Download CHEM121 Exam 4 ObjectivesW16

Chemistry 121
Exam 4 Objectives
Chapters 8, 9, & Chemical Reactions & Titration Labs
Chapter 8: Solutions
Solvent, solute, electrolyte, nonelectrolyte, saturated, dilute, concentrated , solubility rules
-calculate Molarity
-use Molarity to find # of moles or volume
Concentration-dependent Properties:
-vapor pressure lowering
-boiling point elevation
-freezing/melting point depression
-osmotic pressure
Titration Lab –find the molarity of an acid
Chapter 9: Chemical Reactions (Energy, Rate, Equilibrium)
Identify exothermic & endothermic reactions
Draw or interpret “energy diagrams” for exothermic & endothermic reactions
Know factors that affect reaction rate
Write equilibrium constant expressions
Calculate equilibrium constants (given concentrations of reactants/products)
Interpret equilibrium constants (large/small are products/reactants favored?)
LeChatelier’s Principle
-shift Left or Right in response to change in concentration, temperature, pressure
Classifying Chemical Reactions by pattern
Complete & Balance Single/Double Replacement Reactions & Combustion Reactions
Predict if a reaction takes place (use solubility rules and activity series)
Write Net Ionic Equation for precipitation or neutralization reactions
Identify products as (s), (l), (g), (aq)
Chapter 10 Acids & Bases
Define: Acid, Base, Strong acid/base, Weak acid/base
Write equation for dissociation of weak acid
Write Ka expression for weak acid
Define: pH = -log[H3O+]; pOH = -log[OH-]
Kw = [H3O+][OH-] = 1 x 10-14
pKw = pH + pOH = 14
Fill in Table of [H3O+], [OH-], pH, pOH, Acidic/Basic
Given Ka, find pKa
Identify the role of a buffer, find the pH of a buffer
Practice Questions for Exam 4
1. Write the Net Ionic Equation for the dissociation of silver nitrate in aqueous solution: AgNO3(s) 
2. Find the molar mass of Mg(HCO3)2.
3. 33.5 grams of CaCl2 are dissolved in water to give 500.0 mL of solution:
a) Identify the solute and the solvent; b) What is the Molarity
4. Compare the boiling point, freezing point and osmotic pressure of solutions that are 1.0M NaCl & 1.0M
glucose.
5. Compare what happens to cells placed in hypotonic vs. hypertonic solutions.
6.
25.0 mL of hydrochloric acid were titrated with 0.125M sodium hydroxide.
35.6 mL of the base were required to reach the equivalence point.
a. Write a balanced equation .
b. What was the Molarity of the acid?
7. Is the following reaction exothermic or endothermic?
PCl3(g) + Cl2(g)
PCl5(g) + heat
8. Label the following on an “energy diagram” for an endothermic reaction: energy of reactants,
energy of products, activation energy (Ea), change in heat energy (H).
9. Write equilibrium constant expressions:
Ag+(aq) + Cl-(aq)
AgCl(s)
PCl3(g) + Cl2(g)
PCl5(g) + heat
a. Calculate the value of the equilibrium constant if the equilibrium concentrations of the three
gases are: 3.5M PCl3
0.12M PCl5 8.4M Cl2
b. Predict which way the equilibrium will shift if the pressure is increased/decreased:
-if the temperature is increased/decreased
-if the concentration of PCl3 is increased/decreased
-if a catalyst is added.
10. Do the Reaction Prediction Worksheet
11. Write the Oxidation & Reduction half-reactions for the following Single Replacement reaction:
1.
FeCl2 + Zn
ZnCl2 + Fe
Find the pKa of the following weak acid (record the pKa to 2 decimal places):
Ka
Weak acid:
HA
2.
3.
4.
pKa
5.5 x 10
-6
Write an equation for the dissociation of a weak acid in water:
Identify the conjugate base of H2CO3.
A buffer solution is made with the following concentrations of acid and its conjugate base.
What is the pH of the buffer? (see question 1 for the Ka of the acid)
[HA] = 0.050M [A-] = 1.5M
5. Fill in the Table: (record pH/pOH to 1 decimal place)
[H3O+]
1 x 10-8
pH
[OH-]
pOH
1 x 10-4
2.0
7.0
6.5 x 10
-3
3.5
acidic/basic/neutral?
Practice Questions for Exam 4
1. AgNO3(s)  Ag+(aq) NO3-(aq)
2. Find the molar mass of Mg(HCO3)2.
146.35 g/mole
3. solute = calcium chloride, solvent = water; M = (33.5/110.98)/0.5000L = 0.605M
4.
electrolyte
B.P.
higher
m.p.
lower
osmotic P higher
nonelectrolyte
high
low
high
5. hypotonic swell; hypertonicshrink
a. HCl + NaOH  NaCl + H2O
6.
b. (0.125)(35.6)/25.0 = 0.178M
7. exothermic
8. (see figure)
9. Keq = [Ag+][Cl-];
a.
b.
11.
Keq = 0.12/(3.5 x 8.4) = 4.1 x 10-3
increased pressure will shift to the right
increased temperature will shift to the left
increased PCl3 will shift to the right, etc.
Zn2+ + 2e-
oxidation ½ reaction: Zn
reduction ½ reaction: Fe2+ + 2eFe
1.
Find the pKa of the following weak acid (record the pKa to 2 decimal places):
Ka
Weak acid:
HA
2.
5.5 x 10-6
pKa
5.26
HA + H2O  H3O+ + A-
3.
HCO3
4.
pH = 5.26 + log(1.5/0.050) = 6.74
5. Fill in the Table: (record pH/pOH to 1 decimal place)
[H3O+]
1 x 10-8
1 x 10-10
1 x 10-2
1 x 10-7
6.5 x 10-3
3.0 x 10-11
pH
8.0
10.0
2.0
7.0
2.2
10.5
[OH-]
1 x 10-6
1 x 10-4
1 x 10-12
1 x 10-7
1.5 x 10-12
3.3 x 10-4
pOH
6.0
4.0
12.0
7.0
11.8
3.5
acidic/basic/neutral?
B
B
A
N
A
B