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acids & bases -- lewis theory & buffers

4/30/2014

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This post includes some final topics to finish up Acids & Bases.

Objectives:

1.  Define and describe the Lewis theory of acids and bases.

2.  Classify substances as Lewis acids or bases.

3.  Define and describe a buffer and, using equations, show how a buffer system works.

4.  Based on the hydrolysis of salts, predict the pH of salt solutions as acidic, basic or neutral.

In this video, there's a detailed review of Bronsted-Lowry theory, but that helps to clarify the Lewis theory of acids and bases.  He does talk about Bronsted-Lowry rather quickly, so you might want to check out my previous post about this theory.
Here's a super-short explanation, but I think it helps:
You may recognize the name Gilbert N. Lewis from bonding work and Lewis structures, and this theory  continues his focus on electron pairs.

To get a little history of Gilbert N. Lewis, here's the Wikipedia entry:

http://en.wikipedia.org/wiki/Gilbert_N._Lewis

Here's a worksheet with answers that touches on both Bronsted-Lowry theory and Lewis acid-base theory:

http://www.edmondschools.net/Portals/2/docs/Science/Dortch/Base%20Worksheet.pdf

A buffer is a weak acid and its conjugate base in an equilibrium system.  Here is a brief explanation:

The following video is longer (almost 20 minutes) and discusses buffers a little more in depth using a few older skills, including Ka.
You might not want to get too deep into buffers, but there are a few worksheets for this topic:

http://www2.ucdsb.on.ca/tiss/stretton/chem2/acidwk04.htm

Here are 10 multiple choice questions on acid-base buffers:
http://www.lghs.net/ourpages/auto/2013/3/28/53554610/Day3AcidsBasesBuffers.pdf

From http://www.science.uwaterloo.ca/~cchieh/cact/c123/salts.html  , this explanation of acid-base hydrolysis is presented:

"When weak acids and bases react, the relative strength of the conjugated acid-base pair in the salt determines the pH of its solutions. The salt, or its solution, so formed can be acidic, neutral or basic. A salt formed between a strong acid and a weak base is an acid salt, for example NH4Cl. A salt formed between a weak acid and a strong base is a basic salt, for example NaCH3COO. These salts are acidic or basic due to their acidic or basic ions..."

Here is a demonstration of the hydrolysis of various salts:
I appreciate the safety precautions stated at the beginning of the video.
Here's one lab procedure to test the pH of salts:
http://arapahoe.littletonpublicschools.net/Portals/7/Science/FirchauChem/Salt%20procedure.pdf

You might have to alter the salts used based on availability.

Here is another lab that might have to be edited.
http://slider-chemistry-12.wikispaces.com/file/view/30%20-%20Hydrolysis%20of%20salts%20prac.pdf/303261898/30%20-%20Hydrolysis%20of%20salts%20prac.pdf

Rather than use a full set of chemicals for a pair of students, you may want to set up stations that pairs can travel to and test the salt's pH.

Here's an acid-base Powerpoint presentation that you might find useful.  This link sends you to a very complete (long) PowerPoint presentation.  Warning: it has sound effects!
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=83&ved=0CDIQFjACOFA&url=http%3A%2F%2Fteachers.oregon.k12.wi.us%2Fehrlich%2FnewAcid%2C%2520Bases%2C%2520and%2520Salts%2520for%2520website.ppt&ei=LvJeU46iMojjsAS6ioGQAw&usg=AFQjCNFNIGgVV56AxkavdB7n6TCodoGCPA

Here's a worksheet with background and ending in questions:
http://chemistrybyscott.org/Worksheets%20&%20Handouts/Chem%201/Notes/Acid-Base/Salt_Hydrolysis_Outline.pdf

I have a few links listed under Teaching Resources that could be very useful -- if you haven't checked it out, the link is at the top of this page!

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired!  

*I'd love to hear from you!  Your feedback would really help me to focus on your needs!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Have a good end of the  week!

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acids & bases -- titration

4/24/2014

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Continuing with the topic of Acids & Bases, a major skill is acid/base titration. Titration is a method of reacting a solution of unknown concentration with one of known concentration -- this procedure is often used to determine the concentration of acid or a base (although it could be used with any other chemical reaction with a visible end point).

Objectives:

1. Determine the concentration of an unknown acid or base using data collected using acid-base titration.

2. Explain the information presented on a titration curve to determine the equivalence point during acid-base titration.


Here is an introduction of the basics of titration -- there's a bit of a sales pitch (sorry) but it's a good introduction:
Notice that he sets up the buret, or "primes" it, to prepare -- rinsing with water helps to remove any chemical residues, and rinsing with the titrant helps to rid of the excess water.

I like that he points out to read the bottom of the meniscus and the significant figures of the buret. 

At a high school level, you probably don't have enough volumetric pipets for a class -- simply measuring with a graduated cylinder is fine.

He mentions that after the initial "rough" titration to add all but 5 mL of that amount and then slow down to a dropwise addition.  This initial amount is sometimes called a "dump" or "dumping" that amount of reactant to the flask.

Here is another demonstration -- instead of using a volumetric pipet, he uses another buret.  He does go past the end point a few times -- I think it's just to show that if you do, it's not the end of the world.
I love the mural on the back wall -- who is it?  Sir Isaac Newton?

Here are a few acid-base titration lab handouts:

This lab is 3-pages, but a nice overview:

http://www.kentschools.net/ccarman/files/2009/08/4-4-Acid-Base-Titration-Lab-fy11.pdf

This lab is 3-pages, but the 3rd page contains supplemental problems and could be omitted:

http://www.wayzata.k12.mn.us/cms/lib/MN01001540/Centricity/Domain/703/Unit%206/LabTitration.pdf

And this final lab is 2 pages, so it could be copied to one 2-sided page (my goal for you):

http://www.sciencegeek.net/Chemistry/chempdfs/VirtualTitration.pdf

Here is a quick 3-minute video solving a strong acid / strong base titration problem:

The only thing I don't like is that he solves WITHOUT THE UNITS!  It's a very healthy habit to put the units in calculations -- yes, it's time consuming, but IT'S WORTH IT!  Don't stop making sure your units cancel!

OK, continuing on, here's another problem being solved with the units included:

Notice that instead of the formula MaVa = MbVb she is approaching the problem stoichiometrically, and the mole ratio is used, it just happens to be 1:1 -- approaching this way solves issues that are not 1:1.

I'm sticking with strong acid / strong base titrations as that is typical of an introductory high school chemistry course.

Here's one worksheet with answers:

http://misterguch.brinkster.net/PRA002.pdf

This is a little longer, but it has answers, too!

https://levesquec.wikispaces.com/file/view/titration+Worksheet.pdf

Oh, and here are some multiple choice questions with answers:

http://www.mrbeauchamp.com/AcidBaseRegentsReview.pdf

The pH changes in a mixture can be graphed producing a titration curve, a graph of pH vs. volume of acid or base added. Here's one discussion:
I appreciate his enthusiasm describing the color changes during an end point, and the difference between equivalence point and end point... :-)

Here's another discussion (about 10 minutes) to examine the topic of the acid-base titration curve:
This also presents another acid-base titration calculation, but the answer should round up to 0.047 M because the result if 0.0466...  His example involves a weak acid and involves the pKa, which I'm not focusing on here.

Here are directions for using Excel to plot a titration curve and a link to directions to find the equivalence point:

http://www.ehow.com/how_8405434_plot-titration-curve-excel.html

Well, my computer has been fixed so I should be back into a Sunday & Wednesday schedule.  Thank you for your patience!

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired!  

I have a few links listed under Teaching Resources that could be very useful -- if you haven't checked it out, the link is at the top of this page!  I just added one that has several Powerpoint presentations that you might find useful.

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might have a school vacation this week -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Have a good end of the  week!

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The next post is coming!

4/22/2014

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My computer is almost fixed and back home, but I won't be able to post on Wednesday... :-(

I hope to post my new blog page on Thursday, 4/24... keep your fingers crossed!
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4/20 post

4/19/2014

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Due to technical problems (my computer is sort of possessed right now), I won't be posting until Wed., 4/23/14 (I hope).

Have a good week!
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acids & bases - bronsted-lowry and K-acid

4/16/2014

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We're deep in that Spring Break time of year -- some are back in school, others are just going on vacation --  many are teaching Acids & Bases at this time, and so I am continuing that topic.

Objectives:

1. Use the Bronsted-Lowry theory to classify substances as acids or bases and identify conjugate acid-base pairs in chemical reactions.

2. Define amphoteric substance and give examples.

3. Calculate an acid dissociation constant, Ka, and a base dissociation constant, Kb, from concentration and pH measurements of weak acids or bases.

4.  Use Ka or Kb to determine the pH of a solution.

Here is a brief overview of the Bronsted-Lowry theory:
Amphoteric acids and bases are also known as amphiprotic.

It is typical to ask questions identifying the Bronsted-Lowry acid & base as well as the conjugate acid-base pairs.  The following video continues with this aspect of the Bronsted-Lowry theory:

Here are a few worksheets for practicing the skill of identifying the parts of an acid-base reaction based on the Bronsted-Lowry theory:

http://mtpleasant.glk12.org/pluginfile.php/12471/mod_resource/content/1/bronsted-lowry%20worksheet.pdf

http://www.ylhs.org/apps/download/2/2EtWc72labYZ2gKVd7DsBghqtTnrajyLCLvsKLdLCNjHmrdi.pdf/Worksheet%20-%20Bronsted-Lowry%20Acids%20and%20Bases.pdf

A topic for a more advanced students (in the AP range) examines weaker acids and bases.  Since they do not ionize (or dissociate)  completely in water, the equilibrium constant expression can be applied here to form Ka or Kb.  Here is one problem solving session:

He doesn't show the solution once a formula is set up -- from a formula with x's, he cross multiplies to get a value equal to an expression that is squared, then he takes the square-root of that value. 

Here is a short table with Ka values:

Picture
Here are some worksheets for student practice:

This is longer, but provides a little review of writing acid-base reactions:

http://mrfeathers.weebly.com/uploads/1/3/4/3/13437538/ka_kbworksheet.pdf


This provides a little Bronsted-Lowry review and answers at the end:

http://www.chemtopics.com/unit12/ppu12.pdf

Typical labs during an acid-base unit are titration -- I will talk about acid-base titration next week.

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired!  

I have a few links listed under Teaching Resources that could be very useful -- if you haven't checked it out, the link is at the top of this page!  I just added one that has several Powerpoint presentations that you might find useful.

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might have had a school vacation around now -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Have a good end of the  week!

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Acids & Bases -- Arrhenius definition and pH

4/13/2014

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There are several theories defining acid and base formulas and today I'm going to focus on the Arrhenius definition and the commonly used pH scale.

Objectives:

1.  Define and give examples of Arrhenius acids and bases; classify a solution as neutral, acidic or basic, given the hydronium-ion or hydroxide-ion concentration.

2.  Calculate the pH or pOH of a solution given the hydronium-ion or hydroxide-ion concentration.

3.  Calculate the hydronium-ion or hydroxide-ion concentration given the  pH or pOH.


Here is a brief overview (3+ minutes) of the Arrhenius definition of acids & bases:
The Arrhenius definition is essential to the idea of pH and its companion pOH -- here's an overview.  There is a little bit of extra dialogue, but overall it has the essential information:
I like his brief "ode to Jimi Hendrix" -- heehee. 

This next video slows down to get into the math associated with pH and pOH:
I like that he mentions that there is more than one way to get the answers.  It's a nice way to check yourself, too!

Notice that he guides students through using their calculators to perform calculations with scientific notation -- I've included that in my lectures to students b/c they tend to enter "x 10" to a power versus using the EXP or EE buttons on the calculator, ending up with an answer higher by 1 power of 10 -- help your students avoid this!

Here are a few worksheets practicing pH/pOH problems:

http://chemistry.about.com/library/pdfs/acidbase.pdf

http://misterguch.brinkster.net/PRA027.pdf

I will be relating pH/pOH to Ka and Kb in my next post.

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired!  

I have a few links listed under Teaching Resources that could be very useful -- if you haven't checked it out, the link is at the top of this page!  I just added one that has several Powerpoint presentations that you might find useful.

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might have had a school vacation around now  are around this time) -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Have a good week!


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acids, bases & salts -- intro

4/9/2014

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I hope I haven't skipped anything (or too much) in K&E, so next are Acids, Bases & Salts.  This unit will consist of several entries -- it uses several skills learned throughout the year, so it's good review! 

Objectives:

1.  List the general properties of aqueous acids and bases.

2.  Explain the difference between strong acids/bases and weak acids/bases and give examples.

This video provides a very short overview of the general properties of acids & bases:
I have made acid/base indicator using red cabbage, as well as other natural substances.  Red cabbage indicator provides a full spectrum of colors -- and it's very easy to make!

This movie is older (from the 80s), and I include it b/c I used it a lot in my classroom -- it's a broad overview (about 18 minutes) which is handy for starting the unit.  A few of the animations are a little blurry.
I like that it points out where on The Periodic Table acids and bases tend to be found (it's very quick), and it defines the Bronsted-Lowry theory of acids and bases.  In this, acids are proton donors and bases are proton acceptors.  I will further develop the idea of pH in my next blog post.

This video is from 2009 (30 minutes) so it's a little more current -- it might be a useful review video as it addresses pH and Bronsted-Lowry theory more in depth:
I think it was a tv program (with commercials) so it reviews every 8 minutes or so.  It does talk about pH again.  I like that it's very clear that he's wearing eye protection!

This video is a brief overview of strong vs. weak acids & bases:
A simpler laboratory to complete is to test the acid or base level in common household substances.

I have such a lab in my lab book "Chemistry on a Budget" which tests the presence of acid or base in common household substances, and it shows how to prepare indicators out of fruits and vegetables.

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired!  

The National Science Teacher Association (NSTA ) annual conference was this past week in Boston, Massachusetts.  If you attended the convention, please write me about it! 

I have a few links listed under Teaching Resources that could be very useful -- if you haven't checked it out, the link is at the top of this page!

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might be having a school vacation soon (spring breaks are around this time) -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Have a good rest of the week!

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the equilibrium constant and gibb's free energy

4/6/2014

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Continuing with the topic of Equilibrium, I'm getting into the equilibrium constant and  clarifying the definitions of enthalpy (delta H) and entropy (delta S) and applying that information to the spontaneity of reactions, summarized in Gibbs free energy (delta G).

Objectives:

1. Explain the nature of the equilibrium constant, define various variations of the equilibrium constant, and write an equilibrium expression for a reaction or Law of Mass Action.

2. Calculate the value of the equilibrium constant using the Law of Mass Action.

3.  Define entropy and and enthalpy.

4.  Explain how changes in entropy relate to a change of state, a change in temperature, and a change in the number of product particles compared with the reactant particles.

5.  Define Gibbs Free Energy, state the equation for Gibbs Free Energy, and examine various combinations of entropy and enthalpy that lead to a spontaneous reaction.


Here is a brief video providing a quick overview for defining equilibrium and writing a Law of Mass Action (or equilibrium expression):
What is not mentioned in this brief clip is that we only want substances that are considered to change in concentration, so that only includes gases and solutions (typically aqueous).  

The concentration values are in Molarity (M), but the units are not included in the expression.  This is one of the few instances where the units are not included in the calculation.  The brackets around the number, e.g. [0.5], are used for molar solutions.

Pure liquids or solids, even though they may be in a reaction, are not included in the equilibrium expression.

By the way, Keq is typically a general abbreviation for an equilibrium expression, but sometimes a  slightly  different symbol is used -- it's still the equilibrium expression but specific to water, Kw, acids, Ka, bases, Kb, and Ksp for solubility product.

This page is a nice overview of the equilibrium expression variations as well is calculating Kp:
http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Chemical_Equilibria/The_Equilibrium_Constant/Calculating_An_Equilibrium_Concentration_From_An_Equilibrium_Constant/Calculating_An_Equilibrium_Constant%2C_Kp%2C_Using_Partial_Pressures

Here's one worksheet to practice writing Keq expressions:
http://myclass.peelschools.org/sec/12/13397/Homework/Equilibrium/Worksheet%203%20-%20Writing%20equilibrium%20expression.pdf

Using this equilibrium expression, values for the substance concentrations can be calculated or used to determine Keq.  The following video (10 minutes) but shows a few examples using the ICE method.  ICE is I for initial concentration, C for change in concentration, and E for equilibrium concentration.
Here is a page of examples for your reference:
http://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Calculating_Equilibrium_Constants.htm

I may have mentioned enthalpy and entropy in previous entries, but I'm going a little more in-depths here -- enthalpy, or heat content, is represented by delta H -- it can only be measured by the release of energy -- calorimetry is the accurate and precise measurement of heat change for chemical and physical properties. 

Entropy is the disorder of a system. The law of disorder states that processes move in the direction of maximum disorder or randomness.  An easy to remember example is that of a bedroom starting cleaned and orderly and eventually getting messy and disordered, not to return to a state of order unless energy is exerted.

The natural tendency in the universe is to a state of lower energy (negative delta H) and higher entropy (positive delta S).

Here is a brief overview of enthalpy (delta H) -- the narrator later gets into adding reactions to get an overall delta H value -- Hess' Law states that if you add two or more thermochemical equations to give a final equation, then you can also add the heats of reaction to give the final heat of reaction -- a few examples are solved in this video as well.   Not all introductory courses get into Hess' Law problems, so use your discretion about covering it.  If it's not in the course syllabus and you cover it,  there might be complaints.
Here is a brief overview of entropy, a demonstration, and a discussion of how they are combined for Gibbs Free Energy.  Remember, goggles should be worn with every demonstration, and if you're going to try this yourself,  WEAR GOGGLES!

Here is a chart summarizing the combinations of delta H and delta S to produce delta G -- it's a very handy way to lecture about this topic:

http://3.bp.blogspot.com/_OdZZiyNKEoU/Sk1d2VNy_hI/AAAAAAAAAcw/V6HPs5Cfx64/s1600-h/Slide1.JPG

This page contains multiple-choice questions and answers:

http://fileserver.net-texts.com/asset.aspx?dl=no&id=10131

Here is another worksheet:

http://www.quia.com/files/quia/users/shwang01/2012/Chemistry/Worksheets/entropy_enthalpy_worksheet.pdf

The topics of enthalpy, entropy and Gibb's Free Energy can be covered during a thermodynamics unit.  Calorimetry labs are typical during this coverage -- I have a Calorimetry lab in my book "Chemistry on a Budget."

The National Science Teacher Association (NSTA ) annual conference was this past week in Boston, Massachusetts.  If you attended the convention, please write me about it! 

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might be having a school vacation soon (spring breaks are around this time) -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- both labs use the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired! 

Have a good week!


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equilibrium & le chatelier's principle

4/2/2014

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Sunday's post was mainly about Kinetics, so today I'm getting into Equilibrium.

Objectives:

1.  Define chemical equilibrium in terms of a reversible reaction.

2.  Identify physical processes and chemical reactions that go to equilibrium and those that go to completion.

3.  Describe Le Chatelier's Principle and predict changes in a chemical equilibrium system due to changes in (a) concentration, (b) temperature, (c) pressure and (d) the addition of a catalyst.

4. Explain the requirements in The Haber Process (or the Haber-Bosch process).

5.  Describe the common-ion effect.


This is a brief explanation of equilibrium with a very clear animation:


I am including this explanation as well because it will be referred to in subsequent segments:

To summarize, for a dynamic equilibrium to be established, there must be a closed system so that reactants and products do not leave but continue to react.

If the reactants or products leave the system, a reaction will continue to completion and eventually stop.  This can occur when a gas leaves a system (sometime bubbles are formed) or when a solid precipitate settles out of a solution.

Le Chatelier's Principle explains shifts in the equilibrium system due to changes in concentration, temperature, pressure and the addition of a catalyst, and the eventual establishment of a new equilibrium.  This all comes back to the idea of collision theory.

The following video continues with the previous explanation with the picture of digging and filling a hole:
It continues with the following installment:
Just to review, exothermic reactions release energy as a product (right side of the reaction), and delta H has a negative value.  The energy value is given a negative sign because it is being released or lost by the reaction.

Endothermic reactions absorb energy as a reactant (left side of the reaction), and delta H has a positive value.

Putting the energy in the reaction equation (simply as Q) makes it easier to  predict the direction of the shift if you think of the heat (Q) similarly to a reactant or product.

 One important application of Le Chatelier's principle is The Haber Process, explained in this video --  there's 1 minute of introductory credits (snore), but this clip continues right after that:
Here is another video that talks about the societal implications of The Haber Process -- this narrator gets bleeped a few times (sorry) when talking about the development and use of chlorine and mustard gas for use as a weapon during  WWI.  He also talks about current environmental impacts due to runoff of chemical fertilizers.
It is being referred to as the Haber-Bosch Process here.  BTW, the history of chemistry offers a great deal of researchable material for your students -- I'll talk about it in another post.

Another phenomenon is the Common Ion Effect -- the straight definition in textbooks can be confusing, so here is a short video with animation:
Here are a few labs where Le Chatelier's Principle is demonstrated:

This uses the colored compound CoCl2:

http://www.pleasanton.k12.ca.us/fhsweb/morris/chemlab/RatesEqu/Lab%20-%20Cobalt%20Chloride%20Equilibrium.pdf

This is a lab based on the acid-base indicator Methyl Orange:

http://www.austincc.edu/dsackett/CHEM1412/lab/1412exp20.pdf

A very simple demonstration is that of yeast being used as a catalyst to speed up the decomposition of hydrogen peroxide (H2O2) to produce water and gaseous oxygen -- if performed in a test tube, a glowing wooden splint (not flaming) will reignite when inserted into the gas.  You might want to put an index card over the end of the test tube to trap the gas.  DO NOT USE A STOPPER TO TRAP THE GAS!  The gas pressure would build up and the stopper could shoot out, maybe into someone's eye!

Here are some worksheets regarding Le Chatelier's principle:

http://www.greatneck.k12.ny.us/GNPS/SHS/dept/science/gaon/tab_3/documents/Test11handouts.pdf

http://mmsphyschem.com/lechatP.pdf

This worksheet contains multiple choice questions:

https://www.kent.edu/si/chem/upload/10060-004/worskeet_lechateliers_prin2.pdf

The National Science Teacher Association (NSTA ) annual conference is this week in Boston, Massachusetts.  For more information go to:

http://www.nsta.org/conferences/national.aspx

If you're attending the convention, please write me about it!

*I'd love to hear from you!  Your feedback would really help me to focus on your needs. You might be having a school vacation soon (spring breaks are around this time) -- take advantage of the time and write me about your classroom experiences!  There should be a "Contact" form below, or click on the "Contact" tab on the top right of this page.  

Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget

Each lab is presented with two possible report formats -- each lab uses the same procedure page but each has a different conclusion page -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required.  This gives the teacher the option of what type of report is desired! 

Have a good end of the week!


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    Marjorie R. Heesemann is a chemistry teacher with 15 years of experience who is now working to develop resources for the Chemistry classroom.

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