Week 14

Discuss one aspect of a comparison of a voltaic cell and an electrolytic cell.

In other words, we want to compare and contrast these two types of cells. The first person to respond choose one aspect to discuss and then the next person choose another aspect, etc.

Week 13 Question 2

Read the following article. What would you be looking for in a car that runs on a hydrogen-oxygen fuel cell?

http://phys.org/news/2014-03-nrel-hydrogen-fuel-cells.html

Week 13 Question 1

What is one concept that you are having difficulty with in Chapter 17? Why do you think that you are struggling with this concept? If you are not struggling with any topic, think of one that you think causes problems for a student and explain why.

Week 12

Start with the following question. We will make sure it is answered correctly before posting another question. If you believe that the person before you has not answered it correctly, give your answer and reasoning.

If CaCO₃, CaO and 1.0 M CO₂ are placed in a flask, will the reaction release heat energy or require heat energy at 25°C. The (delta)G°_rxn = 179.2 kJ and the (delta)H°_rxn is 131.4 kJ. Explain your reasoning!

                        CaCO₃(s)  <---->   CaO(s)  +  CO₂(g)

Week 11

A student is having issues with determining the pH at the equivalence point in a titration of a weak acid with a strong base. How would you explain the process of making this determination?

Answer this question and then write an issue that someone would have with the material in Chapter 16 so that the next student can explain that issue.

Week 10 Question 2

When doing a titration of a polyprotic acid, one starts with a solution of the polyprotic acid in a flask and incrementally adds titrant (strong base such as NaOH) to the solution. The pH can be calculated at various points in the titration, starting with zero added titrant. Some very useful points are the half-equivalence point, the first equivalence point, half way to the second equivalence point and the second equivalence point. 

Using the system of 25.0 mL of 0.050 M malonic acid, H₂C₃H₂O₄ titrated with 0.025 M NaOH, calculate the pH at the following points: 

    First person: zero added NaOH (initial point in the titration)

    Second person: first half equivalence point

    Third person:   first equivalence point

    Fourth person: second half equivalence point

    Fifth person:  second equivalence point

    Sixth person: after adding 150 mL of the NaOH

If we finish with this, I will put up a second system.

Week 10 Question 1

Determine the pK_x (meaning either pK_a or pK_b based upon whether it is an acid or a base) of the following species in solution, then choose another compound for the next person to determine the pK_xvalue.

(CH₃)₃NH⁺

Week 9 Question 2

Identify the following as an acidic, basic or neutral salt: CH₃NH₃Cl.

Choose another salt for the next person to answer.

Week 9 Question 1

What is the pH of a 0.10 M aqueous solution of CH₃NH₂? The Kb is 4.4x10⁻⁴.

Choose another acid, base or salt for the next person to answer.

Week 8

Identify the following compound as a weak acid, weak base, strong acid, strong base, acidic salt, basic salt or neutral salt and finally identify what species would be present in aqueous solution: HCNO

Choose another compound for the next person.

Week 7 Question 2

With Exam 2 next Tuesday, identify one topic that is causing you issues from Chapter 13 or Chapter 14. The next person should address the issue and then list their own issue.

For example: In a given mechanism, how would I know which step is the slow step if they are not identified but the experimental rate law is?

Week 7 Question 1

We are going to ask questions for the following reaction according to Le Chatlier's Principle. I will start with a question, the next person should answer it and ask their own question.

                                        CaCO₃(s) ⇌  CaO(s)  +  CO₂(g)                 ∆H = 131.4 kJ

Explain what happens to the value of the equilibrium constant when CaO is added to the reaction at equilibrium.

Week 6

We are going to answer a question and ask a question in each posting. First you answer the previous post's question and then you ask your own question. Let's try to keep it mostly conceptual (some math allowed) so that we can get at what these concepts mean.

A dynamic equilibrium arises when the rate of a forward reaction becomes equal to the rate of the reverse reaction. This is a process that occurs very often in chemical reactions. The ratio of the rate constant for the forward reaction, kf to the rate constant for the reverse reaction, kr is called an equilibrium constant, K. Thus K = kf /kr. 

If the rate constant for the forward reaction equals 1.2x10³ and the rate constant for the reverse reaction equals 4.1x10², what would be the value for the equilibrium constant? What do you think this means in terms of whether there are more reactants or more products at equilibrium?

Week 5

I am going to choose a term or a process from the Kinetics chapter (Chap 13) and explain it. The next person to post will give either an example or an illustration (an analogy about the concept). The next person will choose another term or process and we will keep alternating back and forth between an explanation and an example/illustration.

Starting:

Temperature impacts the rate of a reaction through increasing the speed of the molecules, which in turn increase the number of collisions. An increase in the number of collisions increases the probability that a reaction will occur since according to the Collision Theory, molecules have to collide (or nearly) in order for a reaction to occur between molecules.

Now the next person, give an example or an analogy!
After that the third person will explain another term and we will alternate back and forth.

Week 4 Question 2

Follow the link and read the article. Comment on at least one topic relating to chemistry.

http://alternativefuels.about.com/od/environmentalimpact/a/winterfuelecon.htm

Week 4 Question 1

4 NH₃(g)  + 5 O₂(g)   --->   4 NO(g)  +  6 H₂O(l)

I will write a question based upon rates of the above reaction. The first person will answer this question and then write a second question that the next person will answer and then write a question continuing on …..

So to start: What is the expression for the rate of disappearance of NH₃?

Week 3

Identify a specific topic from Chapter 12 that you are having a bit of difficulty with. The next person to respond should address that problem to the best of their ability and then identify their own issue. 

If you haven't noticed, I will kibitz  just to make sure that we are keeping on track. You might find it useful to go back in after you have posted to read everyone's postings and comments.
So I will start the process off:
"John" says that he is having difficulty with understanding the concept of how an insoluble solute affects the vapor pressure of a solution.

First notice that we are discussing the vapor pressure of a solution not a pure substance as we were in Chapter 11 and we will look at solutions made only from nonvolatile solutes so that it is only the solvent that will be entering the vapor phase.  At a particular temperature, a solvent has a certain amount of energy and there is a subset of the solvent molecules that have enough energy to enter into the vapor phase. When we add a nonvolatile solute and make a solution, those solute particles physically get in the way of the solvent molecules escaping into the vapor phase. Thus a smaller number of solvent molecules can evaporate at any given temperature and the vapor pressure will decrease with the addition of a nonvolatile solute.
A problem that I might have as a student: I am having a little difficulty with understanding the relationship between saturated solutions, supersaturated solutions and dynamic equilibrium.

(Now the next person explain this to me and then list your own issue)

Week 2 Question 2

Identify a specific topic from Chapter 11 (or from C105 that applies to Chapter 11) that you are having a bit of difficulty with. The next person to respond should address that problem to the best of their ability and then identify their own issue.

So I will start the process off:

"Jane" says that she is having difficulty with understanding why there is 1/8th of a corner atom inside a face-centered cubic unit cell. In response to this, I would explain:

A corner atom of a cubic unit cell is cut through by 3 planes (looking at the pictures in your text, page 521 and 522 will help you to see this as I try to explain). For example, a front plane, a side plane and a top plane. Since this "cuts" the atom in half each time, the first time I throw away 1/2 of the atom, leaving 1/2, the second "cut" throws away 1/2 of 1/2 leaving 1/4 and the third "cut" throws away 1/2 of 1/4 leaving 1/8 inside the cubic unit cell. It does not matter whether it is a primitive cubic unit cell, a face-centered cubic unit cell or a body-centered cubic unit cell, a corner atom will always have 1/8 of the atom inside one cubic unit cell.

A problem that I might have as a student: I don't understand how an increase in the external pressure causes the boiling point to increase.

(Now the next person explain this to me and then list your own issue)

Week 2 Question 1

Read the material at the link below: Chapter 13: Effective Learning and Teaching

www.project2061.org/publications/sfaa/online/chap13.htm

Do any of these concepts “speak” to you, either from the learning or teaching point of view? How does it change the way you view learning or teaching?

Week 1

What is your intention for this semester in Chemistry C106? Please don’t put it in terms of a grade, rather share what you hope to get out of the class. (Please post your response as a comment)