Grade12 Chemistry
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Homework
Thurs., May 15 - 1) a) Use the molecular orbital theory to explain how metallic crystal lattices are able to conduct electricity in the solid state.
b)Another property of metals is their ability to reflect all colours of light. How can the same molecular orbital model for
metallic bonding explain this property?
2) Graphite is an allotrope of Carbon in which the carbon atoms form sheets of carbon in hexagonal cells with each Carbon sigma-bonded
to three other carbons. These macromolecules form flat sheets. The bond angles all are 120o.
a) What is the hybridization state of Carbon in graphite?
b) Are there any multiple bonds and resonance structures?
c) Does graphite have delocalized pi bonding?
If so, over how many Carbon atoms would they be spread?
d) Explain how it is that graphite conducts electricity.
3) Diamond is an allotrope of Carbon in which each crystal is a single macromolecule with each Carbon sigma-bonded to 4 other Carbons.
a) What is the hybridization state of Carbon in diamond?
b) Should diamonds be able to conduct electricity (don't test this at home!)
4) What intermolecular forces should exist in each of the following substances:
a) CH4 b) H2S c) HCl d) NH3 e) NaCl f)Na
5) Explain the trends in boiling points in the following graph with respect to the intermolecular forces and their relative strengths.
Wed., May 14 - Read over the molecular orbital theory reading and complete questions 1 to 4.
Visit the link in the reading assignment to Dr. Bader's website, if you are interested.
Tues., May 13 - 1) a) Describe the bonding orbitals (type, atomic orbitals that made them) for the compounds listed below.
Include any delocalized pi bonds and list the atoms over which the delocalized orbitals are spread.
b) Describe any problems with respect to lone pair electrons on any of these molecules.
c) Propose a solution to this problem.
C6H6 (Benzene), C2H3O2- (acetate), O3 (Ozone), SO3 (Sulfur trioxide)
2) Draw Lewis structures for the following molecules based on the evidence given. Include any resonance structures.
Also, describe the hybridization state of the central atom(s).
a) F-O-N-O O-N bond is 134 pm N-O
| N-O bonds are 129 pm | 125o F-O-N 105o
O F-O bond is 142 pm O
b) CH3ONO2
all three Oxygens are in the same plane
the three Hydrogens are not in the same plane
C-O-N bond angle is 105o
O-N-O (NO2 side of the molecule) bond angle is 125o
the O-N bond length for the oxygen bonded to the carbon is longer than the other two N-O bonds
c) H-C-C-C-O C-H bonds are 106 pm (left-most) and 108 pm (right-most)
| C-O bond is 121 pm
H the C-C bonds are 120 pm (left-most) and 146 pm (right-most)
the H-C-O bond angle is 120o
the H-C-C bond angle is 120o
d) HCONH2
the H-C-O bond angle is 125o
the H-C-N bond angle is 113o
the N-C-O bond angle is 124o
the C-N-H bond angle is 119o
the H-N-H bond angle is 119o
the C-N bond is 138 pm
Mon., May 12 - Study for chapter 3 test tomorrow. Work on chapter 3 self quiz and end of chapter questions.
You should be able to describe how the different pieces of experimental data lead to the refinement of the
model of the atom from the raisin bun model of Thompson to modern quantum mechanics, orbitals, and the wave
model of the electron. You should understand why the particle model of the electron was abandoned for the
wave model. You also should know the contributions of Thompson (senior), Rutherford, Bohr, Plank, Einstein,
DeBroglie, Heisenberg, and Schrodinger. You should be able to construct energy level diagrams and electron
configurations for neutral atoms and ions, describe orbitals, and describe quantum numbers.
You also should be able these four ways of describing electrons to each other and to the structure of the
periodic table.
Fri., May 9 - class notes for today
- Work on the chapter 3 self-quiz and the end of chapter questions.
- Answer the following:
1) Identify the types of bonds (sigma or pi) that are formed in each of the following molecules and for
for each bond state what atomic orbitals (hybridized or not) combined to make the bonding orbital:
a) H2O
b) C2H6
c) C2H4
d) C2H2
e) PCl3
f) H2CO3
2) The molecule XYZ has a single central atoms, X, with the two other atoms bonded to it.
The bond angle between the X-Y bond and the X-Z bond is 118o.
The X-Y bond length is 120 pm and the X-Z bond length is 100 pm.
a) What is the hybridization state of atom X? State the evidence that you used.
b) Does atom X have any lone pairs? State the evidence that you used.
c) Does atom X have any multiple bonds with either of the other two atoms? State the evidence that you used.
d) Look at the bond length table in the May 5th class notes. Can you identify the molecule with the
help of the data in that table and the answers to a, b, and c?
Thurs., May 8 - class notes for today
- work on the chapter 3 self-quiz and end of chapter 3 questions in preparation for next week's chapter 3 test.
Wed., May 7 - class notes for today
- a) Draw Lewis diagrams for the following formulas.
b) Count the number of lone pairs and bonds for each formula to generate a shape code for each molecule.
All of these molecules have one central atom to which the other atoms are bonded.
c) Describe (name) the shape of each molecule and try to draw a three-dimensional perspective sketch of each.
CH3F, CO2, SF4, SO2, PF6-, NH3,
BF3, SiF62-, H2O, ClF3, BrF5, XeF2, XeF4
Tues., May 6 - class notes for today
1) a) Draw a Lewis structure for nitric acid HNO3 (HONO2, in case you need a hint).
b) Can you draw any resonance structures for nitric acid? If so, draw each one.
c) Remember that our best estimate of the "real" structure is an average, or hybrid, of each of these resonance structures.
Resonance structures are only out best attempt to use the technique of drawing Lewis structures to represent something that
they were not designed to represent.
With that in mind, describe how electron density is likely to be distributed in this molecule.
d) What resonance structures can be drawn when nitric acid ionizes in solution to form the nitrate ion?
e) How will this affect the distribution of electron density of the molecule?
2) The superoxide ion, O2-, is an important ion in biology. The ion is an imporant weapon deployed by the immune system
against invading bacteria. Draw a Lewis structure for this ion.
3) BeH2 is a molecule that involves an atom with an incomplete octet. Draw the Lewis structure for this molecule.
4) a) Draw resonance structures for Sulfur trioxide, SO3, and the sulfate ion, SO42-.
b) Calculate formal charges for the atoms in one of the resonance structures for SO3 and SO42-.
5) Sulfur can accomodate expanded valence states in molecules such as SF6.
a) With this in mind, draw alternate Lewis structures for both Sulfur dioxide and sufate in which sulfur has an expanded valence
shell and in which the formal charges are lower.
b) What sort of evidence might we look for to determine if these alternate structures really are more in line with reality?
Mon., May 5 - class notes for today
- 1) a) Use the rules outlined in class today to draw the best structure for the carbonate ion (CO32-).
b) Calculate the formal charges for each of the atoms in the carbonate ion.
2) a) Use the same rules to draw 4 plausible structures for nitrosyl chloride (NOCl).
One of the three atoms is not a plausible central atom!
b) Calculate the formal charges for each structure and use them to help determine which structure is most likely to actually
exist in any abundance.
3) Draw two plausible structures for the polyatomic ion NO2+ and use formal charges to determine which is the most likely.
Fri., May 2 - Answer the following: pg 197, #9,10,11,13; pg 220, #6,8,12-15
- The following assignment can be used to improve your grade from the chapter 8 test: Chapter 8 Make-up.
It is due by Wednesday of next week.
- Start reading through the first of the organic chemistry nomenclature assignments: hydrocarbons
Thurs., May 1 - 1) Write electron configurations for the following atoms: P, K, Mn, N3-, Br1-, Cd2+, Pb2+, Pb4+
Wed., April 30 - Visit the Orbitron website.
Orbitals are described with letter symbols:
orbitals corresponding to: l = 0 are called "s" orbitals
l = 1 are called "p" orbitals
l = 2 are called "d" orbitals
l = 3 are called "f" orbitals
A "s" orbital in the first energy level (n=1) are called 1s
A "p" orbital in the third energy level (n=3) are called 3p
For orbitals with more than one possible orientation, each orientation is given relative to one or more perpendicular axes
(x, y, and z). I am not sure as to the correspondence between particular values of the quantum number "m" and particular
orientations, but this is not of much importance to us in this course in any case.
There are 3 perpendicular orientations for the p orbital, parallel to the x-axis, y-axis, and z-axis. Each of these
corresponds, in some way, to the three different values for the quantum number m that are allowed for this orbital type.
The three different orientations are indicated as subscripts on the orbital symbol (2px, 2py, 2pz)
Homework: 1) Describe the general shape of the first four orbital types: s, p, d, and f.
2) Describe the orientations that these four orbital types can adpot.
3) Describe how each of the orbital types from different energy levels differ; i.e., how does a 1s orbital
differ from a 2s and a 3s ect.
To answer question 3, look at the radial distribution function for each orbital type. This gives
the probability of "finding an electron" as the distance from the nucleus changes. How does the number of
radial nodes change as you go up in energy level?
4) What do the different colours represent in the orbitron images of a particular orbital? How does this relate to
the sort of wave that we might see in a guitar string?
Tues., April 29 - No Homework
Mon., April 28 - Study for the test tomorrow.
Fri., April 25 - Work on the chapter 8 end-of-chapter review (1,2,4-18,23,24,15) and self-quiz questions.
- Answer the following:
1) Describe the recipe for making a buffer solution with a pH of 3.5 using citric acid and sodium citrate.
Both the acid and the salt are solids at room temperature.
The buffer should have the capacity to effectively buffer the addition of at least 0.5 moles of acid or
base per litre of solution.
2) What would be the pH of the buffer after the addition of 0.5 moles of HCl to 1.0 litre of buffer?
3) a) Calculate the pH of 10.0 mL a 0.15 M solution of Hydrogen cyanate (Ka=3.5x10-4)
b) Calculate the pH of the solution in a) after the addition of 6.5 mL of 0.10 M NaOH.
c) Calculate the pH of the solution in a) after the addition of 15.0 mL of 0.10 M NaOH.
4) What are all the possible values of the quantum numbers l and m for an electron in the 3rd energy level (n).
5) What is different about the following pairs of orbits:
a) n=2, l=1, m=-1; n=3, l=1, m=-1
b) n=3, l=2, m=-1; n=3, l=2, m=2
c) n=3, l=2, m=-1; n=3, l=1, m=-1
6) Which of the quantum numbers states something about the electrons themselves rather than the orbits they are occupying?
Fri., April 11 - Hopefully you have been working on the end of chapter questions for chapter 7: 1 to 18 on pages 523 to 524.
- In addition, answer the following:
1) Calculate the pH of the following salt solutions:
a) i) 0.010 M Na3PO4 (Ka3 of H3PO4 is 4.2x10-13);
ii) Why do you not need to consider the reaction of HPO42- and H2PO41-?
b) 0.0010 M Al(NO3)3 (Ka of Al3+ is 9.8x10-6)
2) Will the following salts produce acidic or basic solutions?
a) Sn(NO2)2
b) NH4CN
c) Na2HPO4
Ka values: Sn2+=2.0x10-2; HCN=6.2x10-10; HNO2=7.2x10-4
Kb values: NH3=1.8x10-5
Thurs., April 10 - Answer the following:
1) Calculate the percent ionization of of a 0.25 M acetic acid solution (HC2H3O2(aq)) if the
pH is measured to be 2.67
2) A 0.05 M solution of acetic acid has a percent ionization of 1.878%. Calculate Ka for acetic acid.
Check this Ka against the textbook value in the appendix.
3) Calculate the percent ionization for a 0.5 M solution of acetic acid. Use the Ka from question 2 and an ICE
table to calculate the equilibrium H+ concentration. Use this to calculate percent ionization.
4) A 1.5 M solution of a mystery acid has a pH of 0.345; what is the Ka and percent ionization of this acid?
What is the identity of this acid likely to be?
5) Is percent ionization a constant with different initial acid concentrations?
Wed., April 9 - Answer #2 on page 508 and #3 on page 511
Use this database of thermodynamic constants to get data to answer the second question.
- Answer questions 1-20 on page 522 and 1-18 on pages 523 to 524 for a chapter 7 review.
- Answer #7 on page 568 and #13 on page 574.
Thurs., April 3 - Please read over section 7.7 in the text. If you did not take your textbook home, this hyperpyhysics link may be
useful to you. Take care if you try to find websites explaining entropy. There are a lot of them and many of them
do not do a particularly good job.
Once in the hyperphysics website, click on the bubble to the left of the page labelled "heat and thermodynamics." Once
there, you will see a link to "entropy" in the middle-right of the diagram.
- Remember that we will be in room 412 tomorrow to carry out the Ksp lab.
Wed., April 2 - Answer the following:
1) What is the difference between the terms solubility and solubility product constant?
2) If the solubility product constant of salt A is lower than that of salt B, will salt A necessarily have a lower
solubility? Explain.
3) What is the solubility of Silver chromate (Ag2CrO4) in:
a) pure water?
b) a 0.2 M solution of sodium chromate (Na2CrO4)?
Tues., April 1 - Answer the following:
1) Calculate the Ksp for AgBr if its solubility is 7.46x10-8 at 25 oC.
2) Calculate the solubility of MgCO3 at 25 oC if the Ksp value at this temperature is 6.8x10-6
3) a) Determine whether any of the following mixtures will cause a precipitate to occur and, if so, what mass of the
salt should precipitate.
b) Indicate in which, if any, of these situations will be at equilibrium.
i) 100 mL of 5.04x10-5 M Zn(NO3)2 is mixed with 100 mL of 9.50x10-7 M NaOH
ii) 100 mL of 6.02x10-7 M Zn(NO3)2 is mixed with 100 mL of 3.20x10-5 M NaOH
iii) 100 mL of 5.00x10-3 M Zn(NO3)2 is mixed with 100 mL of 7.50x10-6 M NaOH
The Ksp for Zinc hydroxide, Zn(OH)2, is 7.7056x10-17 at 25 oC.
Mon., Mar. 31 - Calculate equilibrium concentrations for the following system: H2(g) + Cl2(g) ---> 2HCl(g)
for the following initial conditions: [H2(g)]i [Cl2(g)]i [HCl(g)]i
a) 0.25 M 0.25 M 0.25 M
b) 4.5 M 5.5 M 0.0 M
c) 0.10 M 0.25 M 0.0010 M
All systems are at 0 oC, at which Keq is 4.4x10-2
Use the simplifications involving perfect squares and ignoring small values of 'x' where appropriate.
Write out the balanced equation, calculation of Q, and an ICE table for each question.
Test your equilibrium concentrations for each question.
Fri., Mar. 28 - Answer pg 481: #1,2,3,6,8
- We do not have a good handle on what the error range associated with the measurement of transmitance. For this reason,
I do not think that a propegation of error in our calculations is going to be as useful as it might be in assisting our
decision making process. However, there are a few things that we can do to help ourselves out.
First of all, we must keep sight of what we are trying to accomplish in this lab:
we want to verify that the equilbrium epression evaluates to the same value for each set of initial concentrations.
To do this, we really need to know what the range in experimental error is to decide whether the disparate numbers that we
all will get really do represent the same number. One thing that we can say is that each of the dilutions made should have
been the same for each lab group, therefore, we ought to expect that each group should have measured the same transmitance
and the same calculated Keq for the same dilutions whether the equilibrium expression is a true constant or not.
Therefore, the range in values between lab groups for the same dilution ought to represent nothing but experimental error.
We can use this relative error to assign an error to the equilibrium constant values that we calculate for different dilutions
to decide if they could really be the same value.
So, I need each lab group to email me their Keq for each dilution so that we can calculate a reasonable error range.
One thing that we could do is propegate errors through our calculation of initial concentrations and compare those to the
range that we see in transmitance for the same dilution. If the transmitance range is larger than the calculated error for
concentration, we at least know that there is a significant error associated with our measurement of transmitance, as I suspect
there is.
Wed., Mar. 26 - Complete lab calculations.
Take care to keep the different concentrations straight.
Initial concentrations are those that exist after the Iron III nitrate and Potassium thiocyanate have been mixed. Obviously,
they only exist for a brief fraction of a second, if at all, as the reaction is quite rapid. However, we need to calculate
them so that we can calculate the equilibrium concentration of the two reactants. Since we are mixing equal volumes of the
two solutions, the initial concentrations are equal to half the pre-mix concentrations.
To calculate the pre-mix concentration of the Iron III ion, use the formula C1V1=C2V2
V1 = 10 mL and V2 = (10 mL + 15 mL)
C1 = the pre-mix concentration of the previous dilution.
For mixtures 2 to 5, we calculate the concentration of the FeSCN2+ ion from the transmitance.
Use the method on the bottom of page 2 of the lab handout.
Once you know this concentration, you can calculate the equilibrium concentration of Iron III and thiocyanate ions using
an ICE table.
Once all three equilibrium concentrations have been calculated, a value for Keq can be calculated for mixtures 2 to 5.
Tues., Mar. 25 - I have copies of the lab handout for everyone, but you can look at this copy to help you get ready.
- Consider the reaction A <--> B + C 
= +50 kJ at equilibrium.
The EA for the forward reaction is 100 kJ and the value for "A" in the Arrhenius
equation is 1000 for the forward reaction and 500 for the reverse reaction.
We will assume that both the forward and reverse reactions are elementary steps.
1) What is the activation energy for the reverse reaction (remember to convert all energies to J)?
2) Calculate activation energy for the reverse reaction.
3) Calculate the value for the rate law constant at 100 oC and 200 oC for both the forward and reverse reactions.
4) Which reaction experiences the greatest relative change in its rate with the increase in temperature?
5) Given your answer to question 4, in which direction will the equilibrium shift when the temperature is raised?
6) Is your answer to question 5 consistent with Le Chatelier's priniple?
- Those of you who have not yet completed the homework from last week, I will check them on Friday, so get them done!
Thurs., Mar. 20 - Answer the following: pg 442: #1; pg pg 444: #2,4; pg 447: #7; pg 449: #3,6,8
- Empirically, we know that the exponents in an equilibrium expression do match the co-efficients in the balanced equation, but
does this make sense theoretically given that the exponents and co-efficients do not necessarily match in the forward and
reverse rate law expressions?
Consider the reaction: 2A + 3B <--> 2C + D
It is not likely that the rate law expressions are rf = kf[A]2[B]3
and rr = kr[C]2[D]
In spite of this, at equilibrium, kf[A]2[B]3 = kr[C]2[D]
since K = [C]2[D]/([A]2[B]3)
Can we justify this theoretically? This may convince you.
Imagine that the mechanism is: A + B <--> 2E + F (slow step for reverse reaction)
F + A + E <--> 2C (slow step for forward reaction)
E + 2B <--> D
1) Is the mechanism consistent with the balanced equation?
2) Do the rate law expressions for this mechanism have the same exponents and the balanced equation?
Now, consider that at equilibrium, each of the elementary steps also must be in equilibrium.
Thus: (1) k1[A][B] = k4[E]2[F]
(2) k2[F][A][E] = k5[C]2
(3) k3[E][B]2 = k6[D]
We can re-arrange (2) to get [F] = (k5/k2)[C]2/([A][E])
and substitute this in for [F] in equation (1) to get
(4) k1[A][B] = k4[E]2((k5/k2)[C]2/([A][E]))
which simplifies to (cancel out one of the [E] from the numerator):
(5) k1[A][B] = (k4k5/k2)[E][C]2/[A]
multiply both sides of the equation by [A]
(6) k1[A]2[B] = (k4k5/k2)[E][C]2
We can re-arrange (3) to get [E] = (k6/k3)[D]/[B]2
and substitute this in for [E] om equation (6) to get
(7) k1[A]2[B] = (k4k5/k2)((k6/k3)[D]/[B]2)[C]2
which simplifies to
(8) k1[A]2[B] = (k6k4k5/k2k3)[C]2[D]/[B]2
multiply both sides of the equation by [B]2 and replace k6k4k5/k2k3 with k7
(9) k1[A]2[B]3 = k7[C]2[D]
which is what we wanted, because this can be re-arranged to:
(10) k1/k7 = [C]2[D]/([A]2[B]3)
which is our equilibrium expression.
Does this prove that the equilibrium expression always should have exponents that match the co-efficients? No, but
we did show that a random mechanism did produce the desired equilibrium expression, which leads us to suspect that
any other mechanism for any other reaction ought to produce the desired equilibrium expression as well!
Wed., Mar. 19 - Answer the following: pg 437: #6,7,4; pg 438: #7
Tues., Mar. 18 - Complete the chapter 6 review questions for tomorrow's test.
Mon., Mar. 17 - Complete your Rate Law Lab for tomorrow. You may email your results to me as Excel documents if you wish.
- Continue working on your chapter 6 review questions for the chapter 6 test on Wednesday.
Thurs., Mar. 6 - Complete analysis of lab results.
Wed., Mar. 5 - NOTE: the question on page 390 from Monday's homework should have been #2, not #1.
- Work on lab analysis: Updated Lab Results.
- I do not have lab results for group 4 for the catalyzed reactions. Could someone from that group please email me those results.
- Do NOT average results. Do you analysis by graphing each data pair (temp and time).
You may use Celcius temperature to graph the relationship between reaction rate and temperature.
Questions 11,12,&13 involve the data from part III: calculate a value for k for each datum point.
plot ln(k) versus Kelvin (absolute) temperature.
You should use your spreadsheet program (Excel, Quattro, and there are some freebies as well) to:
a) carry out calculations (show one sample of each calculation in your lab)
b) construct graphs
Tues., Mar. 4 - Lab Results for parts 1 and 2.
I am reporting the results as posted; I am neither supporting or refuting claimed precision.
Mon., Mar. 3 - We start a two-day lab in room 412 tomorrow.
- In addition to the homework from Friday, answer the following:
1) pg 390: #1; pg 391: #2,3 I-
2) Consider the following reaction: 2H2O2(aq) ---> 2H2O(l) + O2(g)
I-(aq) is a catalyst for this reaction.
The empirical rate law expression for this reaction is r = k[H2O2(aq)]
a) Why is this reaction not an elementary step?
The following is a proposed mechanism: H2O2(aq) + I-(aq) ---> OI-(aq) + H2O(l) (slow step)
OI-(aq) + H2O2(aq) ---> I-(aq) + H2O(l) + O2(g) (fast step)
b) Are the reactions in this mechanism likely elementary steps?
c) Does this mechanism add up to the over-all reaction?
d) Is this mechanism consistent with I-(aq) being a catalyst? Why?
e) Which of the species in the two reactions is a reaction intermediate?
f) Is the slow step consistent with the empirical rate law?
Think carefully about this: will [I-(aq)] change? If not, what can you do with it?
- Homework will be checked on Thursday.
Fri., Feb. 29 - Answer #2,3, and 5 on page 381 and #1 on page 387
Thurs., Feb. 28 - For the reaction: 2HgCl2(aq) + C2O42-(aq) ---> 2Cl-(aq) + 2CO2(g) + Hg2Cl2(s)
the following initial reaction rate data was obtained in three separate trials.
Trial Initial [HgCl2(aq)] (M) Initial [C2O42-(aq)] (M) Initial Reaction Rate (M/min)
1 0.105 0.15 1.8x10-5
2 0.105 0.30 7.1x10-5
3 0.052 0.30 3.5x10-5
Use the data to determine a rate law expression for this reaction in M/s and use the expression
to calculate the initial reaction rate for the initial concentrations of [HgCl2(aq)] = 0.35 M and
[C2O42-(aq)] = 0.75 M
Fri., Feb. 22 - Work on your Chapter 5 Test review questions.
Thurs., Feb. 21 - Work on your lab calculations.
Wed., Feb. 20 - There should be a good view of the lunar eclipse tonight, starting at around 8:45 PM
- Work on your lab calculations this evening. Follow the same rules for significant digits as before.
For the calorimetry calculations:
1) keep in mind that the volume of liquid in each experiment gives you the mass of water for mCpT
2) NaOH should be the limiting reactant for each experiment. n=m/mN or n=CV (V in litres)
- Error calculations can be completed separately.
absolute error: X 
a x has the same units as X
a tells you how far from X the actual value could be
relative error: X A A has no units
A = a/X (relative error = absolute error / number)
for Ti a
Tf b
T = (Tf-Ti) d d = a+b (add absolute errors for addition and subtraction)
D = d/T
mf F=f/m
Cpg G=g/Cp
q = mCpT h H = D+F+G (add relative errors for multiplication and division)
h = Hq (absolute error = relative error x number)
I will let you figure out the error in the molar mass of each element in NaOH so that you can
calculate the
- Remember: 1) that the efficacy of this procedure depends on our knowledge of the errors in our measurements
2) this procedure produces an error estimate for our calculations that is not as realistic as more sophisticated
statistical approaches that we might try out later (or not).
- We will do the Enthalpy of Formation lab tomorrow in room 412
Tues., Feb. 19 - Review for Chapter 5 Test: pg 355: #2-18; pg 356-357: #1-16
- Hess' Law lab tomorrow in room 412
- Class notes
Sat., Feb. 16 - Additions to the Enthalpy of Combustion Lab data have been posted as of 2100hrs Feb 16
- As you can see, we should consider what to do about outliers in our data (there is a considerable spread).
Normally, we would worry about outliers (data that depart significantly from the pattern exhibited by the majority of the data)
from the point of view that they represent mistakes that were made in carrying out the procedure, rather than random or
systematic errors that are an integral part of the procedure itself (errors that you cannot help but have as a result of the
way you were asked to carry out the lab).
We want to eliminate outliers for two reasons:
1) They alter our averages:
- our results are less likely to match accepted values.
- our compsrison of the combustion enthalpy values of the two alcohols will be less meaningful
2) They expand our error range:
- we decide whether the two alchols have different enthalpy of combustion values by seeing if the two
averages are more different than the size of error range. If the error range is too large, we might
decide that the two alcohols have the same enthalpy of combustion.
However, we can't just omit a value because we don't think that it is right. If you think that you have made a mistake,
you would, ideally, repeate the procedure a few times to make sure that your 'odd' result really is unrealistic. We did
not have time to do this, so you are going to have to exercise your best judgement. This time.
- If you realize that you made a mistake in your calculations, please send me updated data and I will repost your numbers.
Fri., Feb. 15 - Answer the following: pg 330: #3,4; pg 335: #5; pg 338: #7,8; pg 339: #1
Use the enthalpy of formation data starting on page 799.
- Class notes
Thurs., Feb. 14 - Answer the following from the textbook: pg 320-321: #4 (starts @ bottom of pg 320); pg 326: #1; pg 329: #5
- Have your textbook in class tomorrow.
- Class notes
Wed., Feb. 13 - Rather like election night, the results are starting to come in. At some point, we will give our lab groups
catchy names, but for now I will refer to them by first initials.
J&J: ethanol H = -38.1 kJ/g and Hcomb = -640.0 kJ/mol
methanol H = -24.3 kJ/g and Hcomb = -408.1 kJ/mol
L,H&H: ethanol Hcomb = -751.2 kJ/mol
methanol Hcomb = 462.8 kJ/mol
G,J&L: ethanol H = -16.5 kJ/g and Hcomb = -760.6 kJ/mol
methanol H = -15.2 kJ/g and Hcomb = -485.5 kJ/mol
J,M&C: ethanol H = -15.1 kJ/g and Hcomb = -697.7 kJ/mol
methanol H = -12.5 kJ/g and Hcomb = -400.1 kJ/mol
J&J#2: ethanol Hcomb = -711 kJ/mol
methanol Hcomb = -304 kJ/mol
A,J&C: ethanol H = -11.0 kJ/g and Hcomb = -505.1 kJ/mol
methanol H = -8.2 kJ/g and Hcomb = -263.8 kJ/mol
C,H&J: ethanol H = -16.7 kJ/g and Hcomb = -767.6 kJ/mol
methanol H = -12.8 kJ/g and Hcomb = -411.5 kJ/mol
D&B: ethanol H = -10 kJ/g and Hcomb = -480 kJ/mol
methanol H = -14 kJ/g and Hcomb = -440 kJ/mol
- I have updated the class notes for sections 5.2 and 5.3
- Complete calculations of molar and specific enthalpy changes for each alcohol in the lab.
One person from each group should email me the group's results.
These will be posted so that average values may be used for the discussion questions.
- Complete the rest of the lab. Try to have it ready to hand in on Friday, but the due date probably will end up being Tuesday.
The lab report will consist of: 1) a hypothesis
2) a sketch of the equipment
3) your original observations
4) answers to all of the calculation and discussion questions
5) your conclusion (do you reject or accept your hypotheses
Tues., Feb. 12 - Remember: only original observations taken at the time of the lab are to be handed in.
in future labs, I will be checking these as you carry out the lab and before you leave!
- Try calculating enthalpy values for your two experiments today.
- Make sure to bring your lab results to class tomorrow. We will calculate molar and specific enthalpy values in class
and will post these results to determine average values.
- Think about what might influence these ethalpy values for the two different alcohols. Remember that combustion (oxidation)
is a process that breaks a molecule apart, replacing high potential energy bonds (C-H and C-C in this case) with lower
potential energy bonds (C-O and H-O). Why ought these two alcohols have different molar and specific enthalpy of combustion
values (remember the structures for the two alcohols:
H H H
ethanol is HC-C-OH, while methanol is HC-OH
H H H
- Also consider the different experimental errors that might have occurred in your lab and how each would have
affected your results!
- The due date for the lab will be negotiated tomorrow.
Mon., Feb. 11 - Read sections 5.2 and 5.3 for Wednesday's class.
- class notes for sections 5.2 and 5.3 (we covered up to "Subscripts for Physical State" today)
- Enthalpy of Combustion Lab handout. Please print a copy for tomorrow's lab, if possible.
Thurs., Feb. 7 - Make certain that you are ready for your quiz on Monday.
- Answer the following using the equations: H = qsys
qsys = -qsurr
qsurr = mTCp
(the "p" subscript signifies that we are working at constant atmosphereic pressure)
The specific heat capacity (Cp) of water is 4.18 J/goC
1) How many Joules of thermal energy must be added to 1000 g of water in order to raise its temperature from
10 oC to 37 oC? (use the third equation only)
2) If 25.0 kJ of thermal energy is added as heat to 2500.0 g of antifreeze solution (Cp = 3.5 J/goC),
what will be its final temperature if its starting temperature is 20 oC?
3) a) What is the enthalpy change (H) of a chemical reaction if 5.00 g of reactant X
decomposing in a calorimeter containing 250.0 g of water produces a temperature change of + 20 oC?
b) What is the enthalpy change per gram of X?
- Consider the graph that we drew in class of what happens to a gram of water as it is warmed from -10 oC.
Identify one other assumption that we must make when performing a calorimetry experiment in addition to the three that
I gave you in class? Remember that we are using a temperature change in the water in the calorimeter to calculate how much
thermal energy the chemical reaction is releasing or absorbing!
- I will get around to posting class notes today some time.
Wed., Feb. 6 - Work on the Grade 11 Review
- Class notes, for those who were away today, will be posted later today or tomorrow.
Tues., Feb. 5 - Read section 5.1 (pg 298-305)
- Keep working on the Grade 11 Review
Mon., Feb. 4 - Study for the lab safety quiz tomorrow:
- safe practices rules
- your class room map of safety equipment
- WHMIS safety symbols for chemical bottles
- Continue working on your Grade 11 Review
Fri., Feb. 1 - Grade 11 Review
- Have a parent or guardian sign the course outline and be ready to show this to the teacher in class.
- Print off 2 copies of the first page of the safety contract and one copy of the second page.
Read the contract carefully and ask your parents or guardians to do the same.
Complete the bottom portion of one copy of the first page and return it to the teacher.
Place a copy of the first and second pages into your notes.
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