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CHM 1321 Study Guide - Final Guide: Activation Energy, Organic Chemistry, Alkane Stereochemistry

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violetdolphin797
21 Sep 2014
School
University of Ottawa
Department
Chemistry
Course
CHM 1321
Professor
Greg Flynn

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CHM 1321 Full Course Notes
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CHM 1321 Full Course Notes
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Document Summary

Markovinikov: most stable, hydrogen on the least substituted position. Anti-markovinikov: hydrogen on the most substituted position, regents can be used to create these despite them being a less stable intermediate. Regiochem is a result of asymmetry in the transition state. C-h bond forms slowly: it develops the positive charge on the carbon. Reaction will be faster if the activation energy is lower. Each bh3 can react with three different double bonds. The product borane is converted into another product: h2o2, h2o, naoh. Stereochemistry (not important in markovinikov, only important in antimarkovinikov) H and b add at same time: therefore add to the same face of c=c. X = halogen: use radical reactions. X-y can break bonds by moving electrons. Heterolytic cleavage: atoms get different numbers of electrons. Homolytic cleavage: atoms each get 1 electron, single barbed arrow. Radicals: have unpaired electrons, unstable and very reactive, involve special mechanisms called chain reactions. Product of one reaction becomes the start of another.

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Related Questions

18. Circle the fatty acid in each pair that has the higher melting temperature.
(a) 18:1∆9 vs 18:2∆9,12
(b) 18:0 vs 18:1∆9
(c) 18:0 vs 16:0
19. Categorize each of the following as an aldose, a ketose, or neither.
H H H H H
HOH OHOH HOHO
O HOH HOH HOH HOH HOH HOH HOHO HH
H H H H H
(a) (b) (c) (d) (e)


20. What is the most significant chemical difference between triacylglycerols and glycerophospholipids that leads to their different functions?


21. What is the effect of a double bond on the fatty acid structure?



22. (a) When relatively high concentrations of fatty acids are suspended in water, they form structures known as ________. (b) When relatively high concentrations of membrane phospholipids are dissolved in water, they form structures known as ________. (c) Why are the structures listed in your answers to (a) and (b) above energetically favored?


23. What is the role of cholesterol in terms of membrane fluidity?


24. There are two reactions in glycolysis which involve the isomerization of an aldose to a ketose or vice-versa. What enzymes catalyze those two reactions?


25. The simple sugar that is used as the reference for naming D and L states of sugars is:



26. Draw D-glucose and a C-3 epimer of D-glucose.






27. Draw the cyclic forms of D-glucose and indicate the anomeric carbon with a *. Name the forms.




28. Describe the structure of starch. Include the identity of its subunits and the details of the bonds between them.




29. Why can humans not use cellulose as a nutrient?




30. Circle the following fatty acid that would have the lowest melting point. Put a square box around the fatty acid that is unlikely to be a natural product. Lastly, Name the fatty acid that you have not Circled or Boxed.

31. In cells, fatty acids are stored as triacylglycerols for energy reserves. Draw the molecule that fatty acids react with to form these energy storage molecules.

INTRODUCTION

Many transition metal cations can have more than one possible charge (Worksheet 1). Differently charged species of the same element can have different chemical and physical properties. Knowing the charge can allow separation of the different ions based on their properties. For example, Cu2+ is blue and stable in solution, while Cu+ is colorless and reacts with oxygen. Hemoglobin contains iron as Fe2+, but it is inactive at binding oxygen when the iron gets oxidized to Fe3+. There are many similar situations in which it is important to always properly indicate charges of ions.

This laboratory experiment uses the difference in chemical properties of Fe2+, iron(II), and Fe3+, iron(III), to quantify the amount of each present in a solution of unknown concentrations of each. You will first determine the amount of iron(II) in your sample by titrating with a reagent that does not react with iron(III). You will then titrate a second sample after converting all the iron(III) to iron(II) in order to determine the total iron present. The percent composition of Fe2+ in the unknown mixture will be calculated.

BACKGROUND

The concentrations of both iron(II) and iron(III) ions in a solution can be determined by titration with potassium permanganate. The reaction is an oxidation-reduction reaction, or redox, for short. A brief introduction to oxidation-reduction reactions is given in the background of the “Acids and Bases” experiment. The permanganate ion effectively oxidizes iron(II) to iron(III) in an acidic solution while being reduced to manganese(II) ion. The balanced net ionic reaction is:

5 Fe2+(aq) + MnO4–(aq) + 8 H+(aq) → 5 Fe3+(aq) + Mn2+(aq) + 4 H2O(l)

Iron(III) is not oxidized by the permanganate ion, and thus does not react. Thus in order to determine the concentration of iron(III) ions, they must first be reduced to iron(II) ions. Zinc metal is used as the reducing agent, also under acidic conditions.

Zn(s) + 2 Fe3+(aq) → 2 Fe2+(aq) + Zn2+(aq) (reduction of the Fe3+)

Zn(s) + 2 H+(aq) → Zn2+(aq) + H2(g) (a side reaction that oxidizes excess Zn)

The Zn2+ formed does not interfere with the subsequent titration because Zn2+ is not oxidized by permanganate. Notice that converting all the iron(III) to iron(II) means that the total iron concentration ([Fe2+] + [Fe3+]) is titrated, not just the iron(II) originally present.

Techniques

This is a lab will utilize several of the techniques introduced in the experiment “Laboratory Techniques and Measurements,” the procedures for which are given in Appendix B. Poor laboratory technique and misuse of the glassware will result in poor data results, which will affect the grade you receive on the laboratory report. In order to use your time efficiently in lab, review how to properly:

rinse glassware prepare a standard solution use a volumetric pipette

weigh by difference set up and use a burette use a graduated cylinder

heat samples on a hot plate

Analysis of Iron by Oxidation-Reduction Titration

This lab uses the common quantitative technique of titration. The only difference between the titration you will be doing in this lab and that done in the Molar Mass of a Known Acid lab is the type of reaction used: this lab will use a redox reaction in place of the acid-base reaction performed in the previous experiment.

In order to determine the concentrations of iron(II) and iron(III) ions in a solution containing both ions, two portions of the same sample must be titrated separately. This first titration will determine only the iron(II) concentration. A second sample will be treated with zinc metal in order to reduce the iron(III) to iron(II). The resulting solution will be titrated with potassium permanganate. The result of this titration will give the total iron concentration in the sample. The difference between the first and second titration is the equal to the iron(III) concentration.

In this titration, potassium permanganate serves as its own indicator. The intense purple color of the permanganate solution becomes colorless when the permanganate is reduced to manganese(II). Thus, as iron(II) is oxidized with the addition of the permanganate solution from the burette it will impart a purple color that will fade. However, once there is no iron(II) left in solution a faint purple color will remain, marking the endpoint of the titration. This color can be slightly altered by the presence of iron(III), which is yellow in solution. Remember that iron(III) is generated by the reaction between iron(II) with permanganate, increasing the yellow appearance of the solution and which can interfere with the detection of the endpoint. Phosphoric acid is added to help minimize this effect.

pre lab questions:

You are part of a team working on the development of a process in which a mineral species (labeled A for proprietary reasons) undergoes a reaction to form a new pigment to be used in house paints. In a series of experiments in a large well-mixed stirred tank reactor, you fill a tank with a known quantity of an inert liquid, bring the liquid up to a specified temperature, add a known quantity of A, and measure the concentration of A in the tank as a function of time. The reaction gives off heat as it progresses, but cooling water circulating in a jacket around the reactor keeps the temperature of the reacting mixture constant. The following data are recorded.

Concentration of A, CA(mol A/L)

t(min)

T = 94°C

T = 110°C

T = 127°C

T = 142°C

10

9.30×10−2

5.19×10−2

2.10×10−2

9.87×10−3

20

6.17×10−2

2.35×10−2

1.33×10−2

5.55×10−3

30

4.41×10−2

1.91×10−2

8.15×10−3

3.97×10−3

40

3.12×10−2

1.45×10−2

5.92×10−3

2.45×10−3

50

2.58×10−2

1.01×10−2

4.48×10−3

2.27×10−3

60

9.30×10−2

9.50×10−3

4.36×10−3

1.83×10−3

A research article indicates that concentration of A should vary with time according to the following expression:

CA(t)=11CA0+kt

(1)

where CA0 (mol/L) is the initial concentration of A in the reactor [CA(t=0)] and k is called the reaction rate constant. Despite being called a constant, k is a strong function of the absolute temperature in the reactor:

k(T)=k0 exp−EaRT(K)

(2)

In this equation (known as the Arrhenius equation after the Swedish chemist who proposed it), k0 is a constant, Ea(J/mol) is the reaction activation energy, and R=8.314 J/(mol·K) is the universal gas constant. Your task will be to verify that the expressions for CA(t) and k(T) fit the data, and if they do, to determine the parameters CA0 and k at each temperature and then the constants k0 and Ea.

(a)

What are the units of k, k0, and Ea if CA is in mol/L and t is in min?

(b)

Transform Equation 1 into an equation of the form y=at+b, so that if Equation 1 is valid, a plot of yvs. t would be a straight line. How would you determine CA0 and k from the slope and intercept of the line?

(c)

Create an Excel spreadsheet with the structure shown as Rows 1-10 in the figure at the end of this problem statement, and fill in the data table in Columns A-I. Then create the four scatterplots shown in Rows 15-21. In the “Trendline” options of each plot, check the boxes for “Display equation on chart” and “Display R-squared value on chart” but not the one for “Set intercept.” R2 is the coefficient of determination (it has several other names as well), and provides a measure of how well a straight line fits a set of data: the closer it is to 1, the better the fit. What can you conclude about Equation 1 from the four plots?

(d)

From the four trendline equations, calculate the values of k and CA0 for each of the four experimental temperatures and fill in Columns B-I in Rows 12 and 13 of the spreadsheet.

(e)

Enough A was initially added to the tank to make the initial concentration CA0=0.25 mol/L, yet you calculated four different values of CA0 in Part d. How do you explain this result?