Dec. 1999 Professor Susan White

IMPORTANT NOTE--For partial credit be sure to show your reasoning. Please attempt all parts of all problems--no partial credit can be given for blank spaces. If you need more paper, write on the back of the page and indicate clearly that you have done so. You may use a calculator. This examination is closed book. There are 11 numbered pages and 1 additional pages of supplementary information. Please Hand in your HW notebooks.

NA = 6.022 x 1023 R = 3.29 x 10 15 Hz

Mass of an electron 9.1 x 10-28 g

Mass of a proton 1.67 x 10-24 g h = 6.63 x 10 -34 J. s/photon

Mass of a neutron 1.67 x 10-24 g c = 3.0 x 10 8 m/s

R = 8.31 J /K-mole R = 0.082 L.atm/K-mol

E = hn E= hc/l 1 deciliter = 0.1 liter

Q = (Cp)(mass)(DT) PV = nRT

v_rms = 1 atmosphere = 760 mm Hg= 101325 Pa

Density of water (25°C) 1 g/cm3 Specific heat capacity of water 4.18 J/g °C

NAME____________________________

Indicate whether the quantity in Column A is greater than (>), equal to (=), or less than (<) the quantity in column B. You may write the words, the symbols or both. No partial credit will be awarded on the parts of this Problem.

Problem 2 (20 points)

The metabolic breakdown of glucose, C₆H₁₂O₆, in our bodies produces CO₂ which is expelled from our lungs as gas as shown in the equation below.

C₆H₁₂O₆ (s) + O₂ (g) - ‡ H₂O (l) + CO₂ (g).

a) Calculate the volume of dry CO₂ produced at body temperature, 37°C and 1.00 atmosphere when 5.00 grams of glucose is consumed in the reaction.

The structure of glucose is shown below. Some carbons and O-H bonds are not explicitly shown.

b) Each carbon has tetrahedral_____geometry and ________sp3_______hybridization.

1. This molecule is highly soluble in water because water can hydrogen bond to it.

Draw two different ways in which H₂O can hydrogen bond to glucose.

Which bonding theory best explains the observations below?

Place the Letter of the correct answer after each statement.

A. Lewis Diagrams/Octet Rule alone provide satisfactory explanations

B. VSEPR--Valence Shell Electron Pair Repulsion Theory and Lewis Diagrams/Octet Rule

C. No other theory is satisfactory so Molecular Orbital Theory is needed.

1) Magnesium oxide exists as an ionic salt ______A________

2) Molecular oxygen is paramagnetic _______C________

3) The length of the C-Cbond in benzene, C₆H₆, is intermediate between that in C₂H₆ and C₂H₄___A or B___

4) Carbon frequently forms four single bonds_____A__

5) Ozone, O₃, is a polar molecule______B_____

6) There is only one structure for CH₂Cl₂ (no isomers exist)_____B____

7) Graphite is a flat two dimensional network of carbons whereas diamond is a three dimensional carbon network.____________B__

8) C₂ does not have a quadruple bond__________C________

Global warming and its possible relationship to the production of CO₂ gas were discussed during international negotiations in Kyoto, Japan in 1997.

(a) It has been estimated that the US will dump 1480 metric tons of carbon into the air in the form of carbon dioxide in 1997 as a result of the combustion of carbon based fuels. Calculate the mass of CO₂ in kilograms that will be emitted into the atmosphere by the US this year. One metric ton equals 1000 kilograms.

2. The combustion of glucose (C₆H₁₂O₆) produces carbon dioxide as well. If each person ate the equivalent of 500 grams of glucose per day, calculate the amount of carbon dioxide (in kilograms) being emitted into the atmosphere per year by humans merely breathing. [Useful information: There are approximately 5.5 billion people in the world. A year is 365 days.]

A. Some of the molecules below resemble each other because they are resonance hybrids or isomers. Circle the correct underlined choice. Please note that not all carbons and hydrogens are shown explicitly. You may want to add these atoms.

B. Isomers are molecules which have the same molecular formula but different structures=>>><4.24 Liters t

Resonance hybrids are molecules which have the same__ structures=>>><4.24 Liters t _____________ but different__bonding/location of electrons____________.

Circle the correct choice resonance hybrids or isomers

All resonance hybrids or isomers for a given molecule are resonance hybrids or isomers but

different resonance hybrids or isomers are not resonance hybrids or isomers.

3. Several Lewis Structures for BF₃ are shown below. Discuss the merits and defects of each structure in terms of formal charges and the octet rule. What experimental data could be used to figure out the "true" structure?

The arsenic in a 1.22 gram sample of a pesticide was converted to AsO₄^3- by suitable chemical treatment. It was then titrated using Ag⁺ to form Ag₃AsO₄ as a precipitate. If it took 25.0 mL of 0.102 M Ag⁺ to reach the equivalence point in this titration, what is the mass percentage of arsencic in the pesticide?

Are these optimal hydrogen bonds? If so, write "yes", otherwise state what is wrong and suggest a remedy.

1. No, the C-H bond is not polar
2. Yes
3. No, the two F's should be in a straight line.

B. Hemoglobin is a protein which transports oxygen from the lungs to the tissues. It is polymer composed of a chain of amino acids which is folded into a globular structure. Normal hemoglobin contains a glutamic acid residue at position 6 and this hemoglobin is soluble in water. Hemoglobin S is a variant which contain a valine at position 6. Hemoglobin S is less soluble in water and Hemoglobin S molecules have a tendancy to stick together to form long protein chains. Red blood cells containing these Hemoglobin S chains have a sickle shape instead of the normal spherical shape. The net result of this glutamic acid to valine mutation is a condition called sickle-cell anemia, the first molecular disease to be discovered.

3. Based on the two structures below, show how water can interact more strongly with the Hemoglobin bearing glutamic acid.
4. Suggest a reason why the Hemoglobin S proteins stick together.

Problem 8 (10 points).

To the great surprise of all the Physicists and Chemists on Earth a space probe returns to Earth in the year 2132 with samples from a universe where electrons can have one of three spin quantum numbers , up, down, or sideways. Of course here our electrons have an m_s value of +1/2 or -1/2. Suppose that the Pauli Exclusion Principle still works, that is each electron in an atom has a set of four unique quantum numbers.

a) How many electrons can be accommodated in the n=1, l=0, m_l=0 subshell?

b) What is the electronic configuration and atomic number of the first inert Noble gas? (Having the same properties as Helium)

3. What is the electronic configuration and atomic number of the second inert Noble gas? (Having the same properties as Neon)

1s3 2s3 2p9 atomic number 15

Problem 9 (20 points)

One form of elemental sulfur exists as S₈ and is an insulating yellow solid at Standard Temperature and Pressure. Each molecule is a ring which resembles a crown.

a) What is the electronic configuration of an atom of sulfur?

 

1s2 2s2 2p6 3s2 3p4

b) Draw a Lewis structure for S₈ in which the octet rule is satisfied.

 

Draw 8 S's in a circle. Each S makes 2 single bonds and has 2 lone pairs.

 

 

c) In one sentence describe the bonding and lone pair geometry around each S atom.

 

Tetrahedral electron pair geometry and bent molecular geometry.

 

d) Describe any intermolecular forces between sulfur molecules.

 

Only London Dispersion Forces between 2 S8 molecules.

 

PROBLEM 10 (20 points)

Calculate the volume of oxygen gas released by 5.0 mL of a 2% hydrogen peroxide solution whose density is 1.01 g/mL. You may assume that the reaction below goes to completion during the disinfection process. You may assume 1.00 atm and 25.C °C

2 H₂O₂ (aq) ‡ 2 H₂O + O₂ (g)

 

Volume = ___36 mL__________

 

Problem 11 (to be completed after finishing the rest of the exam) Worth only 10 puny points.

4. What is your favorite formula or molecule? Explain why in two sentences or less.

2. By virtue of your good grades in Chemistry 103/4, you are invited to join the staff of the Chemistry Clinic next year. What advice would you give a confused, but ambitious freshman who did poorly on her first exam?