2014 Tests and Keys.pdf

7/25/2019 2014 Tests and Keys.pdf

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CHM1311A Midterm #1A 2014 Page 1 of 10

LAST NAME: __________________________________________________________

FIRST NAME: _________________________________________________________

Student Number: ______________________________________________________

CHM 1311 A

Midterm 1 A

Fall 2014

P l e a s e k e e p y o u r w o r k c o v e r e d a t a l l t i m e s a n d k e e p y o u r e y e s o n y o u r

o w n p a p e r C h e a t i n g o r a n y a p p e a r a n c e o f c h e a t i n g w i l l r e s u l t i n a n F i n

t h e c o u r s e a n d p o s s i b l e e x p u l s i o n f r o m t h e u n i v e r s i t y .

There are 10 pages in this test. A periodic table and data sheets are

provided at the end. You may rip these pages off of the exam and use

them to cover your work during the test. Any scratch work should be

done on the back of these pages.

Please show all work to receive partial credit.

You have 80 minutes to complete the test.


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#1. (10 points) Short Answer Questions

a)

The standard heat of formation of solid ammonium chloride is 314.4 kJ. Write thechemical equation for the reaction to which this value applies (include phases).

b)

Name the following compounds:

Co(ClO)2 _________________________________________________

CaSO4 7 H2O _________________________________________________

c)

Complete the following table:

d)

Breaking chemical bonds is always an endothermic process. TRUE FALSE

e)

If the molar mass of a gas is doubled, the root-mean-squared speed of the molecules

will increase by a factor of ______________________.

f)

You take a 4.0 L volume of gas at 600 K. You expand the gas to an 8.0 L volume and

simultaneously heat the vessel to 1200 K. The pressure of the gas:DOUBLES HALVES QUADRUPLES STAYS CONSTANT

g)

Which compound has the highest oxidation state of nitrogen?

NO+ N2 NH3 NO2 N2O NO3

h)

When the power was turned off to a 125 L water heater, the temperature of the water

dropped from 75.0C to 22.5C. The amount of heat, in kilojoules, transferred to the

surroundings was: ___________________________________________________.

BONUS: The energy change shown in the diagram at right corresponds to a(n):

! EXOTHERMIC CONTRACTION

! ENDOTHERMIC CONTRACTION

! EXOTHERMIC EXPANSION

! ENDOTHERMIC EXPANSION

Element Mass NumberNumber of

protonsNumber ofelectrons

Number ofneutrons

Charge

Se

79 2

Energy

U1

U2

q W


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#2. 45.0 g of solid calcium carbonate is added to 1.25 L of an aqueous hydrochloric acidsolution. The hydrochloric acid solution has a density of 1.13 g/mL and is 25.7% acid bymass. The solid calcium carbonate reacts with the acid to yield liquid water, aqueouscalcium chloride, and carbon dioxide gas.

a)

(2 pts) Write a balanced chemical equation for the described reaction, including phases.

b)

(3 pts) What is the initial molarity of the acid solution?

Answer: __________________________________

c)

(5 pts) What is the molarity of the acid solution after the reaction is complete? You mayassume no volume changes.

Answer: __________________________________


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#3. A 3.902 g sample of an unknown compound containing only C, H, and O is combustedin an oxygen-rich environment.

a)

(3 pts) The CO2 gas produced in the reaction is collected over water at 20.00C in a5.000 L flask. The pressure in the flask is measured to be 100.52 kPa. What is thenumber of moles of carbon dioxide gas produced in the combustion?

Answer : __________________________________

b)

(5 pts) The reaction was found to also produce 3.633 g of liquid H2O. What is theempirical formula of the unknown compound?

Answer : __________________________________

c)

(2 pts) If the molecular mass of the unknown compound is found to be 116.2 u, what isits molecular formula?

Answer : __________________________________


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#4. This past summer, Dr. Fox went scuba diving in False Bay, South Africa, where thewater temperature was a chilly 13.5C. Despite wearing two 5 mm thick neoprene wetsuits,Dr. Fox still lost body heat at a rate of 38.0 J per second.

a)

(2 pts) How much body heat, in kJ, was lost over the course of a 45.0 min dive?

Answer : __________________________

b)

(3 pts) To recuperate this energy loss, Dr. Fox decides to eat a candy bar, which containsglucose, C6H12O6. Using the data tables, determine the enthalpy of combustion ofglucose, in kJ/mol.

Answer : __________________________

c)

(5 pts) If the candy bar contains 8.55% glucose by mass, how many grams of it will Dr.Fox need to eat to balance out the heat lost in part (a)?

Answer : __________________________


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#5. Cyanide ion, CN, is the conjugate base of a highly poisonous substance, hydrogencyanide (and if you saw the movie Skyfallyou saw its effects). In an environmental test forcyanide, the ion is treated in a redox reaction in basic solution with permanganate.

CN(aq) + MnO4(aq) CNO(aq) + MnO2(s) (basic conditions)

a)

(5 pts) Determine the overall balanced redox reaction equation.

b)

(5 pts) 450.0 mL of a 0.02270 M Ca(CN)2solution are added to 725.0 mL of a 0.01055 MKMnO4solution. If the above reaction has a percent yield of 78.3%, what is the expectedmass of solid manganese dioxide?

Answer: _____________________________


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CHM1311A Midterm #2A - 2014 Page 1 of 10

LAST NAME: __________________________________________________________

FIRST NAME: _________________________________________________________

Student Number: ______________________________________________________

CHM 1311 A

Midterm 2 A

Fall 2014

P l e a s e k e e p y o u r w o r k c o v e r e d a t a l l t i m e s a n d k e e p y o u r e y e s o n y o u r o w n

p a p e r C h e a t i n g o r a n y a p p e a r a n c e o f c h e a t i n g w i l l r e s u l t i n a n F i n t h e

c o u r s e a n d p o s s i b l e e x p u l s i o n f r o m t h e u n i v e r s i t y .

There are 10 pages in this test. A periodic table, data tables, and a formula

sheet are provided at the end. You may gently remove these pages off and

use them to cover your work. Any scratch work should be done on the back

of these pages.


You have 80 minutes to complete the test.


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1.

(10 pts) Short Answer Questions

a.

For the majority of reactions, reaction rate is fastest when:

Eahigh, T low Eahigh, T high Ealow, T low Ealow, T high

b.

Benzoic acid is titrated with sodium hydroxide. At the equivalence point, the pH will be:

ACIDIC NEUTRAL BASIC IMPOSSIBLE TO PREDICT

c.

The steady-state assumption states that intermediates are consumed at a constant rate.

TRUE FALSE

d.

For the reaction 2 A B + 3 C the value of K is 44.5 at 25C. The value of K for the

reaction 2 B + 6 C 4 A would be _________________________________.

e.

Predict the products of the following acid-base reaction. Is K > or < 1?

N3 + HF ______________________________________ K > 1 K < 1

f.

For a second order reaction, the plot of _______________________________ versus time will

yield a straight line, with a slope equal to _____________; its unit is ___________________.

g.

A chemical equilibrium can be considered to be going to completion when the value of

K is at least 1010

105

10 105

or greater.

h.

The conjugate acid and conjugate base of HPO42are ______________________________

and ___________________________ respectively.

BONUS:

Draw representative concentration lines/curves forboth A and B as a function of time in thefollowing first-order decomposition:

A 2 B

Dont forget to label your lines/curves!

Concentration

Time


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2.

Peroxyacetyl nitrate (PAN) is an air pollutant produced during photochemical smog events.PAN is unstable and dissociates into peroxyacetyl radicals and nitrogen dioxide.

a)

(3 pts) Using the data in the table below, derive a rate law for the decomposition of PAN at25.0C, as well as the value of the rate constant (with appropriate units).

TrialInitial [PAN]

(M)Initial Rate(M/min)

1 8.30x1010 1.92x1011

2 1.66x109 3.84x1011

3 2.49x109 5.78x1011

Rate law is: ___________________________

Rate constant is: ___________________________

b)

(2 pts) The decomposition of PAN has a half-life of 35.0 hr at 0.00C. What is the rateconstant for this reaction at this temperature? Use the same units as part (a).

c)

(3 pts) What is the activation energy, in kJ/mol, for this reaction?

d)

(2 pts) The enthalpy for the decomposition ofPAN is about 88 kJ/mol. On the axes provided,draw a representative reaction profile for thisreaction, with labels.

reaction coordinate

Energy

CH3COONO2 CH3COO + NO2

O O

PAN


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3.

Rick Grimes and his group of survivors are dealing with a major lack of resources in thezombie apocalypse. Their current water source is contaminated and needs to be treated withchlorine to be disinfected. Eugene suggests they produce the needed chlorine via the gas-phase electrolysis of salt:

2 NaCl (g) ! 2 Na(g) + Cl2(g)

a)

(6 pts) The above reaction is carried out at 750 K using 1.25 kg of salt in a 35.0 L reactionvessel. If only 0.120 kg of chlorine gas is obtained at equilibrium, what is the value of KCat this temperature?

Answer = ______________________

b)

(2 pts) What is the value of KPat 750 K?

Answer = ______________________

c)

(2 pts)The equilibrium mixture from part (a) is transferred to a 20.0 L container. What isthe qualitative effect on the value of KC? Explain, in one or two sentences.


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4.

You wish to determine the pH of a 0.0200 M solution of NH4NO2.

a)

(2 pts) The Kbof ammonia is 1.8x105. What is the Kavalue of its conjugate acid?

Answer = ______________________

b)

(6 pts) Determine the [H3O+] and [OH] produced by the hydrolysis (if any) of 0.0200 MNH4NO2.

[H3O+] = ______________________ [OH] = ______________________

c)

(2 pts) Calculate the expected pH of the solution.

Answer = ______________________


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5.

Your lab TA asks you to prepare a buffer solution with a pH of 7.40. The following reagentsare all available to you: 550 mL of 0.200 M formic acid, 450 mL of 0.200 M hypochlorousacid, solid sodium formate and solid sodium hypochlorite.

a)

(2 pts) Which 2 ingredients will you use to prepare the desired buffer?

b)

(2 pts) What is the base/acid ratio in the desired buffer?

Answer: ______________________c)

(3 pts) What mass (in g) of solid base must you dissolve in the corresponding acid solutionto achieve the desired buffer pH?

Answer: _____________________

d)

(3 pts) If 1.00 mL of 1.00 M NaOH is added to the buffer solution, what will be the new pH?

Answer: __________________________


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CHM1311A Final Exam 2014 Page 1 of 15

Surname (last name): __________________________________________________

Given name (First name): _____________________________________________

Student Number: ______________________________________________________

Seat Number: ___________

CHM 1311 A

Final Exam

December 2014

Attention: If you didnt have Dr. Focsaneanu (Fox) as your Instructor, you

shouldnt be writing this exam

P l e a s e k e e p y o u r w o r k c o v e r e d a t a l l t i m e s a n d k e e p y o u r e y e s o n y o u r

o w n p a p e r C h e a t i n g o r a n y a p p e a r a n c e o f c h e a t i n g w i l l r e s u l t i n a n F i n

t h e c o u r s e a n d p o s s i b l e e x p u l s i o n f r o m t h e u n i v e r s i t y .

There are 15 pages in this test. A periodic table, data tables, and a

formula sheet are provided at the end. You may rip these pages off of the

exam and use them to cover your work. Any scratch work should be done

on the back of these pages.


You have 180 minutes to complete the exam.


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1.

(20 points) Short Answer Questions.

a)

The number of atoms in 10.0 g of CaCO3(100.0 g/mol) is:

18.1 x 1022atoms 6.02 x 1022atoms

3.01 x 1023atoms 12.1 x 1023atoms

b)


c)

Balance the following reaction:

____ Fe (s) + ____ HCl (aq) ! ____ FeCl3(s) + ____ H2(g)

When 4.55 g of Fe (s) was reacted with HCl (aq), 0.101 g of H2 (g) was formed. The

percent yield of the reaction is _____________________.

d)

Which of the following isotopes has the greatest number of neutrons?

17

35Cl 19

40K

1737Cl 20

40Ca

e)

On the axes provided a right, draw a line (orcurve) representing the percent ionization ofa weak acid as a function of the initialconcentration of the acid.

f)

An exothermic expansion of a gas has a POSITIVE NEGATIVE value of W,

a POSITIVE NEGATIVE value of q, and a POSITIVE NEGATIVE

value of !U.

g)

In the following reaction, indicate the oxidizing agent:

NO (g) + O3(g) ! NO2(g) + O2 (g)

h)

Phosphorous acid has pKa1= 1.30 and pKa2= 6.70. An aqueous solution of this acid istitrated with NaOH (aq). At thefirstequivalence point, the pH of the solution will be

ACIDIC BASIC NEUTRAL

Write the equation for the expected hydrolysis:

100%

80%

60%

40%

20%

Initial Concentration of Acid

PercentIonization


15/43


i)

According to the Bohr Model, which of the following electronic transitions correspondsto the absorption of a photon with the shortest wavelength?

n = 1!n= 3 n = 2!n= 3 n = 3!n= 1 n = 3!n= 2

j)

Write a balanced net ionic equation for the expected reaction that occurs when 1.0 MMgCl2is mixed with 1.0 M AgNO3.

k)

It is possible to prepare a buffer by taking a weak acid and titrating it with a strong

acid to the half equivalence point. TRUE FALSE

l)

For a given reaction, the plot of lnk versus 1/T yields a slope of - 13.9 and a y-intercept

of 2.6x106

. Knowing this information, the reaction has:

Ea> 0 !H < 0 Ea< 0 !H > 0

m)

Determine the overall balanced redox reaction (acidic conditions) from the followinghalf reactions:

Al !Al2O3

Cu+! Cu

OVERALL: ___________________________________________________________________

n)

A solution contains 0.050 M Pb2+. The minimum chloride concentration needed to

observe the formation of a solid precipitate is: ___________________________________

o)

Name two ways to accelerate a chemical reaction:

i.

___________________________________________________________

ii.

___________________________________________________________

BONUS

How many nodal planes are there in thef orbitals? _____________

Draw the Lewis structure of CO2.


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2.

Barium sulfate is used in medical imaging of the gastrointestinal tract because it isopaque to X rays. A barium sulfate solution is ingested by the patient, whose stomachand intestines can then be visualized via X-ray imaging.

a)

(5 pts) If a patient ingests 200 mL of a saturated barium sulfate solution, how manytoxic Ba2+ions has the patient consumed?

Answer: ______________________________

b)

(3 pts) There are some data that suggest that zinc lozenges can significantly shorten theduration of a cold. If the solubility of zinc acetate, Zn(CH3COO)2, is 43.0 g/L, what is

the Kspof this compound?

c)

(2 pts) How might one improve the solubility of zinc acetate? Explain, using LeChateliers Principle.


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3.

The mechanism for the gas-phase reaction described by the equation

A + B ! Cis suggested to be:

A! X

X + B! C

a)

(4 pts) Assuming that [X] is governed by steady-state conditions, derive the rate law forthe production of C in terms of [A] and [B], and any appropriate k values.

b)

(1 pt) What is the expected overall order of the rate law at verylowgas pressures?

ZERO ORDER FIRST ORDER SECOND ORDER THIRD ORDER

c)

(1 pt) What is the expected overall order of the rate law at very highgas pressures?


d)

(4 pts) Using the graph below, calculate the initial rate andaverage rate (both in M/s)for the reaction.

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30 35 40

Conc

entration(mol/L)

Time (min)


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4.

Quantum Numbers and Electronic Configurations.

a)

(3 pts) For the following sets of quantum numbers, give the subshell label, the allowedvalues of mland the number of orbitals in the subshell (the first row is an example).

nand l subshell label mlvalues number of orbitals

n = 0 and l= 0 1s 0 1

n = 5 and l= 1

n= 3 and l= 2

b)

(3 pts) How many electrons can be described by each of the following sets of quantumnumbers?

i. n= 4, l= 2, ml= 1

ii.

n= 3, l= 3, ml= -1, ms= !

iii. n= 4, l= 3

c)

(4 pts) Draw the orbital energy diagram for Fe3+in the space below. What is theexpected magnetism of this species?


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5.

The haemoglobin content of blood is about 15.5g/100mL. The molar mass ofhaemoglobin is about 64 500 g/mol, and there are four iron atoms in each haemoglobinmolecule.

a)

(5 pts) Approximately how many iron atoms are present in the 6 L of blood in a typicaladult?

Answer: _________________________

b)

(5 pts) One isotope of iron, iron-58, has a relative abundance of 0.280% and an exactmass of 57.933 g/mol. Approximately how many litres of human blood would contain

1.00 g of iron-58?

Answer: ___________________________


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6.

A calorimeter contains 24.0 mL of water at 13.0C. When 2.20 g of X (molar mass 47.0

g/mol) is added, it dissolves via the reaction: X(s) ! X(aq)

and the temperature of the solution increases to 28.0C.

a)

(4 pts) Calculate the enthalpy change for the dissolution, in kJ/mol. You may assumethe specific heat capacity and density of the solution are equal to those of pure water;

however, you may NOT assume that the mass of the solution is equal to the mass of thewater.

Answer: _____________________________

b)

(2 pts) Calculate the internal energy change for the dissolution, in kJ/mol.

Answer: _____________________________

c)

(4 pts) Determine the enthalpy change for the following reaction, using the provided

data. X (s) ! 2Y (s) !H = ?

Y(s) ! Y(aq) !H = +24.7 kJ

2 Y(aq) ! X(aq) !H = -1.44 kJ

Answer: _____________________________


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7.

When Dr. Fox goes scuba diving, she uses NITROX, a special blend of enriched air thatallows for more repetitive dives by reducing the build-up of nitrogen in the blood (thatway, she wont get the bends!). The local scuba shop prepares 6.50 L tanks ofNITROX by mixing 26.0 g of O2with 44.2 g of N2at a temperature of 25.0C.

a)

(4 pts) What is the mole fraction of each gas in the mixture?

!of N2= _________________ !of O2= __________________

b)

(4 pts) What is the partial pressure of each gas, in bar?

Pof N2= _________________ Pof O2= __________________

c)

(2 pts) What will be the total pressure left in the tank after Dr. Fox breathes 85% of it byvolume during a dive?

PT= _________________________


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8.

(10 pts) You are performing atitration of 80.0 mL of 0.150 MHOCl with 0.150 M NaOH.Determine the pH of thesolution:

a)

(3 pts) initially

b)

(2 pts) at the half-equivalencepoint

c)

(4 pts) at the equivalence pointd)

(1 pt) Use these values tosketch a titration curve on thegraph provided.

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 1

pH

mL OH

added


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9.

45.0 g of solid calcium carbonate is added to 1.25 L of an aqueous hydrochloric acidsolution. The hydrochloric acid solution has a density of 1.13 g/mL and is 25.7% acid bymass. The solid calcium carbonate reacts with the acid to yield liquid water, aqueouscalcium chloride, and carbon dioxide gas.

a)


b)


Answer: __________________________________

c)


Answer: _____________________________


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#1. (10 points) Short Answer Questions

a)

The standard heat of formation of solid ammonium chloride is 314.4 kJ. Write thechemical equation for the reaction to which this value applies (include phases).

b)

Name the following compounds:

Co(ClO)2 _____cobalt (II) hypochlorite__________________

CaSO4 7 H2O _____calcium sulphate heptahydrate__________________

c)

Complete the following table:

d)


e)

If the molar mass of a gas is doubled, the root-mean-squared speed of the molecules

will increase by a factor of _____!__________.

f)

You take a 4.0 L volume of gas at 600 K. You expand the gas to an 8.0 L volume andsimultaneously heat the vessel to 1200 K. The pressure of the gas:

DOUBLES HALVES QUADRUPLES STAYS CONSTANT

g)

Which compound has the highest oxidation state of nitrogen?

NO+ N2 NH3 NO2 N2O NO3

h)

When the power was turned off to a 125 L water heater, the temperature of the water

dropped from 75.0C to 22.5C. The amount of heat, in kilojoules, transferred to the

surroundings was: _______2.75 x 104kJ (note that the sign isnt necessary in this case,

since it says transferred to._______.

BONUS: The energy change shown in the diagram at right corresponds to a(n):

! EXOTHERMIC CONTRACTION

! ENDOTHERMIC CONTRACTION

! EXOTHERMIC EXPANSION

! ENDOTHERMIC EXPANSION

Element Mass NumberNumber of

protonsNumber ofelectrons

Number ofneutrons

Charge

Se 79 34 36 45 2

!N2(g) + 2 H2(g) +!Cl2(g)!NH4Cl(s)

Energy

U1

U2

q W


25/43


#2. 45.0 g of solid calcium carbonate is added to 1.25 L of an aqueous hydrochloric acidsolution. The hydrochloric acid solution has a density of 1.13 g/mL and is 25.7% acid bymass. The solid calcium carbonate reacts with the acid to yield liquid water, aqueouscalcium chloride, and carbon dioxide gas.

This question is Petrucci Ch. 4 #110 and was covered in DGD #3

a)


CaCO3(s) + 2 HCl (aq) H2O (l) + CaCl2 (aq) + CO2(g)

b)


? mol HCl

L=

25.7 g HCl

100 g soln !1.13 g soln

mL soln !1000 mL

L !mol HCl

36.45 g HCl

=7.97 mol/L

Answer: ________7.97 M______________

c)


The question implies that there is excess HCl (i.e. CaCO3is the limiting reagent).

? initial mol HCl =1.25 L soln!7.97 mol HCl

L

=9.96 mol

? mol HCl reacted =45.0 g CaCO3 !mol CaCO3

100.1 g CaCO3!

2 mol HCl

1 mol CaCO3

=0.899 mol

? mol HCl leftover =9.96 mol 0.899 mol

=9.06 mol

? mol HCl leftover

L=

9.06 mol

1.25 L

=7.25 mol/L

Answer: ________7.25 M_________________


26/43


#3. A 3.902 g sample of an unknown compound containing only C, H, and O is combustedin an oxygen-rich environment.

This is a slightly changed version of the Sample Midterm Problem on Sapling

a)

(3 pts) The CO2 gas produced in the reaction is collected over water at 20.00C in a5.000 L flask. The pressure in the flask is measured to be 100.52 kPa. What is thenumber of moles of carbon dioxide gas produced in the combustion?

PH2O = 2.3393 kPa (fromTableondatasheets)

Ptotal = PCO2 +PH2O

PCO2 = Ptotal !PH2O =100.52kPa-2.3393kPa= 98.18kPa

? mol CO2 =PCO2V

RT =

(98.18 kPa)(5.000 L)

(8.3145 kPa "L/mol "K)(293.15 K)= 0.2014 mol

Answer : _______0.2014 mol_______________

b)

(5 pts) The reaction was found to also produce 3.633 g of liquid H2O. What is theempirical formula of the unknown compound?

? mol C =0.2014 mol CO2 !1 mol C

1 mol CO2=0.2014 mol C

? mol H =3.633 g H2O!mol H2O

18.02 g H2O!

2 mol H

1 mol H2O= 0.4032 mol H

? g C= 0.2014 mol C!12.011 g C

1 mol C=2.42 g C

? g H= 0.4031 mol H!1.008 g H

1 mol H= 0.406 g H

"? g O=3.902 g sample 2.42 g C 0.406 g H =1.07 g O

? mol O =1.07 g O!1 mol O

15.999 g O=0.0669 mol O

"C0.20140.0669

H0.40320.0669

O0.06690.0669

=C3H6O

Answer : ________C3H6O_______________

c)

(2 pts) If the molecular mass of the unknown compound is found to be 116.2 u, what isits molecular formula?

MF mass

EF mass=

116 u

58 u=2

!MF =2"EF =C6H

12O

2

Answer : ______C6H12O2__________


27/43


#4. This past summer, Dr. Fox went scuba diving in False Bay, South Africa, where thewater temperature was a chilly 13.5C. Despite wearing two 5 mm thick neoprene wetsuits,Dr. Fox still lost body heat at a rate of 38.0 J per second.

NEW QUESTION: I actually thought up this question during the dive!

a)

(2 pts) How much body heat, in kJ, was lost over the course of a 45.0 min dive?

? kJ =45.0 min!60 s

1 min!

38.0 J

s!

1 kJ

1000 J=102.6 kJ

Technically, the sign here would be negative (to show heat leaving the system), but sincethis is already acknowledged in the question, its not necessary.

Answer : ____102.6 kJ____________

b)

(3 pts) To recuperate this energy loss, Dr. Fox decides to eat a candy bar, which containsglucose, C6H12O6. Using the data tables, determine the enthalpy of combustion ofglucose, in kJ/mol.

C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O (l)

!Hcomb = {(6 x !HfCO2) + (6 x !HfH2O)} {(1 x !HfC6H12O6) + (6 x !HfO2)}= {(6 x 393.5) + (6 x 285.8)} {(1 x 1273.3) + (6 x 0)}= 2802.5 kJ/mol

Answer : ______2802.5 kJ/mol___________c)

(5 pts) If the candy bar contains 8.55% glucose by mass, how many grams of it will Dr.Fox need to eat to balance out the heat lost in part (a)?

? g candy =102.6 kJ!mol C6H12O6

2802.5 kJ!

180 g C6H12O6mol C6H12O6

!

100 g candy

8.55 g C6H12O6

=77.1 g candy

Answer : ______77.1 g__________


28/43


#5. Cyanide ion, CN, is the conjugate base of a highly poisonous substance, hydrogencyanide (and if you saw the movie Skyfallyou saw its effects). In an environmental test forcyanide, the ion is treated in a redox reaction in basic solution with permanganate.

CN(aq) + MnO4(aq) CNO(aq) + MnO2(s) (basic conditions)

a)

(5 pts) Determine the overall balanced redox reaction equation.

This is taken directly from the course notes

oxidation: reduction:

CN CNO MnO4 MnO2

H2O + CN CNO MnO4 MnO2 + 2 H2O

H2O + CN CNO+ 2 H+ 4 H+ + MnO4 MnO2 + 2 H2O

2 OH+ H2O + CN CNO+ 2 H++ 2 OH 4 OH + 4 H++ MnO4 MnO2+ 2 H2O + 4 OH

2 OH + H2O + CN CNO+ 2 H2O 4 H2O + MnO4 MnO2 + 2 H2O + 4 OH

2 OH + CN CNO+ H2O 2 H2O + MnO4 MnO2 + 4 OH

2 OH + CN CNO+ H2O + 2 e 3 e+ 2 H2O + MnO4 MnO2 + 4 OH

6 OH + 3 CN 3 CNO+ 3 H2O + 6 e 6 e+ 4 H2O + 2 MnO4 2 MnO2 + 8 OH

Adding the two together and simplifying gives the overall balanced redox reaction:

H2O + 2 MnO4 + 3 CN 3 CNO+ 2 MnO2 + 2 OH

b)

(5 pts) 450.0 mL of a 0.02270 M Ca(CN)2solution are added to 725.0 mL of a 0.01055 MKMnO4solution. If the above reaction has a percent yield of 78.3%, what is the expected

mass of solid manganese dioxide?

? mol MnO2 from CN=0.4500 L !

0.02270 mol Ca(CN)2L

!

2 mol CN

1 mol Ca(CN)2!

2 mol MnO23 mol CN

=0.01362 mol

? mol MnO2 from MnO4=0.7250 L !

0.01055 mol KMnO4

L !

1 mol MnO4

1 mol KMnO4

!

2 mol MnO22 mol MnO

4

=0.007649 mol

Therefore, permanganate is the limiting reagent.

? actual g MnO2 = 0.007649 mol MnO2!86.94 g MnO2

mol MnO2

"

#$

%

&'!78.3%

= 0.52 g

Answer: _______0.52 g___________


29/43


1.

(10 pts) Short Answer Questions

a.

For the majority of reactions, reaction rate is fastest when: Using k = AeEa/RT

Eahigh, T low Eahigh, T high Ealow, T low Ealow, T high

b.

Benzoic acid is titrated with sodium hydroxide. At the equivalence point, the pH will be:

ACIDIC NEUTRAL BASIC IMPOSSIBLE TO PREDICT

c.

The steady-state assumption states that intermediates are consumed at a constant rate.

TRUE FALSE

d.

For the reaction 2 A B + 3 C the value of K is 44.5 at 25C. The value of K for the

reaction 2 B + 6 C 4 A would be ____K = 1/K2= 5.05x104_________________.

e.

Predict the products of the following acid-base reaction. Is K > or < 1?

N3 + HF __HN3 + F______________ K > 1 K < 1

f.

For a second order reaction, the plot of _____1/concentration___________ versus time will

yield a straight line, with a slope equal to ____k______; its unit is ____M1s1_______.

g.

A chemical equilibrium can be considered to be going to completion when the value of

K is at least 1010 105 10 105 or greater.

h.

The conjugate acid and conjugate base of HPO42are ______ H2PO4___________ and

_______ PO43 ________ respectively.

BONUS:

Draw representative concentration lines/curvesfor both A and B as a function of time in thefollowing first-orderdecomposition:

A 2 B

Dont forget to label your lines/curves!

At the EQ PT: benzoate ion hydrolyzes: C6H5COO + H2O C6H5COOH + OH

It states that intermediates are PRODUCED and CONSUMED at EQUAL RATES.

Ka= 6.6 x 104

Ka= 1.9 x 105

Concentra

tion

Time

[A]

[B]

Note: 2 moles of B formed forevery mol of A consumed!


30/43


2.

Peroxyacetyl nitrate (PAN) is an air pollutant produced during photochemical smog events.PAN is unstable and dissociates into peroxyacetyl radicals and nitrogen dioxide.

NOTE: THIS IS TAKEN FROM MIDTERM 2 2012

a)

(3 pts) Using the data in the table below, derive a rate law for the decomposition of PAN at25.0C, as well as the value of the rate constant (with appropriate units).

TrialInitial [PAN]

(M)Initial Rate(M/min)

1 8.30x1010 1.92x1011

2 1.66x109 3.84x1011

3 2.49x109 5.78x1011

k = rate[PAN]

= 1.92!1011

M "min1

8.30!1010

M =2.31!102 min1

Rate law is: ___rate = k[PAN]___________

Rate constant is: ___k = 0.0231 min1_________

b)

(2 pts) The decomposition of PAN has a half-life of 35.0 hr at 0.00C. What is the rateconstant for this reaction at this temperature? Use the same units as part (a).

Its first order, so:t12

=ln2

k!k =

ln2

t12

=ln2

35.0hr

1hr

60min= 3.30"10

4min

1

c)

(3 pts) What is the activation energy, in kJ/mol, for this reaction?

k1= 2.31x102min1@ T1= 298 Kk2= 3.30x104min1@ T2= 273 K

ln k

2

k1

!

"#

$

%&='

Ea

R

1

T2

' 1

T1

!

"#

$

%& ( ln

3.30)104min1

2.31)102min1!

"#

$

%&='

Ea

8.3145J *mol1K11

273K' 1

298K

!

"#

$

%&

Solve for Ea:Ea= 1.15x105J/mol = 115 kJ/mol

d)

(2 pts) The enthalpy for the decompositionof PAN is about 88 kJ/mol. On the axesprovided, draw a representative reactionprofile for this reaction, with labels.

CH3COONO2 CH3COO + NO2

O O

PAN

Trials 1 & 2: [PAN] x 2 rate x 2Or: Trials 1 & 3: [PAN] x 3 rate x 3

rate = k[PAN] (its first orde

reaction coordinate

Energy

Ea= 115 kJ/mol

!H = 88 kJ/mo

PAN (rxt)

products


31/43


3.

Rick Grimes and his group of survivors are dealing with a major lack of resources in thezombie apocalypse. Their current water source is contaminated and needs to be treated withchlorine to be disinfected. Eugene suggests they produce the needed chlorine via the gas-phase electrolysis of salt:

2 NaCl (g) ! 2 Na(g) + Cl2(g)

a)

(6 pts) The above reaction is carried out at 750 K using 1.25 kg of salt in a 35.0 L reactionvessel. If only 0.120 kg of chlorine gas is obtained at equilibrium, what is the value of KCat this temperature?

THIS IS JUST A TYPE 1 EQUILIBRIUM PROBLEM

? initial mol NaCl

L=1.25 kg!

1000 g

1 kg!

mol NaCl

58.44 g NaCl!

1

35.0 L= 0.6111 mol/L NaCl initial

? EQM mol Cl2L

=0.120 kg!1000 g

1 kg!

mol Cl270.90 g Cl2

!

1

35.0 L= 0.0484 mol/L Cl2 @ EQM

2 NaCl (g) ! 2 Na(g) + Cl2(g)

I 0.6111 0 0

C -2x +2x +x

-2(0.0484) +2(0.0484) +0.0484

E 0.5143 0.0968 0.0484

KC =[Na]2[Cl2 ]

[NaCl]2 =

(0.0968)2(0.0484)

(0.5143)2 =1.71x103

Answer = ______________________

b)

(2 pts) What is the value of KPat 750 K?

KP =KC(RT)!ngas

= (1.71x103)(0.083145!750)32 = 0.107

Answer = _____0.107_____

c)

(2 pts)The equilibrium mixture from part (a) is transferred to a 20.0 L container. What isthe qualitative effect on the value of KC? Explain, in one or two sentences.

The volume of the new container is SMALLER than the volume of the original container. Thismeans that the equilibrium will shift to the side that contains FEWER gas particles (toaccommodate the decrease in available space). In this case, the equilibrium will shift to theLEFT and so K will DECREASE.


32/43


4.

You wish to determine the pH of a 0.0200 M solution of NH4NO2.

THIS QUESTION WAS COVERED IN DGD#9

a)

(2 pts) The Kbof ammonia is 1.8x105. What is the Kavalue of its conjugate acid?

Ka =K

W

Kb

=

1.0x1014

1.8x105

=5.56x1010

Answer = ______________________

b)

(6 pts) Determine the [H3O+] and [OH] produced by the hydrolysis (if any) of 0.0200 MNH4NO2.

Both ions will hydrolyze, so two ICE tables are necessary:

NH4+ + H2O ! H3O+ + NH3

I 0.0200 - 0 0C -x - +x +xE 0.0200 -x - x x

NO2 + H2O ! OH + HNO2

I 0.0200 - 0 0C -x - +x +x

E 0.0200 -x - x x

[H3O+] = ____3.33x106M_______ [OH] = ___5.27x107M______

c)

(2 pts) Calculate the expected pH of the solution.

[H3O+] > [OH], therefore, the excess H3O+will determine the pH of the solution:

leftover [H3O+] = 3.33x106 5.27x107= 2.80x106M

pH = log(2.80x106) = 5.55

Answer = _____5.55_________


33/43


5.

Your lab TA asks you to prepare a buffer solution with a pH of 7.40. The following reagentsare all available to you: 550 mL of 0.200 M formic acid, 450 mL of 0.200 M hypochlorousacid, solid sodium formate and solid sodium hypochlorite.

THIS IS A SLIGHTLY MODIFIED VERSION OF THE EXAMPLES IN THE COURSE NOTES

a)

(2 pts) Which 2 ingredients will you use to prepare the desired buffer?

HCOOH/HCOO pKa= log(1.8x104) = 3.74HOCl/OCl pKa= log(2.9x108) = 7.54Therefore, hypochlorous acid/sodium hypochlorite is the appropriate choice.

b)

(2 pts) What is the base/acid ratio in the desired buffer?

pH= pKa + log [OCl]

[HOCl]

!

"#

$

%&

' [OCl

][HOCl]

=10pHpKa =107.40-7.54 = 0.724

Answer: _____0.724________

c)

(3 pts) What mass (in g) of solid base must you dissolve in the corresponding acid solutionto achieve the desired buffer pH?

[OCl]

[HOCl]= 0.724

![OCl]= 0.724"[HOCl]=0.724"0.200 M =0.145 M

? g NaOCl =0.450 L" 0.145 mol OCl

L "

1 mol NaOCl1 mol OCl

"74.44 g NaOCl

mol NaOCl=4.86 g

Answer: _____4.86 g_______

d)

(3 pts) If 1.00 mL of 1.00 M NaOH is added to the buffer solution, what will be the new pH?

? mol OH

added =0.00100 L!1.00 mol OH

L=0.00100 mol

? mol OCl

initial = 0.450 L!0.145 mol OCl

L=0.06525 mol

? mol HOCl initial =0.450 L!0.200 mol HOCl

L= 0.0900 mol

pH = pKa + log [OCl]

[HOCl]

!

"#

$

%&=7.54+ log

0.06625

0.0890

!

"#

$

%&=7.41

Answer: __________7.41_______

HOCl + OH!

OCl + H2OB 0.0900 0.06525 -

A 0.001 -

M -0.001 -0.001 +0.001 -A 0.0890 0 0.06625 -


34/43


1.

(20 points) Short Answer Questions.

a)

The number of atoms in 10.0 g of CaCO3(100.0 g/mol) is:

18.1 x 1022atoms 6.02 x 1022atoms

3.01 x 1023atoms 12.1 x 1023atoms

b)


c)

Balance the following reaction:

__2__ Fe (s) + __6__ HCl (aq) ! __2__ FeCl3(s) + __3__ H2(g)

When 4.55 g of Fe (s) was reacted with HCl (aq), 0.101 g of H2 (g) was formed. The

percent yield of the reaction is ___41%_________.

d)

Which of the following isotopes has the greatest number of neutrons?

17

35Cl 19

40K

1737Cl 20

40Ca

e)

On the axes provided a right, draw a line (orcurve) representing the percent ionization ofa weak acid as a function of the initialconcentration of the acid.

f)

An exothermic expansion of a gas has a POSITIVE NEGATIVE value of W,

a POSITIVE NEGATIVE value of q, and a POSITIVE NEGATIVE

value of !U.

g)

In the following reaction, indicate the oxidizing agent:

NO (g) + O3(g) ! NO2(g) + O2 (g)

h)

Phosphorous acid has pKa1= 1.30 and pKa2= 6.70. An aqueous solution of this acid istitrated with NaOH (aq). At thefirstequivalence point, the pH of the solution will be

ACIDIC BASIC NEUTRAL

Write the equation for the expected hydrolysis:

100%

80%

60%

40%

20%

Initial Concentration of Acid

PercentIonization

H2PO3(aq) + H2O(l) ! HPO32(aq) + H3O+(l)


35/43


i)

According to the Bohr Model, which of the following electronic transitions correspondsto the absorption of a photon with the shortest wavelength?

n = 1!n= 3 n = 2!n= 3 n = 3!n= 1 n = 3!n= 2

j)

Write a balanced net ionic equation for the expected reaction that occurs when 1.0 MMgCl2is mixed with 1.0 M AgNO3.

k)

It is possible to prepare a buffer by taking a weak acid and titrating it with a strong

acid to the half equivalence point. TRUE FALSE

l)

For a given reaction, the plot of lnk versus 1/T yields a slope of - 13.9 and a y-intercept

of 2.6x106

. Knowing this information, the reaction has:

Ea> 0 !H < 0 Ea< 0 !H > 0

m)

Determine the overall balanced redox reaction (acidic conditions) from the followinghalf reactions:

3 H2O + 2 Al !Al2O3 + 6 H+ + 6 e

6 e +6 Cu+! 6 Cu

OVERALL: ________3 H2O + 2 Al + 6 Cu+!Al2O3 + 6 H+ + 6 Cu________________

n)

A solution contains 0.050 M Pb2+. The minimum chloride concentration needed to

observe the formation of a solid precipitate is: __[Cl] = "(Ksp/[Pb2+]) = 0.019 M________

o)

Name two ways to accelerate a chemical reaction:

i.

___add catalyst, increase concentrations, increase temperature, etc..._______

ii.

___________________________________________________________

BONUS

How many nodal planes are there in thef orbitals? _____3________

Draw the Lewis structure of CO2.

Ag+ (aq) + Cl(aq) ! AgCl (s)


36/43


2.

Barium sulfate is used in medical imaging of the gastrointestinal tract because it isopaque to X rays. A barium sulfate solution is ingested by the patient, whose stomachand intestines can then be visualized via X-ray imaging.

a)

(5 pts) If a patient ingests 200 mL of a saturated barium sulfate solution, how manytoxic Ba2+ions has the patient consumed?

Kspof BaSO4= 1.1 x 10-10

Let s represent the solubility of barium sulfate:BaSO4(s) ! Ba2+(aq) + SO42(aq)

I m 0 0

C s +s +sE m s s s

Ksp= [Ba2+][SO42] = s2

s = !Ksp= !(1.1x1010) = 1.05x105M = [Ba2+]

? Ba2+

ions = 200 mL!1 L

1000 mL!

1.05x105

mol Ba2+

L!

6.022x1023

Ba2+

ions

mol Ba2+

ions

=1.3x1018

ions

Answer: ______________________________

b)

(3 pts) There are some data that suggest that zinc lozenges can significantly shorten theduration of a cold. If the solubility of zinc acetate, Zn(CH3COO)2, is 43.0 g/L, what isthe Kspof this compound?

Let s represent the solubility of zinc acetate:

s =

? mol Zn(CH3COO)2L

=

43.0 g Zn(CH3COO)2

1 L !

mol Zn(CH3COO)2183.5 g Zn(CH3COO)2

=0.234 mol/L

Zn(CH3COO)2(s) ! Zn2+(aq) + 2 CH3COO(aq)

I m 0 0

C s +s +2s

E m s s 2s

Ksp= [Zn2+][CH3COO]2= (s)(2s)2= 4s3= 4 x (0.234)3= 0.051

c)

(2 pts) How might one improve the solubility of zinc acetate? Explain, using LeChateliers Principle.

The anion formed in the dissolution, acetate, is the CONJUGATE BASE of a WEAK ACID.Therefore, it will HYDROLYZE when added to water:

CH3COO + H2O ! CH3COOH + OHThus, this salt will be MORE SOLUBLE in ACIDIC SOLUTIONS (because the acid willconsume the produced OHand pull the equilibrium forward).


37/43


3.

The mechanism for the gas-phase reaction described by the equation

A + B ! Cis suggested to be:

A! X

X + B! C

a)

(4 pts) Assuming that [X] is governed by steady-state conditions, derive the rate law forthe production of C in terms of [A] and [B], and any appropriate k values.

rate = k2[X][B]

SSA for X: rates of reactions that form X = rates of reactions that consume Xrate forward = rate reverse + rate

k1[A]= k

1[X]+ k

2[X][B]

![X]=k1[A]

k1+ k

2[B]

rate = k2

k1[A]

k1+ k

2[B]

"

#$

%

&'[B]

=k1k2[A][B]

k1+ k

2[B]

b)

(1 pt) What is the expected overall order of the rate law at verylowgas pressures?


c)

(1 pt) What is the expected overall order of the rate law at very highgas pressures?


d)

(4 pts) Using the graph below, calculate the initial rate andaverage rate (both in M/s)for the reaction.

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30 35 40

Concentration(mol/L)

Time (min)

Initial Rate = slope of tangent

Average Rate = slope of diagonal


38/43


4.

Quantum Numbers and Electronic Configurations.

a)

(3 pts) For the following sets of quantum numbers, give the subshell label, the allowedvalues of mland the number of orbitals in the subshell (the first row is an example).

nand l subshell label mlvalues number of orbitals

n = 0 and l= 0 1s 0 1

n = 5 and l= 1 5p 1, 0, +1 3

n= 3 and l= 2 3d 2, 1, 0, +1, +2 5

b)

(3 pts) How many electrons can be described by each of the following sets of quantumnumbers?

i. n= 4, l= 2, ml= 1 This is one of the five possible 4d orbitals. It can hold 2

electrons.

ii.

n= 3, l= 3, ml= -1, ms= ! This is an impossible set of quantum numbers.Therefore NO electrons can have this set.

iii. n= 4, l= 3 This is the 4f subshell. There are 7 orbitals in this subshell, and

each can hold 2 electrons. Therefore, 14 electrons total.

c)

(4 pts) Draw the orbital energy diagram for Fe3+in the space below. What is theexpected magnetism of this species?

Fe (neutral atom) = 1s22s22p63s23p64s23d6Fe3+(ion) = 1s22s22p63s23p64s03d5Since this ion has unpaired electrons, it is PARAMAGNETIC.

!"#$%&

()

*)

+)

*,

+,

+-

.)


39/43


5.

The haemoglobin content of blood is about 15.5g/100mL. The molar mass ofhaemoglobin is about 64 500 g/mol, and there are four iron atoms in each haemoglobinmolecule.

a)

(5 pts) Approximately how many iron atoms are present in the 6 L of blood in a typicaladult?

Let Hb = haemoglobin

? Fe atoms =6 L blood!1000 mL

1 L!

15.5 g Hb

100 mL blood!

mol Hb

64 500 g Hb!

4 mol Fe

1 mol Hb!

6.022x1023 Fe atom

mol Fe

=3.5x1022 atoms

Answer: _________________________

b)

(5 pts) One isotope of iron, iron-58, has a relative abundance of 0.280% and an exactmass of 57.933 g/mol. Approximately how many litres of human blood would contain1.00 g of iron-58?

? L blood =1.00 g 58Fe! mol

58

Fe57.933 g 58Fe

! 100 mol Fe0.280 mol 58Fe

!1 mol Hb4 mol Fe

! 64500 g Hbmol Hb

!100 mL blood15.5 g Hb

=6.4x103 mL!1 L blood

1000 mL blood

=641 L

Answer: ___________________________


40/43


6.

A calorimeter contains 24.0 mL of water at 13.0C. When 2.20 g of X (molar mass 47.0

g/mol) is added, it dissolves via the reaction: X(s) ! X(aq)

and the temperature of the solution increases to 28.0C.

a)

(4 pts) Calculate the enthalpy change for the dissolution, in kJ/mol. You may assumethe specific heat capacity and density of the solution are equal to those of pure water;

however, you may NOT assume that the mass of the solution is equal to the mass of thewater.

qsoln

= msoln

csoln!T

soln

= (2.20g + 24.0g)(4.184J

gC)(28.0C 13.0C)

= + 1644 J

!qrxn

= 1644 J

!Hrxn

=

? kJmol

=

1644 J2.20 g

"47.0 gmol

"1 kJ

1000 J =35.1 kJ/mol

Answer: _____________________________

b)

(2 pts) Calculate the internal energy change for the dissolution, in kJ/mol.

!U = q + W = !H + WBut: there are no gases involved. Therefore W ~ 0 and thus:

!U ~ !H = 35.1 kJ/mol

Answer: _____________________________

c)

(4 pts) Determine the enthalpy change for the following reaction, using the provided

data. X (s) ! 2Y (s) !H = ?

Y(s) ! Y(aq) !H = +24.7 kJ

2 Y(aq) ! X(aq) !H = -1.44 kJ

Using the value from part (a):

(same)X(s) X(aq)

!H = 35.1 kJ

3 reversed X(aq) 2 Y(aq) !H = +1.44 kJ

reversed, x2 2 Y(aq) 2 Y(s) !H = -49.4 kJ

SUM X (s) 2Y (s) !H = 83.2 kJ

Answer: _____________________________


41/43


7.

When Dr. Fox goes scuba diving, she uses NITROX, a special blend of enriched air thatallows for more repetitive dives by reducing the build-up of nitrogen in the blood (thatway, she wont get the bends!). The local scuba shop prepares 6.50 L tanks ofNITROX by mixing 26.0 g of O2with 44.2 g of N2at a temperature of 25.0C.

a)

(4 pts) What is the mole fraction of each gas in the mixture?

? mol O2= 26.0 g O

2!

mol O2

31.998 g O2

= 0.812 mol O2

? mol N2= 44.2 g N

2!

mol N2

28.014g N2

= 1.578 mol N2

Total mol nT= 0.812 + 1.578 = 2.39 mol

"!N

2

=1.578 mol

2.39 mol = 0.660

"!O

2

=0.812 mol

2.39 mol= 0.340

!of N2= _________________ !of O2= __________________

b)

(4 pts) What is the partial pressure of each gas, in bar?

PT =nTRT

V=

(2.39 mol)(0.083145 L !bar/mol !K)(298K)

6.50 L

= 9.11 bar

PN2 = !N2 " PT = (0.660)(9.11 atm)

= 6.0 bar

PO2

= !O2

" PT = (0.340)(9.11 atm)

= 3.1 bar

Pof N2= _________________ Pof O2= __________________

c)

(2 pts) What will be the total pressure left in the tank after Dr. Fox breathes 85% of it byvolume during a dive?

If 85% has been consumed, there is 15% left.V2is 15% of V1 Therefore, P2is 15% of P1P2= (0.15)(9.11 bar) = 1.4 bar

PT= _________________________


42/43


8.

(10 pts) You are performing atitration of 80.0 mL of 0.150 MHOCl with 0.150 M NaOH.Determine the pH of thesolution:

a)

(3 pts) initially

b)

(2 pts) at the half-equivalencepoint

c)

(4 pts) at the equivalence pointd)

(1 pt) Use these values tosketch a titration curve on thegraph provided.

a) initial pH:

HOCl + H2O ! H3O+ + OClI 0.150 - 0 0

C x - +x +xE 0.150 x - x x

pH = log(6.60x105) = 4.18

b) At the!equivalence point: pH = pKa= log(2.9x108) = 7.54

c) At the equivalence point:

mol HOCl = mol OHadded = 0.0120 mol (this corresponds to adding 80.0 mL of base)new [OCl] = 0.0120 mol/(0.080 L + 0.080L) = 0.0750 M

Hypochlorite is the conjugate base of a weak acid, so it hydrolyzes:

OCl + H2O !

HOCl + OH

I 0.075 - 0 0

C -x - +x +x

E 0.075 -x - x x

pOH = log(1.61x104) = 3.79pH = 14 3.79 = 10.21

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 1

pH

mL OH

added


43/43


9.

45.0 g of solid calcium carbonate is added to 1.25 L of an aqueous hydrochloric acidsolution. The hydrochloric acid solution has a density of 1.13 g/mL and is 25.7% acid bymass. The solid calcium carbonate reacts with the acid to yield liquid water, aqueouscalcium chloride, and carbon dioxide gas.

a)


CaCO3(s) + 2 HCl (aq) H2O (l) + CaCl2 (aq) + CO2(g)

b)


? mol HCl

L=

25.7 g HCl

100 g soln!

1.13 g soln

mL soln!

1000 mL

L!

mol HCl

36.45 g HCl

=7.97 mol/L

Answer: __________________________________

c)


The question implies that there is excess HCl (i.e. CaCO3is the limiting reagent).

? initial mol HCl =1.25 L soln!7.97 mol HCl

L

= 9.96 mol

? mol HCl reacted = 45.0 g CaCO3 !mol CaCO3

100.1 g CaCO3!

2 mol HCl

1 mol CaCO3

= 0.899 mol

? mol HCl leftover =9.96 mol 0.899 mol

=9.06 mol

? mol HCl leftover

L=

9.06 mol

1.25 L

=7.25 mol/L

Answer: _____________________________

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