Lab 10.3: Titration and Colligative Properties (Due Wed 5/4)

Titration Section

In this part of the experiment you had to do a titration to determine the concentration of the base (NaOH). In the process of the titration you produced three separate pieces of data and calculated the deviation.

Describe how far apart your different measurements were. Did they vary a lot? Were you surprised in how much variation that you found. Can you think of any ways that your actions during the titration may have caused issues with your values? What could you have done to make your trials more consistent across the board?

Colligative Properties Section

In this section you were asked to investigate some real examples of the colligative property at work.

Antifreeze is used in engines as a coolant. They take advantage of both the freezing point depression and boiling point elevation. Come up with a reason why each of these are important based on the variable climate that we live in.

The reason these processes work is due to the attractions that take place between the solute molecules and the solvent molecules. Describe how the attractions cause the freezing point depression and how they also cause the boiling point elevation.

Enrichement:
 Find another application of the colligative properties. Find a real world use, some hints: One is used in the making of a tasty treat that we will actually do later in the year. Describe how the process works for the example that you find.

Lab 10.2 - Solubility vs Temperature

In this experiment you used potassium chlorate to make a solubility curve that is similar to the ones that are found on Table G.

Look at the solubility curve on table G 

Compare your solubility curve to the actual solubility curve. Compare any parts that are similar or different. Obviously you used 10g of solvent instead of 100g, so explain how that affected your graph.

What things made a significant difference in how quickly the KClO3 dissolved. If you wanted to get something to dissolve quickly, what things can you do in order to make it happen. The more important question is: Why does this happen at the particle level, what does particle collisions and attractions have to do with this? Does surface area relate to this at all, and if it does what can you do to change that variable to make it happen quicker.

Describe how the terms unsaturated, saturated, and super saturated apply to the experiment. At what point was the solution saturated, and at what point was it unsaturated. I will tell you now that with potassium chlorate in this experiment, you never formed a supersaturated solution, it precipitated out before that happened.

ENRICHMENT: Find out how rock candy is made. I am sure you can find a recipe very easily, but I want you to apply this to chemistry using the vocabulary we have learned. This is a little more difficult task than just finding the recipe. If you want make it, try it, it is delicious.

Lab 10.1 - Solvents (Like Dissolves Like)

Results:

1. Which samples are definitely polar?  How do you know?

 

2. Which samples are definitely non-polar?  How do you know?

 

3. From the data, what can you conclude about the polarity of ethanol?

 

4. Would you expect ethanol to dissolve in water?   How about in hexane?

 

5. Classify the following as non-polar or polar molecules.  Then, predict their solubility in each solvent.

	Type of Molecule	Solubility in Water	Solubility in Hexane
NH3
I2
HCl

6.  Why do ionic materials dissolve so well in water, but not in hexane?

Enrichment: Atmospheric gases such as oxygen, nitrogen and carbon dioxide are capable of dissolving in water. Make a prediction regarding how much you expect these gases to dissolve based on their polarity. See if you can find or think of at least one reason why oxygen and carbon dioxide need to be able to dissolve in water for aquatic life to flourish.

Blog 9.2: LeChatelier's Principle

Station One

 Explain the shift that happened when HCl was added.

 1.    Explain the shift that happened when the system was heated, based on the location (products side or reactants side) of “heat energy” in the reaction.

2.   Describe how the Delta H (heat of reaction) shows whether the reaction is endothermic or exothermic. Relate this to potential energy and also the + or - sign of delta H.

 3.    

a. What does Table F say about the interaction between Ag¹⁺ ion and Cl^1- ion?

b. From your observations about what happened when you added AgNO₃, what evidence do you have that the Table F interaction happened?

c. Explain the shift caused by adding AgNO₃.

Station Three Processing Question:

6.  In terms of pressure changes, explain how your observations help to make sense of the fact that a carbonated beverage begins to effervesce (release gas) as soon as the bottle is opened.  (A chemist might say the reaction “shifts to the right” as soon as the container is opened!)

ENRICHMENT: 

Chickens Lose Equilibrium…Problem Solved Applying Le Chatelier

By David B. Brown & John A. MacKay III

Chickens cannot perspire, so when they get hot, they pant.  This seemingly trivial fact led to a serious economic loss for egg producers.  In hot weather, chickens lay eggs with thin shells that are easily (and frequently) broken.  A little reflection shows that this is an inevitable consequence of Le Chatelier’s principle and the well-known carbon dioxide equilibrium system.

CO₂ (g)  <-->  CO₂ (aq) <--> H₂CO₃(aq) <--> H⁺ + (CO₃)^2-(aq) <--> CaCO₃(s)

(chicken breath) ------------- (chicken metabolism) ---------------------- (egg shell)           

When the chicken pants, the equilibrium is perturbed by the rapid loss of carbon dioxide.  Because this effect cascades through all of these equilibria, the effect is a loss of solid calcium carbonate, which ultimately produces weaker egg shells.

Ted Odom, while a graduate student at the University of Illinois, found the deceptively simple “solution” to this problem – give the chickens carbonated water.  Now the equilibrium has been perturbed in the opposite direction.  The addition of aqueous carbon dioxide shifts all of the equilibria to the right and results in stronger egg shells.  Moreover, the chickens seem to like the carbonated water, and there are rumors that they spend their spare time singing familiar singles about “spirit” and the “real thing.”  Philosophical questions about which came first are left to the reader, but in this case, at least, Le Chatelier’s principle comes before the egg (shell).

Questions:

1.)    What gas do chickens pant out?

2.)    When the [CO₂] decreases, which way does the equilibrium shift?

3.)    When the equilibrium shifts, what happens to the amount of the CaCO₃(s) (the egg shell) that is produced?

4.)    Explain why panting results in thinner egg shells.

5.)    What change could farmers make to assure thicker egg shells in hot weather?  How does this change take advantage of Le Chatelier’s principle?