40S Chemistry Final Exam Problem Review Sheet

Mr. Storie 40S Chemistry Final Exam Review

40S CHEMISTRY FINAL EXAM PROBLEM REVIEW SHEET:

**THIS IS NOT A COMPLETE REVIEW. CONTINUE TO READ ALL COURSE NOTES, GO OVER ALL WORKSHEETS, HANDOUTS, AND THE MID-TERM EXAM TO BE BETTER PREPARED.

To prepare for this exam:

1. Make a schedule and stick to it.

2. Be sure you have a complete set of notes, and STUDY them.

3. Re-do old tests, quizzes and assignments.

4. Do it again, and again, and again.

5. Seek help if you are confused or need clarification. (I’ll be in room 118)

Unit # 1 - Atomic Structure

Ø Isotopes & Relative atomic mass

Ø Electromagnetic Radiation (wavelength, frequency, and energy)

Ø Energy level diagrams & Orbital diagrams

Ø Electronic configuration

Ø Periodic table trends

Ø Bonding

Ø Lewis Structures

Ø VSEPR Theory

Unit # 2 – Kinetics (Reaction Rates)

Ø Calculating Rates

Ø Factors affecting rate

Ø Ways to speed up a reaction

Ø Collision Theory

Ø Energy diagrams (reaction pathway)

Ø Rate Laws

Unit # 3 – Equilibrium

Ø Equilibrium Constants (expressions)

Ø Equilibrium constant calculations

Ø Significance of equilibrium constant value

Ø Le Chatelier’s Principle

Ø Heterogeneous and homogeneous equilibria

Ø Reaction Quotients

Unit # 4 – Acids & Bases

Ø Properties

Ø Strong vs. Weak

Ø pH & pOH

Ø Salts of Weak acids and bases

Ø Titrations

Ø Ionization constants and percent ionization (dissociation)

Ø Common ion effect

Unit # 5 – Reduction and Oxidation and Electrochemistry

Ø Oxidation Numbers

Ø Balancing using oxidation numbers

Ø Balancing using ion-electron method (in acid or base)

Ø Galvanic Cells

Ø Standard reduction potentials

Ø Electrolysis (reactions occurring at anode and cathode)

Ø Faraday’s laws

ATOMIC STRUCTURE

1. Give the electron configuration for a neutral atom of manganese, strontium, and iron.

2. Write the short hand notation for the electron configuration of phosphorus, tungsten, and gold.

3. What is the wavelength of light with a frequency of 5.6 x1020 Hz?

4. What is the frequency of light with energy 4.3x 10-15 J ?

5. What is the energy of blue light that has a wavelength of 650 nm?

6. Draw an orbital box diagram of chromium. Which electrons would it lose to form a 2+ ion?

7. Calculate the number of orbitals in the third energy level. Show your work.

8. What is the energy required to boost the electrons in a mole of hydrogen atoms from level n = 1 to n = 3?

a. How much energy is released once these excited electrons return to their ground state n = 1?

b. What is the frequency of this radiation?

c. What is the wavelength of this radiation?

9. Draw Lewis dot diagrams and use VSEPR to predict the shapes of the following molecules. Include valence electron count and account for all electrons.

a) AlCl3 b) PO4-3 c) PH3 d) SF6 e) OCl2

10. Identify which molecules in question 9 are polar.

11. What is the general trend observed for ionization energy? Explain this trend for ionization energies; include reasoning for the trend in a group and the trend in a period.

12. What are the trends observed for electronegativity, and ionization energy?

13. By considering the electron arrangement for the atoms oxygen and nitrogen, explain why the first ionization energy of oxygen is lower than that of nitrogen in spite of the fact that the trend predicts the opposite. (Hint: draw the orbital box diagram of each)

14. Draw Lewis dot diagrams for the following molecules. Show the valence electron count and account for all electrons.

H2S b. XeF4

15. Using Lewis dot diagrams and VSEPR theory predict the shapes of the following molecules. Show the valence electron count and account for all electrons. Indicate the number of bonding pairs and lone pairs of electrons. Draw the 3-D representation of the molecules.

16. Explain the difference between polar covalent bonds, non-polar covalent bonds, ionic bonds and coordinate covalent bonds.

KINETICS PROBLEMS

The reaction, A + 2B à Products, was found to have the rate law, Rate = k[A][B]2. While holding the concentration of A constant, the concentration of B was increased from x to 3x. Predict by what factor the rate of the reaction will increase.

2. For the hypothetical reaction A + B à Products, the following initial rates of reaction have been measured for the given reactant concentrations.

Experiment / [A] (M) / [B] (M) / Rate (mol/(L∙hr))
1 / 0.010 / 0.020 / 0.020
2 / 0.015 / 0.020 / 0.030
3 / 0.010 / 0.010 / 0.005

a. Calculate the order for reactant A.
b. Calculate the order for reactant B.

c. Calculate the overall order for the reaction.
d. Write the rate law expression.
e. Solve for the specific rate constant, k. 5000

For a reaction with the rate law - rate = k [A]n [B]m - Determine the factor by which the rate changes if both [A] and [B] are doubled given the following values of “n” and “m”. Show all your work.
a. n=0, m=2
b. n=2, m=2
c. n=1, m=3

4. For the chemical reaction H2O2 + 2H+ + 2I- à I2 + 2H2O

the rate law expression is Rate = k[H2O2][I-]. The following mechanism has been suggested.

H2O2 + I- à HOI + OH-

OH- + H+ à H2O

HOI + H+ + I- à I2 + H2O

a. Define the term “intermediate” and identify all intermediates included in this reaction.

b. Determine which of the steps is the RDS, and explain how the conclusion was reached.

Draw a Potential Energy Diagram for the following exothermic reaction:

2 SO2 (g) + O2 (g) ßà 2 SO3 (g) ΔH° = -198 kJ

Label your diagram with the following information:
a. reactants (write the actual reactants)
b. products (write the actual products)
c. activated complex
d. activation energy
e. ΔH° = -198 kJ

6. If ammonia gas, NH3, reacts at a rate of 0.090 mol/L×s according to the reaction

4 NH3 (g) + 5 O2 (g) ßà 4 NO (g) + 6 H2O (g)

a. at what rate does oxygen gas react under the same conditions? 0.11 mol/L×s

b. what is the rate of formation of water? 0.14 mol/L×s

c. What is the rate of production of nitrogen monoxide? 0.090 mol/L×s

7. The reaction A + B + C ßà E + F + G was studied at 0°C and the following data was collected:

Trial [A] [B] [C] Initial Rate

(mol/L) (mol/L) (mol/L) (mol/L•s)

1 1.0 2.0 2.0 1.66

2 2.0 2.0 2.0 3.33

3 1.0 4.0 2.0 1.66

4 1.0 2.0 4.0 6.65

5 1.5 5.0 ? 7.25

a. What is the rate law for this reaction?

b. What is the value of the rate constant 0.42

c. What is the rate if [A] = 1.5 mol/L, [B] = 2.5 mol/L, [C] = 0.25 mol/L? 0.039 mol/L×s

d. What is the [C] in trial 5? 3.4 mol/L

8. Write the rate laws for the following elementary reactions

a. N2 (g) + 3 H2 (g) ßà 2 NH3 (g)

b. N2 (g) + 2 O2 (g) ßà 2 NO2 (g)

c. H2 (g) + Cl2 (g) ßà 2 HCl (g)

Determine the value of k in 8(a), when [N2] = 0.50 mol/L and

[H2] = 1.5 mol/L and NH3 is produced at a rate of 2.5 mol/L×s. 1.5

EQUILIBRIUM PROBLEMS

At 773 K, the reaction 2 NO (g) + O2 (g) ßà 2 NO2 (g) produces the following concentrations:

[NO] = 3.49 X 10-4M; [O2] = 0.80M; [NO2] = 0.25M.

a. What is the equilibrium constant expression for this reaction?
b. What is the equilibrium constant for the reaction? 6.4 x 105

2. Phosphorous pentachloride decomposes to phosphorous trichloride according to this equation:
PCl5 (g) ßà PCl3 (g) + Cl2 (g) Keq = 1.00 x 10-3

At equilibrium, [PCl5] = 1.00M and [Cl2] = 3.16 x 10-2M.

a. Calculate the concentration of PCl3. 3.16 x 10-2 M
b. Chlorine gas, Cl2 (g) is toxic. If we could manipulate the pressure of the container for this

reaction, how can we minimize the formation of this gas? Explain using your knowledge of Le Chatelier’s principles.

Consider the reaction:

2 HBr (g) ßà H2 (g) + Br2 (g)

Initially, 0.25 mol of hydrogen and 0.25 mol of bromine are placed in 500 mL reaction vessel and heated. The Kc for the reaction is 0.020. Calculate the concentrations at equilibrium. 0.78 M, 0.11 M, 0.11 M

For the given reaction of methanol, the equilibrium concentrations were found to be [CO] = 0.170 M, [H2] = 0.322, [CH3OH] = 0.0406. Find the value of Kc. 0.434

CH3OH (g) ßà CO (g) + 2 H2 (g)

Hydrogen peroxide can be decomposed as follows:

H2O2 (l) ßà H2 (g) + O2 (g) (endothermic)

Equilibrium is established in a 10 L flask at room temperature. Predict the direction of the equilibrium shift.

a. hydrogen gas is added to the flask.

b. The temperature is raised to 500 ºC.

c. The entire mixture is compressed into a smaller volume.

ACIDS AND BASES PROBLEMS

You have water at 25o to which you add 0.050 M NaOH.

Complete the chart:

[H3O+] / [OH-]
Before adding NaOH
After adding NaOH

This time with a weak base. Let’s add 0.0050 M NH4OH. Kb =1.77x 10-5.

[H3O+] / [OH-]
Before adding NH4OH
After adding NH4OH

3. If an acid has a hydronium concentration of 0.000036 M, what is the pOH of the solution? 9.6

What is the hydroxide ion concentration of a solution with a pH of 4.9? 8.0 x 10-10 M

What is the % ionization of a 2.5 M solution of acetic acid (Ka = 1.76 x 10-5). 0.27 %

The pH of 0.50M HNO2 is 4.85. Find Ka. 3.9 x 10-10

What is the concentration of phosphoric acid if 15.0 ml of the solution is neutralized by 38.5 mL of a 0.15 M NaOH solution? 0.13 M

Suppose 3.5% of a weak solution of 0.020 M monoprotic acid is ionized. Calculate the Ka.

2.5 x 10-5

Complete and balanced the following reactions:

a. Sulphuric acid plus potassium hydroxide à

b. Phosphoric acid + Ca(OH)2 à

c. Nitric acid and magnesium hydroxide à

A solution was made by dissolving 28.5 g of KOH in 0.50 L of water. If 0.250 L of this solution was titrated with 0.136 L of H2SO4, what is the molarity of the acid? 0.938 M

ELECTROCHEMISTRY

1. Consider the particles: Na+, Mg, Cl-, F2, H2O

a) Which can be oxidized? ______

b) Which can be reduced? ______

c) Which is the best reducing agent? ______

2. For each of the following cells (which may or may not be written according to the standard line notation) indicate which half-cell is the anode and which is the cathode.

a) Zn│Zn2+║Cu2+│Cu Anode: ______Cathode: ______

b) Ag│Ag+║Ni2+│Ni Anode: ______Cathode: ______

c) Sn│Sn2+║Au3+│Au Anode: ______Cathode: ______

3. Sketch a galvanic cell between copper and barium. Show the direction of electron flow and ion migration, identify the anode and cathode, the species present in each half-cell, indicate the voltage on a voltmeter, and label the electrodes. Also show the half-reactions, overall cell reaction and the Emf calculation.

4. For each of the following cells write half-reactions, give the balanced net cell reaction, and calculate the Emf of the cell.

a) Al3+(aq) + Mg(s) → Al(s) + Mg2+(aq)

b) Cr(s)│Cr3+(aq) (1.0 mol/L)║Ag+(aq) (1.0 mol/L)│Ag(s)

5. Write out anode and cathode reactions for the electrolysis of the following.

a) CaCl2(l) b) CuI2(l)

6. How many coulombs of charge must pass through a cell in order to deposit 9.45 g of zinc from a solution of zinc nitrate?

7. What happens in an oxidation reaction in terms of electrons?

8. What happens in a reduction reaction in terms of electrons?

9. Assign oxidation numbers to each atom in the following compounds.

a) H3SO4 b. HNO3

10. Which reactant in the following reaction is oxidized and which is the oxidizing agent?

CO(g) + PbO(s) → CO2(g) + Pb(s)

11. Balance the following equation using the oxidation number method.

HBr + HBrO3 → Br2 + H2O

12. Balance the following equations in acid or base as indicated in brackets.

Cu + HNO3 → Cu2+ + NO2 + H2O (acid)
N2O4 + Br- → NO2- + BrO3- (base)

13. Examine the cell below and answer the questions that follow.

a) Cathode reaction: ______

b) Anode reaction: ______

c) Overall reaction: ______

d) What is the cell voltage? ______

e) Label anode and cathode.

f) Indicate the direction of travel of ions and electrons.

g) While the cell operates which electrode gains in mass? ______

h) While the cell operates which electrode decreases in mass? ______