Much of this final examination in General Chemistry I is about some common acids. We will discuss larg e -ly organic acids because you find these compounds in many foods. With your study of chemistry thissemester you will be able to interpret some of the pro p e rties of these molecules.

1 . (17 points) Vitamin C, C6H8O6, is a common acid.

( a ) The empirical f o rmula of vitamin C is _______________

( b ) The molar mass of vitamin C is

( i ) 176.12 g/mol ( i i i ) 104.1 g/mol

( i i ) 168.1 g/mol ( i v ) 80.12 g/mol

( b ) The weight percent of carbon in vitamin C is

( i ) 8 9 . 9 4 %

( i i ) 6 9 . 2 2 %

( i i i ) 4 2 . 8 7 %

( i v ) 4 0 . 9 2 %

( c ) The approximate values of the three bond angles marked in

the stru c t u res to the right are :

A = _________ B = __________

C = _________

( d ) If you have exactly 100 mg of the acid in a vitamin tablet,

you have

( i ) 5.68 x 10- 4 m o l

( i i ) 0.568 mol

( i i i ) 0.00124 mol

( i v ) 0.595 mol

( v ) none of the above

( e ) Suppose you have a 0.15 M solution of vitamin C. If you dilute 5.0 mL of the solution with

water to give a new solution with a total volume of 25.0 mL, the concentration of vitamin C in

the dilute solution is

( i ) 0.030 M

( i i ) 0.075 M

( i i i ) 0.15 M

( i v ) 0.75 M

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C

C

C

O

O

C

CO

O

C

H O

O

HH

H

H

H H

H

Vitamin C, ascorbic acid (with three bond angles marked)

A

B

C

A

B

C

2 . (17 points) Acetic acid, CH3C O2H, can be pre p a red by fermentation, but the modern method ofp reparing it in large quantities is the catalyzed reaction of methanol, CH3OH, and CO. (See C h e m i s t ry& Chemical Reactivity, page 722.)

( a ) If you combine 1000 g of CH3O H (molar mass = 32.0 g/mol) and 1000 g of CO (molar mass =28.0 g/mol), the theoretical yield of acetic acid (molar mass = 60.05 g/mol) is

( i ) 1000 g

( i i ) 1877 g

( i i i ) 2145 g

( i v ) 2000 g

( b ) Suppose the theoretical yield of acetic acid from the reaction above is 1250 g. However, the re a c-tion actually produces only 926 g. The percent yield of acetic acid is

( i ) 1 3 . 5 %

( i i ) 5 0 . 0 %

( i i i ) 7 4 . 1 %

( i v ) 8 1 . 0 %

( c ) What is the standard molar enthalpy change for the re a c t i o n

C H3O H (l) + CO(g) → C H3C O2H (l)

[ ∆ H ̊f for CH3C O2H = -484.5 kJ/mol. The other enthalpies of formation are found in the text-b o o k . ]

( i ) ∆ H ̊rx n = -135.3 kJ

( i i ) ∆ H ̊rx n = -356.3 kJ

( i i i ) ∆ H ̊rx n = -612.7 kJ

( i v ) ∆ H ̊rx n = -833.7 kJ

( d ) The acetic acid molecule has ______________ valence electro n s .Place any additional electron pairs into the framework here togive the final Lewis electron dot stru c t u re of the acid.

The H—C—H angle is ___________ , the O—C—O angle is

___________. and the C—O—H angle is _________________.

CH3OH + CO CH3CO2H

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C C

O

O

H

H

H

H

3 . (3 points) Acid-base reactions have played a prominent role in this course. In one laboratory experi-ment you found the molar mass of an unknown acid. Suppose you know that your “unknown” acid iscitric acid and that it has the general formula H3A. That is, it has three H+ ions that can react withOH- ions in sodium hydroxide according to the equation

H3A ( a q ) + 3 NaOH(aq) → N a3A ( a q ) + 3 H2O (l)

What is the molar mass of citric acid (re p resented here by H3A) if 0.953 g of the acid re q u i re 30.83mL of 0.483 M N a O H ?

( a ) 64.0 g/mol

( b ) 128 g/mol

( c ) 192 g/mol

( d ) 256 g/mol

( e ) none of the above

4 . (14 points) A salt of citric acid (see question 3 above), gallium citrate, is used in medicine as a diag-nostic tool. The salt is made with radioactive Ga3 + i o n .

( a ) What is the electron configuration of gallium, Ga? (Give this configuration using the orbital boxn o t a t i o n and the noble gas abbre v i a t i o n. )

( b ) What is the electron configuration of the gallium(III) ion, Ga3 +? (Give this configuration using thes p e c t roscopic notation and the noble gas abbre v i a t i o n. )

( c ) The isotope of gallium used in medicine is 6 7Ga. This isotope has _____________ protons and

_____________ neutrons in the nucleus.

( d ) As a Group 3A element, gallium chemistry is like that of aluminum. Thus, gallium chloride re a c t s

with sodium hydroxide to give Ga(OH)3. Balance the equation.

_ _ _ _ _ G a C l3 + _____ NaOH → _ _ _ _ _ _ G a ( O H )3 + ______ N a C l

The reaction is a ( re d o x ) ( a c i d - b a s e ) ( p re c i p i t a t i o n ) reaction. ________________________

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5 . (12 points) Benzoic acid (C6H5C O2H, molar mass = 122.1 g/mol) is found in nature and its sodiumsalt is often found in soft drinks. The acid can burn in air according to the equation

2 C6H5C O2H ( s ) + 15 O2(g) → 14 CO2( g ) + 6 H2O (l)

( a ) If 3.00 g of benzoic acid burns, what quantity of O2 is re q u i red for complete re a c t i o n ?

( i ) 3.00 O2 g

( i i ) 5.90 O2 g

( i i i ) 11.8 O2 g

( i v ) 32.4 g O2 g

( b ) What quantity of CO2 is produced from the combustion of 3.00 g of benzoic acid?

( i ) 0.154 g CO2

( i i ) 1.08 g CO2

( i i i ) 7.57 g CO2

( i v ) 15.1 g CO2

( c ) The combustion of benzoic acid is used to calibrate calorimeters. What is the enthalpy change forthe reaction of benzoic acid with O2? [∆H˚f for solid benzoic acid = -385.2 kJ/mol]

( i ) ∆ H ̊rx n = -294.1 kJ

( i i ) ∆ H ̊rx n = +294.1 kJ

( i i i ) ∆ H ̊rx n = -6453.4 kJ

( i v ) ∆ H ̊rx n = +6453.4 kJ

( v ) ∆ H ̊rx n = -8288.3 kJ

( d ) Specify the approximate values for the following bond angles in benzoic acid:

A = __________

B = __________

C = __________

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••

C

CC

C

C C

C

H

H

H H

O

O

H

H

••

••••

A

B

C

6 . (10 points) One way to analyze a mixture for vitamin C content is to titrate the vitamin C, ascorbicacid, with bromine to give dehydroascorbic acid, C6H6O6.

C6H8O6(aq) + B r2(l) → C6H6O6(aq) + 2 H+(aq) + 2 Br-( a q )

( a ) Is this reaction a ( re d o x ) ( a c i d - b a s e ) ( p re c i p i t a t i o n ) re a c t i o n ? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

( b ) The reaction produces the bromide ion. Give the electron configuration using the s p e c t ro s c o p i cn o t a t i o n (and the noble gas abbre v i a t i o n if you wish) of the b romide ion.

( c ) To analyze a mixture of substances, one of which is vitamin C, you titrate a 1.035 g sample withB r2. If you use 35.20 mL of 0.1025 M aqueous Br2 in the titration, what is the weight percent ofvitamin C (176.12 g/mol) in the 1.035 g sample? Show your work completely and care f u l l y !

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7 . (6 points) Maleic acid is a very important industrial chemical. Hundreds of thousands of tons are madeper year. It is used in plastics for bathrooms and car bumpers, additives for vinyl flooring and mouth-washes, and in artificial sweeteners, among other things.

( a ) If you wish to pre p a re 5.00 x 102 g of maleic acid (C4H6O4), what quantity of butane (C4H1 0)would be re q u i re d ?

( i ) 13.7 g C4H1 0 re q ’ d

( i i ) 118 g C4H1 0 re q ’ d

( i i i ) 246 g C4H1 0 re q ’ d

( i v ) 500 g C4H1 0 re q ’ d

( b ) An intermediate in the maleic acid reaction is maleic anhydride, C4HxOy. To find its form u l ayou burn a sample in air. In such an experiment you discover that 1.056 g of maleic anhydridegives 1.602 g of CO2 and 0.328 g of H2O. What is the molecular formula for maleic anhydride?

C4HxOy(s) + some O2(g) → 1.602 g CO2( g ) + 0.328 g H2O ( g )

( i ) C4H4O4

( i i ) C4H4O6

( i i i ) C4H4O8

( i v ) C4H6O6

8 . (3 points) The combustion of butane, C4H1 0, is exothermic; 1 mol of C4H1 0 p roduces 2657 kJ ofheat energ y. What quantity of butane (molar mass = 58.1 g/mol) must be burned to raise the temper-a t u re of 250 g of cold water (5.0 ˚C) to 65 ˚C?

( i ) 0.0236 g C4H1 0

( i i ) 1.37 g C4H1 0

( i i i ) 2.66 g C4H1 0

( i v ) 6.28 g C4H1 0

H2C

H2C

C C

OO

OHHO2 C4H10(g) + 7 O2(g) + 6 H2O(g)

maleic acid

••

•• •• •• ••

••

••

••2

butane

(s)

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8 . (28 points) Lewis electron dot stru c t u res.

( a ) Draw a Lewis electron dot stru c t u re for the simple acid HOCN. (The atoms lie in a chain in theo rder given.)

Number of valence electrons in HOCN = _______________________

( b ) F o rmic acid is the simplest organic acid. It reacts with a base to give the formate anion, HCO2-.

Number of valence electrons in formate anion = _______________

Lewis electron dot stru c t u re of HCO2-, including all relevant resonance stru c t u re s .

The electron pair geometry around the C atom is ___________________________________

( c ) The acid HNO3 is an important acid. Its name is ____________________________

A Lewis electron dot stru c t u re for HNO3 is illustrated here.

( i ) The electron pair geometry around the N atom is

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

( i i ) F o rmal charg e s :

O atom 1 = __________ O atom 2 = __________

O atom 3 = __________ N atom = __________

( i i i ) H—O—N bond angle = __________

O — N —O bond angle = __________

Draw any other resonance stru c t u res for HNO3.

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NO O

O

••

••••

••

••

••

••H

O atom 1 O atom 2

O atom 3

9 . (24 points) Sulfur is ubiquitous in our environment and in chemical and biological systems. It form smany diff e rent types of compounds. For example,

Ti4 +(aq) + 2 H2S(aq) → Ti S2(s) + 4 H+( a q )

( a ) This reaction is a ( re d o x ) ( a c i d - b a s e ) ( p re c i p i t a t i o n ) reaction. ________________________

( b ) Titanium has an extensive chemistry, forming both Ti2 + and Ti4 + cations. Using the orbital boxn o t a t i o n (and the noble gas abbre v i a t i o n), show the electron configuration for Ti2 +.

Is the Ti2 + ion paramagnetic or diamagnetic? _____________________________

( c ) Ti S2 contains the sulfide ion. Using the orbital box notation (and the noble gas abbre v i a t i o n), showthe electron configuration for the sulfide ion.

( d ) Sulfur forms a broad range of covalent compounds with halogens.

( i ) Draw the Lewis electron dot stru c t u re for SO2.

The electron pair geometry of around S in SO2 is __________________________. The molecular

g e o m e t ry of SO2 is _____________________________ and the approximate O—S—O bond angle is

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

( i ) Draw the Lewis electron dot stru c t u re for OSF4.

The electron pair geometry of around S in OSF4 is ______________________________________.

The molecular geometry of OSF4 is ____________________________________ and an appro x i m a t e

F—S—F bond angle is _____________________ (indicate on your drawing which bond angle you

refer to).

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1 0 . (16 points) Periodic pro p e rt i e s

( a ) Place the following elements in order of increasing size: Al, F, S, P

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _smallest size l a rgest size

( b ) Of the elements Al, F, S, and P, which has the highest electron aff i n i t y ? _ _ _ _ _ _ _

( c ) Of the elements Al, F, S, and P, which has the lowest ionization energ y ? _ _ _ _ _ _ _

( d ) Considering the elements Al, F, S, and P, which of the following ions are NOT likely to form ?

( C i rcle all that apply.)

A l4 + F- S3 - P5 + P3 -

( e ) Does F have an electron assigned to a 4p orbital? _ _ _ _ _ _ _ _

( f ) Al has an electron with a set of quantum numbers n = 3, l = 1, ml = 1, and ms = +1/2. To what

type of orbital is this electron assigned (give letter designation)? _____________. Sketch a picture

of the boundary surface of such an orbital.

Draw the electron configuration of Al [using the orbital box notation and the noble gas abbre v i a -

t i o n] and draw an arrow pointing to the electro n that has the set of quantum number n = 3, l = 1,

ml = 1, and ms = +1/2

1 1 . (1 point) Give us your favorite holiday recipe. What is your favorite holiday food?

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