dlrc chemistry 16 comprehensive samplex for long exam 2

1 | D L R C C h e m 1 6 L E 2 S a m p l e x

Chemistry 16 Comprehensive Samplex for Long Exam 2

September 7, 2012

Instructions: Answer as many items as you can. Read each question carefully and answer honestly. All

information you need is in this paper. Good luck!

I. MULTIPLE CHOICE. Choose the letter corresponding to the best answer.

1. Which of the following set of quantum

numbers is possible?

A. n=1, l=0, ml=1, ms=1/2

B. n=5, l=3, ml=-2, ms=-1/2

C. n=2, l=1, ml=0, ms=0

D. None of these

2. Two electrons in the same atom which have

identical values of quantum numbers l and

ml are said to be in ___

A. The same shell and subshell but in

different orbitals

B. Same shell but different subshells and

orbitals

C. Same shell, subshell and orbitals

D. Same subshell and orbitals but different

shells

3. For systems with positive changes in

enthalpy and entropy, processes become

spontaneous at __

A. All temperatures

B. Low

C. High

D. Absolute zero

4. Which of the following is a polar molecule?

A. RbCl

B. BF3

C. CCl4

D. PCl3


5. Which of the following is false about the

structure of thiocyanate ion?

A. The C-N bond is a double bond.

B. There are no lone pairs on C.

C. There is a lone pair of electrons on N.

D. The C-H bond is a single bond.

6. Of the following, which is a state function?

A. ∆H

B. q

C. w

D. All of the above

7. The shorter the internuclear distance

between two bonded atoms, the

A. Less energy needed to break the bond

B. Less multiple bonding character there is

C. More resonance

D. More energy needed to break the bond

8. Which of the following is an unstable species

and is bound not to exist?

A. H2

B. He2+

C. Be2+

D. Be2

9. Which of the following pairs have similar

molecular geometry?

A. CH3+, CH3

-

B. PF5, ClF5

C. H2O, NH2-

D. None of these

10. Which of the following ions has the largest

atomic radius?

A. Na+

B. Mg+

C. O2-

D. F-

11. Which of the following atoms has the largest

first ionization energy?

A. Rb

B. Sr

C. Al

D. All have same magnitude of energy.

12. What is the correct electronic configuration

for a nickel atom?

A. 1s22s22p64s23d23d23d23d13d1

B. 1s22s22p6 3s2 3p6 4s2 4p63d13d1

C. 1s22s22p63s23p63d10

D. none of these

13. The Lewis structure for calcium hydride is

A. [H:]-[Ca]2+[H:]-

B. [H:]-[Ca] +

C. H-Ca-H

D. Ca-H

14. Which of the following is best represented by

a set of resonance structures?

A. Ammonium

B. Methane

C. Oxygen difluoride

D. Sulfur dioxide

15. What is the formal charge on N in nitrate

ion?

A. 2

B. 2-

C. 1

D. 1-

16. If there is a negative change in the Gibb’s

energy, then the reaction is said to be ___.

A. Reversible

B. Spontaneous

C. Exothermic

D. Endothermic

17. In the experiment on Corrosion, the portion

of the nail that was oxidized was ___ in color

and acted as the __.

A. White, anode

B. Pink, anode

C. Blue green, cathode

D. Blue green, anode

18. In the experiment on Corrosion, zinc acted

as the __ while the nail is the __

A. Protected Anode; Sacrificial Cathode

B. Protected Cathode; Sacrificial Anode

C. Sacrificial Cathode; Protected Anode

D. Sacrificial Anode; Protected Cathode

19. Which of the following reactions is non-

spontaneous?

A. Neutralization of NaOH and HCl

B. Freezing water in room temperature

C. Combustion of octane fuel

D. None of the above

20. Which of the following statements is false?

A. Ferrous hydroxide is formed by adding

soluble Fe3+ sample to NaOH or NH3.

B. Calcium will not precipitate to limiting and

excess ammonia.


C. A Prussian blue precipitate will form

when Fe2+ is added to potassium

ferricyanide.

D. The formula of the brown ring in the

nitrate test is [Fe(NO)]2+.

21. Which of the following ionic compounds has

the highest entropy?

A. Calcium chloride

B. Magnesium arsenate

C. Sodium oxalate

D. Tin(IV) oxide

For numbers 22-26, refer to the structure of

capsaicin below:

22. The EGG, MGG, and hybridization of O1 is:

A. Tetrahedral; angular; sp2

B. Trigonal planar; trigonal pyramidal; sp3

C. Tetrahedral; angular; sp3

D. Trigonal planar; angular; sp2

23. The difference/s between C2 and C5 is:

A. Their EGG and hybridization

B. Their MGG and hybridization

C. Their EGG and MGG

D. Their EGG, MGG, and hybridization

24. How many σ and π bonds are in capsaicin?

A. 43 ; 5

B. 42 ; 4

C. 42 ; 5

D. 43 ; 4

25. What is the hybridization overlap in O4?

A. sp2 – sp3

B. sp3 – sp2

C. sp2 – sp2

D. sp3 – sp3

26. The formal charge of N3 is __ and the

hybridization overlap in C – N3 – C is __.

A. 0; sp2-sp3-sp2

B. 0; sp3-sp3-sp2

C. +1; sp3-sp3-sp2

D. +1; sp2-sp3-sp2

27. Which of the following is true?

A. Manganese(II) cations are dominant in

basic medium.

B. When organic chlorine and iodine are

combined in a toluene-water mixture,

there will be no visible reaction.

C. A more acidic medium promotes

corrosion of metals.

D. Zinc, Nickel, and Cobalt can act as

sacrificial anodes for Iron.

28. What is the net heat change if 25.0 mL of

3.78 M sulfuric acid is neutralized by 50.0

mL of 1.90 M potassium hydroxide?

A. -5.27 kJ

B. 5.27 kJ

C. 5.30 kJ

D. -5.30 kJ

29. What is the De Broglie wavelength and

frequency of a photon with mass 1.08×10-24

nanograms?

A. 2.05×10-7 m; 1.47×1014 s-1

B. 2.05×10-6 m; 1.47×1015 s-1

C. 2.05×10-6 m; 1.47×1014 s-1

D. 2.05×10-7 m; 1.47×1015 s-1

30. If the uncertainty for a velocity of a photon is

3.14×10-15 m/s, given that the mass of the

photon is 7.09×10-9 kg, what is the

uncertainty of the position of the photon?

A. 2.37×10-12 m

B. 2.63×10-12 m

C. 2.86×10-12 m

D. 2.45×10-12 m

31. Nitrogen gas and Hydrogen gas react to

form ammonia gas. Given that ∆Hf of

ammonia is -46.3 kJ, how many grams of

ammonia are produced if 176.7 kJ of heat is

released?

A. 65.0 g

B. 130.0 g

C. 7.63 g

D. 3.81 g

32. Which ion/s can give an interfering false ring

for nitrate test?

A. Thiocyanate only

B. Ammonium and thiocyanate

C. Thiocyanate, Bromide, Iodide

D. Sulfate, Bromide, Thiocyanate


II. MODIFIED TRUE OR FALSE. Write TRUE if the statement is true. Otherwise, determine what part of

the statement made it false and offer corrections.

1. In the ozone layer, O3(g) absorbs harmful UV radiation and forms oxygen gas and gaseous oxygen

atom. The entropy change for this process is equal to zero.

2. The 4f orbitals can accommodate a maximum of 10 e-.

3. Hess’s Law is a consequence of the first law of thermodynamics.

4. On a humid day, we can observe water vapor to condense along the outer wall of cold drink bottles.

The formation of the vapor is an endothermic process.

5. The form of carbon with a ∆Ho formation value of zero is diamond.

6. The azimuthal quantum number tells us how far from the nucleus an electron is.

7. The oxidation state assigned to P in the phosphate ion is +5.

8. In the aluminum atom, the outermost electron has the quantum numbers n=3, l=1, ml=1, and ms=+1/2.

9. qsoln is still part of qcal even if the volumes of the solution used for calibration and calculation are not

constant.

10. XeO2F2 has a trigonal bipyramidal electron group geometry, and a square pyramidal molecular group

geometry.

11. Naphthalene, C10H8, is made up of two benzene rings “stacked” or “glued” together. The number of

dominant resonance structures of naphthalene is two.

12. The order of hydrohalidic acids’ ionic character in increasing order is: I < Br < Cl < F.

13. Prussian blue precipitate from potassium ferricyanide indicates the presence of Fe3+ ions, while from

potassium ferrocyanide indicates the presence of Fe2+ ions.

14. The net dipole moment of water explains sodium chloride’s miscibility in it.

15. In excess ammonia, Zn2+ will form a colorless complex [Zn(NH3)2]2+, while in excess NaOH, Zn2+ will

form a colorless complex [Zn(OH)4]2-.

16. Nitrate ion does not exhibit pi bond delocalization.

17. Adding potassium ferricyanide to Zn2+ will form yellow precipitate KZn[Fe(CN)6], while adding potassium

ferrocyanide will form white precipitate KZn3[Fe(CN)6].

18. There will be an exothermic change in heat if the system gives off heat to the surroundings, and the

surroundings does work to the system.

19. An exothermic reaction from low entropy to high entropy will only proceed at high temperatures.

20. If a reaction is endothermic from high entropy to low entropy, the reverse reaction is non-spontaneous.

III. CAUSE AND EFFECT. Determine the effect of the cause stated in the first column on the parameter in

the second assuming all other variables are held constant.

Effects: Increase, Decrease, No Effect

Cause Parameter Effect

1. Actual molarity of the acid is greater than the recorded value.

Magnitude of calculated ∆H

2. The cylinder used for measuring the base solution was wet.

3. The student pulled the thermometer out of the set-up to take temperature readings.

4. There is a tiny hole in the cork, exposing the inside of the calorimeter. Magnitude of

calculated Ccal

5. Actual molarity of the base is greater than the recorded value.


Effects: Becomes present, Becomes absent, No Effect (stays the same)

Cause Parameter Effect

6. Mossy Zinc and Aluminum metal were accidentally coiled together with iron nail.

Corroded Zinc

7. Gelatin mixture was accidentally added with concentrated NaOH

Appearance of Prussian blue (after 1 day)

8. KMnO4 was accidentally added in excess.

Persistence of Pink Color

9. Litmus paper was accidentally dipped into unknown solution with NaOH.

Indication of gaseous ammonia

10. Copper(II) nitrate was added with NaOH, then with excess ammonia.

Dissolution to deep blue complex

11. Bromide sample was accidentally contaminated with iodide sample for KMnO4 elimination test.

Pink-red toluene layer

Yellow toluene layer

IV. PROBLEM SOLVING. Read (without underestimation) the problems carefully, and solve for what is

asked. There are ten problems in this part of the review.

Problem 1: Lead-Acid Battery

The lead-acid battery, invented in 1959 by French physicist Gaston Planté, is the oldest model of

rechargeable batteries. Lead-acid batteries are normally used in automobile engines, because it can generate

large amounts of current for short periods of time.

When a lead-acid battery is fully charged, the battery contains sulfuric acid as the electrolyte. Two

grids, lead grid and lead(IV) oxide grid, serve as the electrodes of the battery. During discharge, the grids are

converted to lead(II) sulfate, and when the battery is fully discharged, the sulfuric acid is almost diluted to

water. Assume that sulfuric acid does not fully ionize during discharge; it will only give one H+ during ionization.

a) WRITE the balanced half-reactions for the anode and the cathode. INDICATE the reducing and

oxidizing agents.

b) WRITE the overall balanced equation for lead-acid battery discharge.

c) CALCULATE the number of electrons loss/gained after full discharge if 150.0 g of solid lead, 150.0 g

lead(IV) oxide, and 3.00 L of 4.2 M sulfuric acid was present at full charge.

The problem with lead-acid batteries is its environmental risks. Even though lead-acid batteries are

rechargeable, lead can still escape from the battery, especially during battery explosion. A battery explosion

happens when water molecules hydrolyze to hydrogen and oxygen gas during recharging.

d) WRITE the balanced equation for the hydrolysis of water.

An explosion can spray battery acid and release harmful lead compounds in the environment. Lead

mostly accumulates in bodies of water in the form of lead(II) ions. To detect concentration of lead(II) ions in

bodies of water, chemists use cerimetry, a redox titration by using cerium(IV) ions as the titrant.


50 mL of a wastewater sample near a lead-acid battery explosion site was acidified with 25 mL 6 M

HCl, and was titrated with 32.6 mL of cerium(IV) sulfate solution. The cerium(IV) sulfate solution was prepared

dissolving 250 g of the solid in 800 mL distilled water.

e) If lead(II) and cerium(IV) becomes lead(IV) and cerium(III) during titration, WRITE the balanced

equation of the redox reaction.

f) CALCULATE the concentration of lead(II) ions in the wastewater sample.

Problem 2: Bomb Calorimetry

A more sophisticated calorimeter than the constant-pressure (coffee cup) calorimeter is the bomb

calorimeter. The bomb calorimeter uses an insulated sealed vessel where the reaction (with the sample) takes

place. The vessel is pressurized with excess oxygen gas and it is placed inside the calorimeter full of water.

Electric current will run through the vessel, igniting the sample. A thermometer will then measure the

temperature change by contact with the water inside the calorimeter. Bomb calorimetry is used mostly in

calculating energy needed to burn food or fuel.

a) The bomb calorimeter is also known as “constant-volume” calorimeter, because reactions are carried

out at constant volume. EXPLAIN why ∆E corresponds to the transferred heat in bomb calorimeter

rather than ∆H.

The bomb calorimeter is calibrated by burning 25.0 g of solid glucose (C6H12O6) in the sealed vessel,

and the temperature rose from 25.00 °C to 59.50 °C. The heat of reaction for the combustion of one mole of

solid glucose is -2803 kJ.

b) WRITE the balanced equation for the combustion of solid glucose.

c) CALCULATE the heat capacity of the bomb calorimeter.

A certain milk tea was found to contain fructose (C6H12O6), gallic acid and palmitic acid. Gallic acid (MW

= 170.12 g/mol) is an antioxidant found in most Chinese herbs, while palmitic acid (C16H32O2) is an

unsaturated fat found in dairy products. 100.0 mL of the sample (filtered, only containing the desirable

compounds) was burned in the sealed vessel of the calorimeter in an initial temperature of 25.00 °C. Several

experiments were conducted to find the percent volumes of some of the compounds and the amount of

products formed.

The following data were collected before and after the tests:

Final Temperature 27.24 °C Density of fructose 1.694 g/mL

Percent volume of fructose 0.400% Density of palmitic acid 0.853 g/mL

Percent volume of palmitic acid 0.200% Density of gallic acid 1.7 g/mL

Percent volume of gallic acid 0.300% Heat of combustion per mole of fructose -2812 kJ/mol

Grams of carbon dioxide 2.385 g Heat of combustion per mole of gallic acid -2655 kJ/mol

Grams of water 0.7604 g

d) CALCULATE the molecular formula of gallic acid.

e) CALCULATE the molar heat of combustion of palmitic acid.

f) WRITE the balanced equations for the combustion of palmitic acid and gallic acid.


[Problem 3]: DLRC-Land

In the year 21XX, scientists discovered a peculiar planet outside Earth, and they named it “DLRC-

Land”. What makes DLRC-Land peculiar is that it defies the laws and theories behind the structure of atoms.

Scientists noticed that the elements in Earth are different compared to the elements in DLRC Land.

Pauli’s Exclusion Principle, Aufbau’s Principle, Hund’s Rule, Heisenberg’s Uncertainty, etc. all apply to DLRC,

except with the quantum numbers. By calculations they concluded that they have the quantum numbers d, lr,

and c.

d corresponds to quantum number n.

lr corresponds to both quantum numbers l and ml. This means lr = 0, ±1, ±2, ±3…± (n-1).

c corresponds to quantum number ms,

The elements in DLRC-Land are named by their atomic number.

a) DRAW the first five periods of the DLRC-Land periodic table based on the information given above

(You just need to draw blocks.)

b) WRITE and DRAW the electronic configuration of DLRC-Land elements 28, 24, and 21. Give the

quantum numbers of their last-entering electron.

c) ARRANGE the following elements by their periodicity. Assume that like elements in Earth, DLRC-Land

elements have their cationic and anionic forms.

a. Atomic Radius: 7-, 162+ 62-

b. Ionization Energy: 2, 9, 13, 14

d) What rules in covalent bonding does DLRC-Land follow if our planet’s elements follow the octet rule

and 18-electron rule? EXPLAIN.

e) INDICATE which of the following hypothetical covalent compounds are possible to exist in DLRC-Land.

If possible, DRAW their Lewis structures and indicate the electron-group geometry and molecular-

group geometry in each central atom.

a. (6)(5)3

b. Hypothetical “carbon chain” (5)2(1)6

c. Hypothetical “carbon chain” (5)3(1)5

d. Hypothetical anion (13)(7)4 -

f) GIVE the hybridized DLRC-Land orbital that corresponds to (a) tetrahedral, (b) trigonal bipyramidal, and

(c) octahedral electron-group geometry.

Problem 4: “Qualitative” Analysis

Dessa Eibaf Conor, a Chem 16 student in UP Diliman, was asked to get 17 reagents from the IC Stock

Room for the qualitative analysis experiment. However, Dessa is a mischievous student, so she removed the

labels of the bottles and replaced them with labels A to Q. Air Asserc, the topnotcher of the 1st Chem 16 LE,

tried to find out the compounds based on her vast knowledge of Chem 16.

These are the results of her tests/observations:

Dessa accidentally placed one drop of L on a tissue paper. The tissue paper acquired a burnt mark.

Based on her lab manual, all fresh (soluble) anionic and cationic samples have molarity of 1.0 M.

When G is added with 5 drops A, a deep red solution formed. When it was added with 5 drops M, a

blue precipitate formed.

When 5 drops of C was added with 5 drops D, a blue precipitate formed, but when mossy zinc was

immersed before adding D, a yellow precipitate formed.


When 5 drops of E was added with 5 drops J, a brown precipitate formed. The precipitate turned

colorless when added with 1 drop of L, but turned green when added with 3 drops of K.

Solid F dissolves into a blue solution when added with L. When added with excess O, the solution

turned deep blue.

Only B and A released a basic gas (by litmus paper test) when added with 2 drops K.

G, N, and P gave a brown ring when the test for nitrate was done.

When 5 drops I was added with 2 drops 0.5 M P, a white precipitate formed, and it dissolved (with

effervescence) in excess Q.

When H was studied for the toluene elimination test, the toluene and aqueous layers turned yellowish-

brown.

When 10 mL I was added with 10 mL G, 0.972 g of brown-orange precipitate formed.

When 5 mL N was added with 1 mL of 6 M K, 0.37 g of white precipitate formed.

When 5 mL H was added with 5 mL of 1.0 M silver nitrate, 0.939 g of precipitate formed.

When 10 mL B was added with 5 mL of 0.5 M P, 1.50 g of white precipitate formed, and it dissolved in

excess organic acid Q.

By records in the stock room, solution I was made by dissolving 73.89 g of it in 500 mL distilled water.

By records in the stock room, solution N was made by dissolving 98.45 g of it in 600 mL distilled water.

After doing the said tests and observations, Air Asserc knew the corresponding compounds from A to

Q. GIVE the corresponding compounds from A to Q. (NOTE: Some of the compounds have slight

modifications from the compounds in the Chem 16 manual. Qualitative analysis alone is not enough to solve

the problem.)

Problem 5: Polynitrogen Chemistry

In 1999, Karl O. Christe and his team of researchers from the Air Force Research Laboratory

synthesized a polynitrogen species other than N2, and azide (N3-). Pentazenium (N5

+), an open chained

“polynitride” like the other compounds, was synthesized for a less toxic and more environmental-friendly

alternative to hydrazine, a gas used in rocket fuel.

a) DRAW the Lewis structures (and resonance structures if possible) for azide anion.

b) DRAW the three most dominant resonance structures of pentazenium. INDICATE the formal charges

of each atom. GIVE the hybridization overlaps between the five nitrogen atoms for each resonance

structure.

Karl Christe proposed a reaction between gaseous hydroazoic acid and N2F+ gas to give pentazenium

and hydrogen fluoride as the byproduct. The bond energies of the atoms are given below:

H – H 432 kJ/mol F – F 159 kJ/mol N = N 418 kJ/mol

H – F 565 kJ/mol F – N 283 kJ/mol N ≡ N 945 kJ/mol

H – N 391 kJ/mol N – N 160 kJ/mol

c) WRITE the balanced equation of the proposed mechanism, using the Lewis structures of the

compounds/ions (instead of writing with chemical formulas).

d) CALCULATE the change in bond enthalpy of the proposed mechanism.

However, a new polynitrogen species is being studied. Pentazole anion, or N5-, is an anion from

aromatic pentazole. Due to its all-nitrogen cyclical structure, chemists have been studying this anion as


another alternative for propellants in space travel, but so far pentazole is known to be unstable and it does not

last longer than a few seconds.

e) DRAW the three most dominant resonance structures of pentazole anion. INDICATE the formal

charges of each atom. GIVE the hybridization overlaps between the five nitrogen atoms for each

resonance structure.

Problem 6: Molecular Orbital Theory

Using Molecular Orbital Theory, PROVE that:

a) Binary (homonuclear) molecules from diamagnetic atoms cannot exist.

b) Charged binary (homonuclear) molecules from diamagnetic atoms can exist.

c) Using your answer in (a), can binary noble gases (Ne2, He2, etc.) exist?

Consider binary fluorine species F2+, F2, and F2

-, and binary boron species B2+, B2, and B2

-. ARRANGE

the groups of species (separately) in increasing order by:

d) Bond Energy e) Bond Length

f) CALCULATE the bond order of all the species. INDICATE their magnetic properties.

Problem 7: Activity of Lanthanum

Lanthanum metal forms cations with a charge of 3+. Consider the following observations about the

chemistry of lanthanum:

When lanthanum metal is exposed to air, a white solid A is formed that contains lanthanum and one

other element.

When lanthanum metal is added to water, gas bubbles are observed and a different white solid B is

formed. Both A and B dissolve in hydrochloric acid to give a clear solution.

When either of these solutions is evaporated, a soluble white solid C remains. If compound C is

dissolved in water and sulfuric acid is added, a white precipitate D forms.

a) PROPOSE identities for the substances A, B, C, and D.

b) WRITE net ionic equations for all the reactions described.

c) Is Lanthanum, in the activity series, above hydrogen or below hydrogen? EXPLAIN.

What you will see below are free energy changes of redox reactions (regardless of spontaneity)

between lanthanum and certain metals:

La(s) + Al3+(aq) → La3+

(aq) + Al(s) -208 kJ/mol 2Al(s) + 3Yb2+(aq) → 2Al3+

(aq) + 3Yb(s) 212 kJ/mol

3Rb+(aq) + La(s) → 3Rb(s) + La3+

(aq) 174 kJ/mol 2Rb(s) + Yb2+(aq) → 2Rb+

(aq) + Yb(s) -42 kJ/mol

3Yb(s) + 2La3+(aq) → 3Yb2+

(aq) + 2La(s) -221 kJ/mol Ti(s) + Yb2+(aq) →Ti2+

(aq) + Yb(s) 218 kJ/mol

3Ti(s) + 2La3+(aq) → 3Ti2+

(aq) + 2La(s) 434 kJ/mol Ti(s) + 2Rb+(aq) → Ti2+(aq) + 2Rb(s) 261 kJ/mol

3Rb(s)+ Al3+(aq) → 3Rb+

(aq) + Al(s) -382 kJ/mol 3Ti(s) + 2Al3+(aq) → 3Ti2+ + 2Al(s) 19 kJ/mol

d) ARRANGE the five elements (in the table) in decreasing reducing property.

e) INDICATE which elements can act as a sacrificial anode for lanthanum.


f) INDICATE which elements will be protected by lanthanum from corrosion.

Problem 8: Permanganometry

Permanganometry is a special redox titration that involves the use of permanganates, and it is an

alternative to acid-base titration because permanganates can transform to different manganese species,

depending on the pH of the solution.

Standardization of KMnO4 is done by oxalic acid as the primary standard (You should know the formula

of oxalic acid, based on inorganic nomenclature.) Oxalic acid was prepared by dissolving 0.63 g of oxalic acid

crystals in 100 mL water. 20 mL of 0.1 M sulfuric acid is added to the oxalic acid solution to acidify the medium.

The results of the standardization are as follows:

Trial Starting Point Endpoint

1 0.0 mL 3.7 mL

2 3.7 mL 7.5 mL

3 7.5 mL 11.0 mL

Organic acids (Acids containing C, H, and O) turn into carbon dioxide gas and water during titration.

a) WRITE the balanced redox equation for standardization.

b) CALCULATE the molarity of KMnO4 in each trial, and the average molarity of KMnO4.

A Chem 16 student wants to find out the amount of Ascorbic Acid (MF = C6H8O6) in a sample of orange

juice. A 25 mL orange juice sample was added with 25 mL distilled water, and was titrated with the KMnO4

solution. While titrating, the analyte slowly turned into a solution with brown precipitate.

Trial Starting Point Endpoint

1 0.0 mL 5.6 mL

2 5.6 mL 11.6 mL

3 11.6 mL 17.0 mL

c) WRITE the balanced redox equation for titration of ascorbic acid.

d) CALCULATE the molarity of ascorbic acid in each trial, and the average molarity of ascorbic acid.

Problem 9: Olympicene

Olympicene (MW = 240.286 g/mol) is a special aromatic compound with five carbon rings stacked

together like a benzene ring. It was recently synthesized by Anish Mistry and David Fox of the University of

Warwick only for the purpose of celebrating the London 2012 Olympics.

1.00 g of olympicene (only containing C and H) was burned in excess oxygen and the combustion

yielded 3.48 g carbon dioxide.

a) CALCULATE the molecular formula of olympicene.


The picture above is the carbon skeletal structure of olympicine. Based on experiments, only Ring 2

cannot undergo pi-bond delocalization.

b) Can Ring 2 have all of its carbon atoms sp2 hybridized? EXPLAIN.

c) GIVE three possible resonance structures of olympicene by assigning the C and H atoms, and double

bonds.

d) GIVE all possible hybridization overlaps in olympicene.

Problem 10: Solvay Process

The Solvay Process, invented by Ernest Solvay in the 1860s, is an industrial process used to make

sodium carbonate, and this chemicals are needed in glass making and oxidizing bleaches. The following

reactions are steps for Solvay Process:

NaCl(aq) + CO2(g) + NH3(g) + H2O(l) → NaHCO3(s) + NH4Cl(s) ∆Hrxn = -129.48 kJ/mol ∆Srxn = -394.81 J/mol*K

CaCO3(s) → CaO(s) + CO2(g) ∆Hrxn = 178.3 kJ/mol ∆Srxn = 160.47 J/mol*K

CaO(s) + H2O(l) → Ca(OH)2(s) ∆Hrxn = -65.17 kJ/mol ∆Srxn =-26.26 J/mol*K

Ca(OH)2(s) + 2NH4Cl(s) → 2NH3(g) + CaCl2(aq) + 2H2O(l) ∆Hrxn = 73.75 kJ/mol ∆Srxn =356.82 J/mol*K

2 NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g) ∆Hrxn = -85.17 kJ/mol ∆Srxn =215.31 J/mol*K

The overall reaction of the spontaneous process is: 2 NaCl(aq) + CaCO3(s) → Na2CO3(s) + CaCl2(aq).

a) CALCULATE the overall ∆Hrxn of the Solvay process.

b) CALCULATE the overall free energy change of the Solvay process in 25 °C

c) If 1324.2 kJ of free energy were released in the process (in excess calcium carbonate):

a. CALCULATE the grams of sodium carbonate synthesized in the process.

b. CALCULATE the grams of sodium chloride used in the process.

dlrc chemistry 16 comprehensive samplex for long exam 2

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