Blog 9.2 LeChatlier's Principle (Due April 17th)

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?

Blog 9.1 Heat of Solution (delta H), Using Table I. Due Date April 5th (Thurs)

Post-Lab Questions: (Blog Questions)

1.)   Was your solution process endothermic or exothermic?  Describe the process using terms such as: direction of heat flow, system, and surroundings of the system.

 

2.)   What are the possible sources of error that cause a difference in the value that you got, and the value that was published on the reference tables (table I)? (Human or calculation error are not acceptable.)

 

3.)   How would your numbers for q, moles of solute, and ultimately ∆H (q/mole), be affected if…

a.)   The room temperature was 10^oC colder.  Explain.

 

b.)   You added less chemical, but knew the mass you added.  Explain.

 

c.)   You added 40 mL of water but thought you had added 50 mL.  Explain.

 Enrichment:  (1 pt)

In Florida, when the weather report is calling for freezing temperatures, orange farmers will mist the fruit trees with water overnight in order to prevent damage to the tree and fruit.  The water being sprayed on the tree freezes, but as it does so, this protects the tree from damage.  Explain why this works.

Blog 8.1 Hydrocarbon properties and uses (Due Thursday March 15th)

Hydrocarbons (alkanes, alkenes and alkynes) are very important substances that we use for many things. We drill for and pump crude oil which is a mixture of lots of different hydrocarbons. You need to answer these questions about hydrocarbons, you will have to do some research to be able to answer these questions. Please ignore the temptation to copy and paste your findings into your blog.

First answer these questions:

What is crude oil? What components are in the mixture of crude?

How to we separate the components of the mixture? What physical properties do we use to do that separation?

How do the properties of hydrocarbons change based on their size? How does this influence the boiling point of something small like methane compared to something large with 30 C's or more?

Research one or more of the following of interest to you.  Write 2-3 paragraphs summarizing your findings.

a.     The discovery of oil in the US and the location of the first drilling for oil ever done.

b.     How oil is drilled out of the ground.

c.      The extraction of oil from “oil shale” and “oil sand” deposits.

d.     The refining process used to extract particular components out of “crude oil.”

e.      The likelihood of finding natural gas, oil or coal deposits in Western NY.

f.       Why oil prices have been rising lately, and how the global oil trade is run.

Lab 7.3 Reactivity of Metals

1.  Answer the lab question on the first page of this lab.  CITE EVIDENCE FROM YOUR OBSERVATIONS! Make sure you explain thoroughly.

2.   Why do elements in the same column on the Periodic Table tend to have VERY SIMILAR properties?  Explain in terms of electron configuration! Use specific examples from your groupings.

3.   Describe what happens when an atom of sodium atom interacts with an atom of a nonmetal.  In your description, indicate:

a.   Whether the sodium atom loses or gains electrons,

b.   Whether the sodium atom becomes a positive or negative ion,

c.   The electrical charge of the sodium ion,

d.   Which noble gas sodium’s electron configuration becomes like,

e.   Whether the sodium atom becomes more or less stable as a result of reacting.

ENRICHMENT: 

The elements Li, Na and K are too reactive to be found in nature as pure elements.  Research how chemists obtain pure sodium in the form like we used in lab.

Lab 7.2 Periodic Trends Activity

These three trends are more challenging to explain, explain them:

·        Atomic radii trend going from left to right across a period.  The heaviest elements in a period have the smallest radii. WHY?

              ·        Electronegativity decreases when you move down a group. The larger the atom in the same group, the less it attracts electrons. WHY?

·        Ionization energies as you go from left to right across a period.  It kind of makes sense that it is harder to strip an electron from a metal than from a non-metal, but WHY is this so?

The key to explaining these trends is to figure out what “nuclear charge” is, and then to figure out what it has to do with these property trends.  Google will be a big help if you ask the right question in the search bar!  Good luck, and of course, talk with your teacher as needed!



Why do you think the trends are referred to as being "PERIODIC." Hint the word periodical is sometimes used with magazines and newspapers that are delivered at regular intervals.

Blog 7.1 Flame Tests and Emission Spectra

Conclusion:

1.  After seeing the spectra of various elements in this lab, why do you think an element’s spectrum is often called its “fingerprint?”   Explain using the terms ground state, excited state, and electron configuration.

2. Explain how a spectra is formed. Make sure to include the process and the steps that occur. This is important that you can describe what happens during the changes between ground and excited state, and how energy is released and absorbed.

ENRICHMENT:

1.  Research the discovery of the element Helium, and why it is given the name it has.

2.  Find out how astronomers use what is called a “red shift” or a “blue shift” to know whether a galaxy is moving towards or away from our galaxy.  To do this:

a)  Explain what blue shifts and red shifts are, and what they have to do with an element’s spectrum.

b)  Explain how the ratio of blue shift to red shift galaxies is used as evidence that the universe is expanding.

c)  Find out what Sir Edwin Hubble had to do with all this.  

Lab 6.1 Double Replacement Reactions

In our lab we looked at many different scenarios where a double replacement reaction either resulted in no apparent change, or the formation of a precipitate.

First, take a look at your predictions. Where they all accurate? If not explain which ones did not match up. See if you can figure out what happened. There was one trial that had results that did not match up with the expected prediction. Where you able to find it, which one was it? What do you think the insoluble product was, this will go against what table F tells us!!

Write a procedure on how to write a double replacement reaction. You can do this with bullets or paragraph form. The steps that you must have include: finding and writing the formulas for the products, balancing the reaction, and finding the precipitate. Describe theses steps (and more if you need them in detail, don't just give me a list of what I just gave you!!)





Precipitation reactions are very important in water treatment and purification. Find a contaminant that is removed from waste water before it is processed back into nature using a precipitation reaction (hint do a google search). See if this reaction is consistent with the information on Table F (it depends on the ion that is used). Sulfate is an ion that is often used to form precipitates, using Table F why is this a good choice.