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Chapter 16 Equilibrium in Acid-Base Systems

Section 16.1   Water Ionization and Acid - Base Strength

Web Activity: Canadian Achievers ¾ Edgar Steacie (page 53)

Edgar Steacie was an internationally acclaimed research scientist and a senior administrator of the National Research Council.

1. What was Steacie's main area of research?

2. Why was Steacie known as a statesman of science for Canada ?

3. What is a Steacie Fellowship?

Science.ca

This short profile of Steacie gives a brief outline of his achievements.

The Canadian Encyclopedia

Steacie's professional life was clearly influenced by some illustrious colleagues.

The Steacie Fellowship

Up to six Steacie Fellowships are awarded each year. This NSERC site gives information about the type of candidates who are awarded the fellowship as well as the dollar value. There is also a link on this site to another Steacie award: The Steacie Prize for Natural Sciences.

Science and Engineering Research Canada ¾ Call for Nominations

Winning a Steacie Fellowship is not a simple process. This NSERC site gives you an idea of the long, involved process through which nominators and nominees have to go.

Section 16.2   The Br ø nsted - Lowry Acid - Base Concept

Career Connection: Chemical Researcher (page 60)

Farideh Jalilehva is an associate professor of chemistry at the University of Calgary . Her research involves a lot of X-ray absorption spectroscopy. Find out how acidity due to sulfur in plant tissues is connected to ancient shipwrecks by visiting her information site, and check out her curriculum vitae (CV). Science is international in scope!

Dr. Farideh Jalilehvand

Dr. Jalilehvand's Web page describes her work at the University of Calgary 's Chemistry Department, and outlines her CV.

Section 16.4   Interpreting pH Curves

Web Activity: Titration Simulation (page 94)

SIR Titrate is a simulation that lets you set up titrations and observe endpoints. You can use this simulation to explore and examine titrations involving weak acids or bases, and also sequential reaction titrations involving diprotic entities.

[Use SIR Titrate - see SIRs CD-ROM]

Purpose

The purpose of this simulation is to investigate pH curves for the titration of a weak acid, weak base and polyprotic substance.

Simulation Procedure

.  In the Acid-Base Equilibrium section, click on SIR Titrate to start the program and read the general description ("analyte" means the sample solution). Click anywhere to go to the main screen.

Part 1 - Weak Acid Titration

1. Follow the instructions to set K 1 = 6.3 ´ 10 -5 . This will select benzoic acid as the weak acid to be titrated with a strong base. Do not alter any other variables.
2. Click the point of the pH curve corresponding to the endpoint pH. Adjust the crosshairs, if necessary, to fine-tune the position. Record the endpoint pH and the equivalence point volume.
3. Click Choose Indicator button. Using a trial-and-error method, choose the best indicator whose colour change range best overlaps with the endpoint pH. Record the indicator chosen.
4. Click Titration button. After the burette is filled with the titrant (strong base), lower the liquid level so that it is on the scale, just below 0.0 mL.
5. Click Read Burette button. Use the calculator on the screen to enter the initial burette reading. Record this volume.  
6. The next screen shows the burette with the measured volume of the sample and your chosen indicator in the simulated flask.
7. Use the controls to add the titrant to the sample. Note how the graph shows the progress of the reaction as an instantaneous pH of the mixture. Add titrant more quickly in the early stages and slowly (dropwise) when you are near the vertical portion of the pH curve.  
8. You should aim to stop the titration when one drop of titrant changes the colour of the indicator in the sample.
9. Click Read Burette button and enter the final burette reading. Record this reading and calculate the volume of titrant added to the flask.
10. The next screen tells you how close you came to the predicted equivalence point.  
11. Click Start Over button.

    Part 2 - Weak Acid and Base pH Curves

12. Click Try an Unknown button on the lower right corner of the screen.
13. In the menu on the left, click Monofunctional Weak Acid and notice the pH curve that appears.
14. Each time you click Monofunctional Weak Acid , you get a slightly different weak acid and its pH curve. Do this several times and notice the orientation of the curve and approximate endpoint pH. Write a general statement to describe the pH curve and the endpoint pH for the titration of weak acids.
15. Repeat steps 14 and 15 using Monofunctional Weak Base.

    Part 3 -Polyprotic pH Curves

16. Repeat steps 14 to 16 using Difunctional Weak Acid .
17. Repeat steps 14 to 16 using Difunctional Weak Base .

Biology Connection: Homeostasis (page 97)

Many reactions in the human body can produce or consume carbonic acid or hydrogen carbonate ions. When one of these entities is depleted in the blood, Le Chatelier's principle comes into effect, and more of that entity is produced by an equilibrium shift to keep everything in balance. There are countless equilibrium reactions interconnected in this way in all solutions in and around living cells. Biologists refer to this interdependent network of reaction equilibria as an example of homeostasis-the condition of automatic continual readjustment of cells, systems, and whole organisms to optimum (and usually very specific) conditions. Biology courses will tell you a lot more about homeostasis and the factors that affect it.

How Stuff Works: Homeostasis

Through a short animation clip, How Stuff Works compares homeostasis to a thermostat and provides an example of homeostasis: how the endocrine system controls sugar levels.

Wikpedia: Homeostasis

This page from Wikpedia provides a general definition of homeostasis, its properties and mechanisms of feedback, and the difference between biological homeostasis and ecological homeostasis.

Biology-Online: Physiological Homeostasis

[Link to pdf pages from Nelson Biology Alberta 20-30 - to come]

Web Activity: Buffer Systems (page 97)

This SIR Buffer simulation allows the construction of selected buffer system equilibria and illustrates the buffering ability by comparing the buffer's titration pH curve to that of a strong acid or strong base.

[Use SIR Buffer -- see SIRs CD-ROM]

In this simulation you will construct a buffer system and test its buffering ability compared to that of a non-buffered solution with the same initial pH.

1. Start the SIRs program and on menu screen, click on "SIR Buffer."
2. Read the general instructions and click anywhere to proceed.
3. Choose acetic acid as the weak acid and acetate ion as the (conjugate) base.
4. Click the "Make up solutions" box.
5. Under the acetic acid formula, set the initial amount concentration to 0.100 mol/L by clicking on the white box and using the pop-up calculator. Notice that the program automatically calculates the pH of this acetic acid solution.
6. Under the acetate ion formula; set the initial amount concentration to 0.100 mol/L. The calculated pH now changes to represent the pH of a buffer system containing equal amounts of acetic acid and acetate ion.
7. Click the "Titrate and Plot" box.
8. The buffer solution you have prepared appears at the junction of the red and blue lines. The red line represents what happens to the pH of the buffer when a strong acid is added; the blue line is for the addition of a strong base to the buffer.
9. Click the on the line and adjust if necessary to fine-tune the crosshairs to the starting buffer; i.e., volume of titrant = 0 mL and pH = 4.70.
10. Click on the "Equivalent HCl solution" box. This new curve represents the addition of a strong acid or strong base to a dilute HCl solution whose initial pH (at volume = 0 mL) is the same as the buffer solution (4.70).
11. Suppose you were to add 1 mL of a strong acid to your buffer. Click the cursor on the buffer line and fine tune the crosshairs to obtain the pH of the buffer for a volume of acid added equal to 1.00 mL.
12. Record the pH and calculate the change in pH of the buffer.
13. Click the cursor on the equivalent HCl curve and fine tune the crosshairs so that the volume of extra acid added is also 1.00 mL.
14. Record the pH and calculate the change in pH of this non-buffered solution.
15. Compare the change in the pH of the buffer with the change in pH of the non-buffered solution of the same acidity.
16. Repeat steps 11 to 15 adding 1.00 mL of a strong base.
17. Click the "New Solution" box to return to the previous screen. Here you can change the initial concentrations of the buffer or click the "New System" box to return to the acid-base menu to choose a different buffer mixture.

Web Activity: Canadian Achievers ¾ Maud Menten (page 98)

Maud Menten was a world-renowned pioneer in explaining the chemical action of enzymes. What key concept was her chief contribution to understanding enzyme activity?

Maud Menten

This University of Toronto Web page describes Menten's many achievements.

Some Called Her Miss Menten

The University of Pittsburg 's online magazine, PittMed , looks at the very human side of Maud Menten. The article also presents the famous equation that bears her name.