H2O(l) + H2O(l) ' H3O+(aq) + OH-(aq)
This reaction occurs _____________________ (in very small amounts) in water
In this reaction one water acts as an acid and the other acts as a base. Water is amphiprotic
Substances that are amphiprotic can act as ___________ an acid or a base.
K = Kw =
= 1 x 10-14
(exact number)
Kw is called the ion-product of water
Example:
What is the [OH-] if the [H3O+] = 4.82 x 10-5?
18
pH and pOH
The [H3O+] of any aqueous solution is a very important characteristic, and we often need to
talk about it. It is inconvenient to talk about the concentration in units such as 4.50 x 10-12 M
or numbers similar to this form. So scientist defined a new number called _____ to talk
about the concentration in a more convenient form. The formula for pH is:
pH =
Example 1:
What is the pH of a solution if the [H3O+] = 1 x 10-8?
Example 2:
What is the pH of a solution if the [H3O+] = 3.65 x 10-12?
Remember that the “antilog” is 10x. So, if we know pH we can calculate the [H3O+] using the
formula [H3O+] = 10-pH
Example 3:
What is the [H3O+] if the pH = 3.5?
Example 4:
What is the [H3O+] if the pH is 10.6?
We can also use pOH to talk about the [OH-]: pOH =
We can use the properties of logs and the Kw to get the formula:
and
[OH-] = 10-pOH
pH + pOH = 14
19
Acidic and Basic Solutions
14
0
__________solution
[H3O+]
pH 7
7
pOH
[OH-]
__________solution
[H3O+]
[OH-]
__________solution
0
[H3O+]
14
[OH-]
Demo: Use a pH meter to measure the pH of some household chemicals. Then calculate the
pOH and [H3O+] and [OH-]
Substance
Coke
7-UP
Drano
Lime-A-Way
Aspirin
Ammonia
Baking Soda
Mylanta
Toilet Cleaner
Clorox
Tide
pH
pOH
Acid or Base
[H3O+]
[OH]
20
Buffers
Example:
Add HCl and NaOH to water and phosphate buffer and record what happens to
the pH.
Solution
pH
pH with Acid added
pH with Base added
Pure Water
Phosphate Buffer
Buffer
a solution whose pH doesn’t ___________ very much when ________ or
______ ions are added.
How are they made?
How do they work?
21
Buffer Capacity-you _____________overload a buffer
Blood Buffers
pH of blood:
Change > ______ Pathological
pH <______ or > ______ you die
Made from:
Practice Problems
1.
Calculate the [OH-] if the [H3O+] is
a. 6.29 x 10-4
b.
8.20 x 10-7
2. Calculate the pOH of a solution if the [OH-] is:
a. 7.15 x 10-5
b.
5.61
4. Calculate the pH of a solution if the [OH-] is:
a. 8.14 x 10-5
b.
c. 4.27 x 10-12
2.78 x 10-2
3. Calculate the [OH-] if the pOH is:
a. 1.75
b.
c. 7.18 x 10-2
1.78 x 10-10
c. 6.90
d.
9.45
c. 3.47 x 10-1
Answers
1.
a. 1.59 x 10-11
b. 1.22 x 10-8
c. 1.39 x 10-13
2.
a. 4.15
b. 1.56
c. 11.4
3.
a. 0.0178
b. 2.45 x 10-6
c. 1.26 x 10-7
d. 3.55 x 10-10
4.
a. 9.91
b. 4.25
c. 13.5
5.
a. 7.72
b. 6.28
c. 5.29 x 10-7
6.
a. 3.15
b. 10.85
c. 1.40 x 10-11
7.
a. 8.19
b. 1.55 x 10-6
c. 6.46 x 10-9
8.
a. 12.18
b. 6.61 x 10-13
c. 0.0151
22
5. If the [OH-] = 1.89 x 10-8 calculate the
a. pOH
b.
6. If the [H3O+] = 7.13 x 10-4 calculate the
a. pH
b.
7. If the pH = 5.81 calculate the
a. pOH
b.
8. If the pOH = 1.82 calculate the
a. pH
b.
c. [H3O+]
pH
c. [OH-]
pOH
c. [OH-]
[H3O+]
c.
[OH-]
[H3O+]
23
Nuclear Chemistry
The chemistry we have talked about so far has dealt with what happens _________
the nucleus. Remember that there are 3 particles that make up an atom. The
_________ and ___________ reside inside the nucleus while the _________
(which are responsible for ions, bonding, reactions, electricity, light, and magnetism)
reside outside the nucleus. Nuclear chemistry deals with what happens _________
the nucleus.
Nuclear chemistry was “discovered” in the late ________ century and was studied
by Becqueril, Pierre and Marie Curie, and Rutherford.
Remember that each element has a number of __________. Some isotopes are
stable and some are not, those isotopes that are unstable will emit radiation to become
stable. These isotopes are called ______________
Types of Radiation
Alpha:
4
2He
238
92U
→
234
90Th
+
4
2He
210
84Po
→
+
4
2He
For a nuclear reaction to be balanced the ________ of the mass and atomic numbers
must be __________ on the reactant and product side
Beta:
0
-1e
Gamma: γ
Positron:
0
+1e
3
1H
→
3
2He
+
40
19K
→
40
19K
28
→
28
15P
14Si
0
-1e
131
+ γ
99
+
0
+1e
53I
42
43Tc
21Sc
→
→
→
0
-1e
+
+ γ
+
0
+1e
All radiation occurs at a ____________, set rate. We _____________ speed
up or slow down radioactive decay.
Our way of measuring the rate of radioactive decay is the __________. Half-life
is defined as the time it takes for ½ of any sample of radioactive material to decay.
The half-life for different chemicals can range from ______seconds to
___________ of years!
24
Iodine-131 has a half-life of 8 days. The decay curve is below:
25
Uses of radiation
Dating:
Since all radioactive decay occurs at a constant, set rate and we can not speed it up
or slow it down, we can use nuclear chemistry to “date” how old something is.
Organic Material
Carbon-14
14
6C
→
14
7N
+
0
-1e
T½ = _________
Assumptions.
1. The rate has always been the same.
2. The amount of 14C is the same now as it has always been.
Carbon-14 dating works well for about __________ years, after that it can be
suspect.
Inorganic Material
Age of the earth:
Determined using 40K →
40
Ar +
0
+1e
T½ = _______________
Medical uses
X-Rays
Images hard tissues (bones)
CT scan
Uses x-rays and the density of tissues-used to detect brain
tumors
MRI
Uses the “spin” of H atoms-useful to “see” the inside of the
body
Ultrasound
Images soft tissues with high water content.
PET scan
Uses positron emission of 11C-useful in detecting what parts of
the brain are working
Therapy
Ionizing radiation damages cells, especially those that divide
rapidly (cancer)
26
Energy
Fusion
2
1H
+
3
1H
→
4
2He
+
1
0n
+ energy
This is how the ______ makes its energy, hydrogen bombs work, and how scientists
make ______ elements
Fission
235
92U
+
1
0n
→
141
56Ba
+
92
36Kr
+ 3 10n + γ
Fission was discovered in the 1930s and is used in nuclear _______________ and
the _______________.
27
Notice-the reaction uses 1 neutron but produces ___ neutrons-thus the reaction is
self-propagating and often called a __________________
Nuclear Power plant:
28
Practice Problems
Fill in the blank for the following reactions
1.
184
0
+1e
2.
125
3.
____ →
4.
23
5.
59
6.
96
7.
238
8.
147
9.
_____ + 1H →
10.
40
11.
What would be the product if a
205
12.
What would be the product if a
116
Ir →
+ _____
0
-1e
Sn →
0
-1e
+ _____
40
+
Ca
23
Na + _____ →
1
Co +
→
4
2He
Mo +
1
0n
56
Mn + _____
→
100
Tc + _____
16
Sm →
O → _____ + 5 10n
____ +
29
143
Nd
Si + γ
Ar + _____ →
43
K + 1H
Po isotope underwent alpha emission?
In isotope underwent beta emission?
Answers
1. 184 76Os
2. 12551Sb
3. 4019K
4. 11H
5. 42He
6. 0+1e
7. 249100Fm
8. 42He
9. 2813Al
10. 42He
11. 20182Pb
12. 11650Sn
U +
0n
Mg +
Unit 4 Practice Test
You will be given any formulas needed on the test.
Use the following reaction for questions 1-4
N2(g) + 3H2(g) ' 2NH3(g) + Heat
1.
If the [N2] = 0.24, [H2] = 0.41, and the
[NH3] = 0.31 calculate the value of K
a. 3.2
b. 5.8
c. 0.17
d. None of the above
2. If the pressure is increased the equilibrium
will
a. Shift toward products
b. Shift toward reactants
c. Not shift at all
3. If H2 is added the equilibrium will
a. Shift toward products
b. Shift toward reactants
c. Not shift at all
4. If the temperature is increased the
equilibrium will
a. Shift toward products
b. Shift toward reactants
c. Not shift at all
5. What is the name of H2CO3
a. Carbonic acid
b. Hydrocarbonic acid
c. Carbonous acid
d. None of the above
6. An Arrhenius Acid is a chemical that
a. Produces OH- in water
b. Produces H3O+ in water
c. Donates a proton
d. Accepts a proton
Use the following reaction for questions 7-8
H3O+(aq) + HPO42-(aq) → H2PO4-(aq) + H2O(l)
7. Which chemical is the conjugate acid?
a. H3O+
b. HPO42c. H2PO4d. H2O
8. Which chemical is the base
a. H3O+
b. HPO42c. H2PO4d. H2O
9. If the pOH of a solution is 6.9 than the
[H3O+] is
a. 1.3 x 10-7
b. 5.9 x 10-5
c. 7.9 x 10-8
d. None of the above
10. If the pH of a solution is 4.2 then the pOH
is
a. 4.2
b. 18.2
c. 9.8
d. None of the above
11.
If the [OH-] = 1.87 x 10-4 than the solution
is
a. Acidic
b. Basic
c. Neutral
d. Can’t be determined without further
information
12.
209
14. The reaction in question 13 is a/an
________ reaction
a. Alpha emission
b. Beta emission
c. Fusion
d. Fission
Answers:
1.
B
2. A
3. A
4. B
5. A
6. B
7. C
8. B
9. C
10. C
11.
B
12. B
13. B
14. D
Po is an unstable isotope that decays by
emitting alpha radiation. What new isotope
would be formed?
a. 209At
b. 205Pb
c. 209Bi
d. 209Po
13. Fill in the blank for the following reaction
1
235
U → 137Te + _______ + 2 10n
0n +
a. 98Zr
b. 97Zr
c. 97Bk
d. None of the above