AP Chem FRQ Practice 2009

7/24/2019 AP Chem FRQ Practice 2009

1/12

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n0

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CollegeBoard

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Advanced Placement

Program

AP@

Chemistry

Free-Response

Ouestions

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2/12

r-

r5

N\V

-r--

-J

F>R

,-I

x

-F\o

-E

a

CFrr,

-z:

r,:i

-a

c

tr,4

iaH't

'c

.l

3il^i

O

.^ >:

rl

.)


3/12

ADVANCED

PLACEMENT

CHEMISTRY

EQUATIONS

AND CONSTANTS

ATOMIC

STRUCTURE

E=ltv

c=)-t

t

ntu

l;-

-2.118

x

10-18

joule

EQUILIBRIUM

-

[H-l[A-]

^n

=

_lgAl

_

toH-ltHB+l

tBl

:

tOH-l[H*]

=

1.0 x

lg-la

@

25"C

=KnxKu

-

-log[H+],

pOH

=

-loglOH-l

=pH+pOH

fA-|

=

pAn

t

toctHAi

pOH

=

pKr,

+logl$J

tBl

PK,,

=

-logKn,

pKt,

=

-logK,,

K

t,

=

K,(RT\^"

.

where

Arr

=

moles

product

gas

-

moles reactant gas

E

=

energy

u

=

velocity

i'

=

frequency

n

=

principal

quantum

number

2

=

wavelength

,??

=

mass

p

=

momentum

Speed

of light, c

=

3.0

x

108 m s-l

Planck's

constant,

h

=

6.63x

10-34

J

s

Boltzmann's

constant,

k

=

1.38

x

10-23

J K-l

Avogadro's

number

=

6.022

x

1023

mol-l

Electron

charge,

e

=

-1.602

x

l0-19

coulomb

I

electron volt per

atom

=

96.5

kJmol-l

Equilibrium

Constants

K"

(weak

acid)

K,

(weak

base)

K,

(water)

Kn

(gas

pressure)

K.

(molar

concentrations)

S"

=

standard

entropy

11"

=

standard enthalpy

G'

=

standard free

energy

E"

=

standard

reduction potential

7

=

temperature

lr

=

moles

,7'

=

mass

Q

=

heat

c

=

specific

heat

capacity

Cp

=

molar heat

capacity

at consl.ant pressure

En

=

acti"'ation energy

,t

=

rate constant

A

=

frequency

factor

Faraday's

constant,'5

=

96,500

coulombs per

mole

of electrons

Gas constant,

R

=

8.31J

mol-l

K-L

=

0.0821 L

atm mol-lK-l

=

62.4

L

ton

mol-l K-l

=

8.31

volt

coulonrb rnol-l

K-l

P=ntu

Kh

Ku

pH

1.1

la

pH

THERMOCHEMISTRY/KINETICS

ASo

=

lS'

products

-)S"

reactants

LH

=

t

lH,'

nroducrs

-F

nA;

reacranrs

A.Go

=

>AGf

products

->LCi

reactants

AG"=411"-fAS'

=

-RT

lnK

=

-2.303Rf

logK

=

-n?F

E"

AG

=

AC" + RT lnQ

=

AGo

+

2.303

RT logQ

q

=

lnc\T

AH

Cr=#

ln[A],-ln[A]n

=-11

li

_

_

ut

f

^l

r^l

LAlr

LAlo

lnft

=

_{cl_l+

lnA

fi

\.r/

-4-

GO

ON TO

THE

NEXT PAGE.


4/12

STANDARD REDUCTION POTENTIALS

IN

AQUEOUS SOLUTION

AT 25"C

Half-reaction

E'(V)

F2Q)

+

2e-

Co3*

+

e-

Au3* + 3e-

Cl2(8)+

2e-

O2(g)+

4H+ + 4e

Br2(l)+ 2e-

2Hg2* + 2e-

Hg2*

+

2r-

Ag'+e

Hgr2*

+

2e-

Fe3* + e-

I2$)+ 2e-

Cu+

+

e-

Cn2*

+

2e-

cu2t

+

e-

sn4*

+

2e-

S(s)+

2H*

+

2e-

2H+

+

2e-

Pb2* + 2e-

sn2*

+ 2e-

Ni2+ + 2e-

co2*

+ 2e-

cd2* + 2e-

cr3*

+

e-

Fe2* + 2e-

cr3n + 3e-

zn2*

+ 2e-

2H2O(l)+

2e-

Mn2*

+ 2e-

Al3+

+

3e-

Be2*

+ 2e-

Mg2* + 2e-

Na* +

e-

caz*

+ 2e-

sr2*

+ 2e-

Ba2*

+ 2e-

Rb'+e-

K*

+e-

Cs+

+e-

L1+

+e-

-,

-

2F-

co2*

Au(.r)

2CI_

2H,O(/)

2Br-

Hg22*

Hg(/)

Ag(.t)

2

He(/)

-

)+

l- c-

2r-

Cu(.s)

Cu(s)

Cu*

sn2*

HzS(s)

u2ts)

Pb(.i)

Sn(s)

Ni(.s)

Co(.r)

Cd(.i)

cr2*

Fe(.r)

Crls;

Zn(s)

H2(s)

+

2OH-

Mn(s)

Al(.i)

Be(.i)

Mg(s)

Na(.i)

Ca(.i)

Sr(s)

Ba(s)

Rb(s)

K(.t)

Cs(s)

Li(s)

2.87

1.82

1.50

r.36

t.23

1.07

0.92

0.85

0.80

0.79

0.71

0.53

0.52

0.34

0.15

0.15

0.14

0.00

-

0.13

-

0.14

-0.25

-

0.28

-

0.40

-

0.41

-0.41

-

0.11

-

0.16

-

0.83

-

l.l8

-

1.66

-

1.70

-2.37

-2.71

-2.87

-2.89

-2.90

-2.92

-2.92

-2.92

-

3.05

-)

J

-J

--)

J

-+

-t

J

-)

-)

--)

--)

--)

J

-)

--)

-+

-+

J

)

_?

-+

-)

-+

)

-.)

-t

--)

-,

-+

-)

-)

-+

-J

-3- GO ON TO

THE

NEXT PAGE.


5/12

GASES,

LIQUIDS,

AND

SOLUTIONS

PV

=

nRT

/)\

Ip*[4]


6/12

AP@

CHEMISTRY

FREE.RESPONSE

OUESTIONS

CHEMISTRY

Section

II

(Total

tinre-95 minutes)

Part A

Time-55

minutes

YOU IVIAY USE

YOUR

CALCULATOR

FOR

PART

A.

CLEARLY SHOW

THE METHOD USED AND THE STEPS

INVOLVED IN ARRIVING

AT

YOUR ANSWERS.

It

is to

lour

advantage to do thrs,

since

you

may obtain

partial

credit

if

you

do and

you

will

receive

little

or no credit

if

you

do not. Attention should be

paid

to significant figures.

Be sure

to

rvrite

all

your

answers to the

questions

on the

lined

pages

following

each

question

in

the booklet

with

the

pink

cover. Do

N(fT

write

your

answers

on the

green

insert.

Answer

Questions

I

,

2, and 3. The Section II score

weighting for

each

question

is

20

percent.

l,

Ansrverthefcllowingquestionsthatrelatetothechemistrl'ofhalogenoxoacids.

(a)

Use the information

in

the

table below to answer

part

(a)(i).

Acid

K, at 298 K

HOCI 1.9

r

l0-8

HOBr

2.4

x

10-e

(i)

Which of the two acids is stronger, HOCI

or

HOBr

?

Justify

your

answer

in terms of Kn .

(ii)

Dra'w

a

complete Lewis

electron-dot

diagram for

the acid that

you

identified

in

part

(aXi).

(iii)

Hypoiodous acid

has

the

formula

HOI.

Predict

whether

HOI

is a stronger acid or a weaker acid

than

the acid

that

you

identified in

part

(aXi).

Justify

your prediction

in

terms

of chemical bonding.

(b)

Write the equation for the reaction that occurs between hypochlorous acid and

water.

(c)

A 1.2 M

NaOCI solution is

prepared

by dissolving solid NaOCI in distilled water

at 298

K.

The

hydrolysis

reaction

t)Cl-(aq)

+ H.O(1)

|

HOCI(aq) +

OH-(aq) occurs.

(i)

Write

the equilibrium-constant expression

for

the

hydrolysis reaction

that occurs between

OCI-(aq)

and

HrO(/).

(ii)

Calculate the

value of the equilibrium constant at

298 K for

the

hydrolysis reaction.

(iii)

Cak:ulate the

value

of

IOH-]

in the 1.2 M NaOCI solution at 298 K

.

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7/12

AP@

CHEMISTRY

FREE-RESPONSE

OUESTIONS

(d)

A buffer

solution

is

prepared

by dissolving

some solid

NaOCI

in a

solution

of

HOCI

at298

K,

The

oH of

the

buffer

solution

is

determined

to

be 6.48.

(i)

Calculate

the

value

of

[HrO+]

in the buffer

solurion.

(ii)

Indicate

which

of

HOCI(aq)

or

OCI-(a4)

is

presenr

at rhe

hrgher concenrrarion

in rhe

buffer solution.

Support

your

answer

with

a

calculation.

2.

A student

was

assigned

the task

of

determining

the molar

mass

of

an unknown gas.

The

student

measured

the

mass

of a sealed

843

mL rigid

flask

that contained

dry

air. The

student

then flushed

the f'lask vrith

the

unknown

gas,resealedit,andmeasuredthemassagain.Boththeairandtheunknowngaswere

at23.0"1:and750.torr.

The

data

fbr

the

experiment

are

shown

in

the table

below.

Volume

of

sealed

flask

843 mL

Mass of

sealed

flask

and dry

air

157.70

g

Mass

of

sealed

flask

and

unknown

gas

158.08 g

(a)

Calculate

the

mass, in

grams,

of

the dry

air that was

in the

sealed

flask.

(The

density of

drv air

is l.l8

g

L-l

at

23.0'C

and

750.

ton.)

(b)

Calculate

the

mass,

in

grams,

of the

sealed

flask itself

(i.e.,

if it had

no air in

it).

(c)

Calculate

the

mass,

in

grams,

of

the

unknown gas

that was

added

to

the sealed

flask.

(d)

Using

the information

above,

calculate

the value

of

the molar mass

of

the

unknown

sas.

After

the

experiment

was completed,

the

instructor

informed

the student

that

the unknown

gas

was

carbon

dioxide

(44.0

g

mol-l).

(e)

Calculate

the

percent

error

in the value

of

the molar mass

calculated

in

part

(d).

(f)

For

each

of the fbllowing

two

possible

occurrences,

indicate

whether

it

by itself could

hav,: been

responsible

for

the error in the

student's

experimental

result.

You need

not include

any calculations

with

yorr

ani*...

For each

of the possible

occurrences,

justify

your

answer.

Occurrence

1:

The flask

was

incompletely

flushed

with

CO2(S).

resulting

in

some

dry air

remainin_e

in

the flask.

Occurrence2:

Thetemperatureof

theairwas23.0oC,butthetemperatureof

the COr(g) waslowerthan

the reported

23.0"C.

(g)

Describe

the

steps

of

a laboratory

method that

the student

could

use to

verify

that

the

volurne

of the

rigid

flask

is

843

mL at23.0"C.

You need

not include

any calculations

with

your

answer,

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8/12

AP@

CHEMISTRY

FREE.RESPONSE

OUESTIONS

CH.(s)

+ 2

Cl2(s)

-+

CH,CI2(

B)

+ z HCI(s)

3. Methane

gas

reacts

with

chlorine

gas

to form dichloromethane

and hydrogen chloride, as

represented

by the

equation

above.

(a)

A

25.0

g

:iample of methane

gas is placed in

a

reaction

vessel

containing

2.58

mol

of

Cl2(S).

(i)

Identify

the

limiting reactant

when

the

methane and chlorine

gases

are combined. Justify

your

answer

with

a

calculation.

(ii)

Calculate

the total

number of moles of CHrCl,(g)

in the container after the

limiting

reactant has

been

totally

consumed.

Inttiating most

reactions involving

chlorine

gas

involves

breaking

the Cl-Cl bond,

which

has

a

bond energy

of

242 kJ mol-r.

(b)

Calculate

the amount

of

energy,

in

joules.

needed to

break a single

Cl-Cl

bond.

(c)

Calculate the

longest wavelength of light,

in meters. that can supply the energy

per photon

necessary to

break the

Cl-Cl

bond.

The

followinEl

mechanism has been

proposed

for the

reaction

of

methane

gas

with chlonne

gas.

All species

are

in

the

gas phase.

Step

1

Cl,

e

2

Cl

fast

equilibriunt

Step

2

CH*

+

Cl

-+

CH,

+

HCI

slox,

Step

3 CH.,

+ Cl,

-+

CH.,CI

+

Cl

.fasr

Step4

CH,CI

+Cl +CH,CI,+H

fasr

Step

5

H

+ Cl

-+

HCI

fast

(d)

In the mechanism,

is

CH.CI

a catalyst. or is it an intermediate? Justify

your

answer.

(e)

Identify the order of the

reaction

with

respect

to each

of

the

following

according

to the

mechanism.

In each

case,

justLfy

your

answer.

(i)

CH-'(s)

1ti)

Clr(s)

STOP

lf

you

finish

before time

is

called,

you

may

check

your

work on

this

part

only.

Do

not

turn to

the other

part

of the test until

you

are

told to do

so.

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Board.

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9/12

AP@

CHEMISTRY

FREE-RESPONSE

OUESTIONS

CHEMISTRY

Part

B

Time-40

minutes

NO

CALCULATORS

MAY

BE

USED

FOR PART

B.

Answer

Question 4

below. The

Section

II

score

weighting

for

this

question

is

10

percent.

4'

For

each

of the following

three

reactions,

write

a balanced

equation

in

part

(i)

and

answer

the

question

in

part

(ii)'

In

part

(i),

coefficients

should

be

in

terms

of

lowest whole

numbers.

Assume

that

solytions

are aqueous

unless

otherwise

indicated.

Represent

substances

in solutions

as

ions

if

the substances

are

extensively

ionized.

Omit

formulas

for

any

ions

or

molecules

that are

unchanged

by

the

reaction.

You may

use

the

".pt1,

space

at the

bottom

of the

next page

for

scratch

work,

but

only

equations

that

are written

in

the

answer

bor:es provrded

will

be

sraded.

EXAMPLE:

A

strip

of magnesium

metal is

added to

a solution

of silver(i)

nitrate.

(ii)

Which

substance

is

ox idized

in

the

reaction?

lAn

Lt r*',,t

(i)

Balanced

equation:

Mg

t

,*t'->

Mh"*

r

zr@

(a)

A

sample

of

solid

iron(III)

oxide

is reduced

completely

with

solid

carbon

(ii)

What

is the

oxidation

number

of

carbon

before the reaction.

and

what

is the

oxidation

number

of

carbon

after

the reaction

is

complete?

-

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-9-

Balanced

equation:

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10/12

AP@

CHEMISTRY

FREE.RESPONSE

OUESTIONS

(b)

Equal

volumes of equimolar

solutions

of ammonia

and

hydrochloric

acid are

combined.

(ii)

Indicate

whether the

resultin-e

solution

is

acidic,

basic,

or

neutral.

Explain.

(i)

Balanced equation:

(i)

Balanced equation:

(c)

Solid

mer:ury(Il)

oxide decomposes

as

it

is heated

in an open

test tube in a fume hood.

(ii)

After the

reaction

is

complete,

is

the

mass

of

the

material in

the test tube

greater

than, less than, or

equa:l

to

the mass of

the original

sample? Explain.

YOU MAY USE

THE SPACE

BELOW FOR SCRATCH

WORK,

BUT

ONLY

EQUATIONS

THA'I

ARE

WRITTEN

IN THE

ANSWER BOXES

PROVIDED

WILL

BE GRADED.

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College Board.

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rights reserved.

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Board on the

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11/12

AP@

CHEMISTRY

FREE-RESPONSE

OUESTIONS

Answer

Question

5

and

Question

6. The

Section II

score weighting

for

these

questions

is

l5

percent

each.

Your

responses

to these questions

will

be

graded

on the basis

of

the accuracy

and relevance

of the

information

cited.

Explanations

should

be clear

and

well

organized.

Examples

and

equations

may be included

in

your

responses where

appropriate.

Specific

answers

are

preferable

to

broad,

diffuse

responses.

Reaction

Equation

LHi,,s

ASfnt

AGint

X

C(s) +

HzO(s)

?

CO(s)

+ H2(s)

+131kJ

mol-r

+134

J

mol-l

K-l

+9i

kJ mol-r

Y

co2(s)

+H2(s)

?

Co(s)

+

H,o(s)

+41

kJ

mol-r

+42

J mol-l K-l

+

29

kJ

mol-l

Z

2

Co(s)

P

c(') +

Co2(s)

,I

,)

'l

Answer

the

following questions

using the

information

related to

reactions

X

,

Y,

and

Z

in

the table

above.

(a)

For reaction

X,

write

the

expression

for

the

equilibrium

constant,

K,,.

(b)

For

reaction

X, will

the

equilibrium

constant,

K'

increase.

decrease,

or remain

the same

if

the

temperature

rises

above

298

K ?

Justify

your

answer.

(c)

Forreaction

Y at298

K, is the value

of K,

Ereater

than

I,

less than

l, or equal

to

l? Justiiy

your

answer.

(d)

For

reaction

Y at 298

K,

which

is

larger:

the

total

bond energy

of

the

reactants

or the total

bond

energy of

the

products'/

Explain.

(e)

Is

the

following

starement true

or

false?

Justify your

answer.

"On

the

basis

of

the

data in

the table,

it can

be

predicted

that reaction

Y rvill

occur more

rlpidly than

reaction

X

will

occur."

(f)

Considerreaction

Z

at298K.

(i)

Is

A5"

for

the reaction positive,

negative,

or zero'/

Justify

your

answer.

(ii)

Determine

the

value

of A11o

for

the reaction.

(iii)

A

sealed glass

reaction

vessel contains

only

CO(g) and

a

small

amount

of

C(s).

If

a

:eaction

occurs

and

the temperature

is

held

constant

at298 K, rvill

the

pressure

in

the

reaction

vessel

increase,

decrease,

or remain

the same

over

time? Explain.

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AP Chem FRQ Practice 2009