Water is everywhere! So, lets spend one more activity learning about one of the key aspects of water. Water has the ability to dissociate (break apart from HOH (or H2O) into H+ ions and OH- ions). We refer to solutions with lots of H+ ions as acids and solutions with lots of OH- ions as bases. By adding chemicals with H+ ions acidic solutions can be made. By adding chemicals with OH- ions basic solutions can be made.
Activity Tasks:
1. Review the Content Slides Acids and Bases on the D2L site.
2. Complete the Teaching Idea “Concept Questions for Chemistry using PhET” posted by Trish Loeblein on the pH Scale simulation at PHET (http://phet.colorado.edu/en/simulation/ph-scale). On your blog post the answers with your scientific explanations from the “Clicker Questions pH Scale” posted by Trish.
1. B. False. The color of something can’t show what it is. You can always color stuff by using dye.
2. D. More than one. This would include B and C because they have a pH around 7 and 8.
3. C. I believe it is C because this solution looks like it has more molecules in it although it is difficult to tell.
4. B. This is because there is more of the OH- solution than the H3O+.
5. D. More than one. This is because A and B both have a large amount of H3O+.
6. A. Increase the pH. This is because when you add water, the acidity decreases.
7. B. Decrease the pH. This is because when you add water, the basicity is decreased and the pH goes down.
8. A. ABC. This is because you go up from 6.5 to 7.4 to 12.06.
9. C. BAC. This is because of the levels of H3O+ and the levels of OH-.
10. A. Something was added that made the equilibrium shift left. This is because the pH is more than 7.
3. Complete the Teaching Idea “Intro to Strong and Weak Acids and Bases” posted by Chris Bires on the Acid-Base Solutions simulation (http://phet.colorado.edu/en/simulation/acid-base-solutions) and post on your blog your data and answers to the questions posed.
Introduction to Strong and Weak Acids and Bases PhET Lab (rvsd 5/2011)
Introduction:
Notation:
Strong Bases are abbreviated MOH, with the OH representing the hydroxide ion (OH-) the base donates to the solution. The M is cation (M+) that is left in solution as the hydroxide is donated. .
Autoionization:
Procedure: PhET Simulations à Play With Sims à Chemistryà Acid-Base Solutions à
The concentration of the acids and bases used in the at 0.010 (10-2) Molar.
· Begin with a strong acid and lower the pH probe into the beaker. What is the pH of this solution?
· Test this strong acid with both pH paper and the conductivity probe. What color does the pH indicator become? Is this strong acid an electrolyte? Does current travel through this solution?
· Repeat the above tests with the weak acid, the strong base, and the weak base, and water. Collect your observations in the table below:
| | Strong Acid | Weak Acid | Strong Base | Weak Base | Water |
| pH meter read (value) | 2.00 | 4.50 | 12.00 | 9.50 | 7.00 |
| pH paper (color) | 2 | 5 | 12 | 9 | 7 |
| Conductivity (bright/dim/none) | Bright | Dim | Bright | Dim | None |
| Exists as Mostly (ions/molecules) | Molecules | Ions | Molecules | Ions | Molecules |
Procedure:
This simulation allows you to change the concentration of a strong and weak acid and base.
Complete the table below for some strong acids and bases and weak acids and bases by adjusting the concentration.
Strong Acids
| Strength | Initial Acid Concentration (mol/L) | [HA] (mol/L) | [A-] (mol/L) | [H+] (mol/L) | pH |
| | .010 M | Negligible | 1.00 x 10-2 | 1.00 x 10-2 | 2.00 |
| | .050 M | Negligible | 5.00 x 10-2 | 5.00 x 10-2 | 1.30 |
| | .100 M | Negligible | 1.00 x 10-1 | 1.00 x 10-1 | 1.00 |
| | 1.00 M | Negligible | 1.00 x 100 | 1.00 x 100 | 0.00 |
Weak Acids
| Strength (approximately) | Initial Acid Concentration (mol/L) | [HA] (mol/L) | [A-] (mol/L) | [H+] (mol/L) | pH |
| | .015 M | 1.50 x 10-2 | 3.19 x 10-5 | 3.19 x 10-5 | 4.50 |
| | .150 M | 1.50 x 10-1 | 1.01 x 10-4 | 1.01 x 10-4 | 4.00 |
| | .015 M | 4.75 x 10-4 | 1.45 x 10-2 | 1.45 x 10-2 | 1.84 |
| | .150 M | 3.16 x 10-2 | 1.18 x 10-1 | 1.18 x 10-1 | .93 |
Strong Bases
| Strength | Initial Acid Concentration (mol/L) | [MOH] (mol/L) | [M+] (mol/L) | [OH-] (mol/L) | pH |
| | .010 M | Negligible | 1.00 x 10-2 | 1.00 x 10-2 | 12.00 |
| | .050 M | Negligible | 5.00 x 10-2 | 5.00 x 10-2 | 12.70 |
| | .100 M | Negligible | 1.00 x 10-1 | 1.00 x 10-1 | 13.00 |
| | 1.00 M | Negligible | 1.00 x 100 | 1.00 x 100 | 14.00 |
Weak Bases
| Strength (approximately) | Initial Acid Concentration (mol/L) | [B] (mol/L) | [BH+] (mol/L) | [OH-] (mol/L) | pH |
| | .015 M | 1.50 x 10-2 | 1.37 x 10-5 | 1.37 x 10-5 | 9.14 |
| | .150 M | 1.50 x 10-1 | 4.34 x 10-5 | 4.34 x 10-5 | 9.64 |
| | .015 M | 2.80 x 10-4 | 1.47 x 10-2 | 1.47 x 10-2 | 12.17 |
| | .150 M | 2.14 x 10-2 | 1.29 x 10-1 | 1.29 x 10-1 | 13.11 |
Conclusion Questions:
1. A strong acid is very concentrated / exists primarily as ions.
2. A weak base is a nonelectrolyte / weak electrolyte / strong electrolyte.
3. A strong base is a nonelectrolyte / weak electrolyte / strong electrolyte.
4. At the same concentration (Molarity) a strong acid will have a higher / lower / the same pH as a weak acid.
5. As concentration of a weak acid increases, the pH increases / decreases / remains constant.
6. As concentration of a weak base increases, the pH increases / decreases / remains constant.
7. As the concentration of a weak acid increases, the number of ions increases / decreases / remains constant.
8. As the concentration of a weak acid increases, conductivity increases / decreases / remains constant.
9. As the strength of a weak acid increases, the proportion of ions to molecules increases / decreases.
10. As the strength of a weak acid increases, the conductivity increases / decreases / remains constant.
11. What are the pH values of a weak acid with a concentration of 0.10 and a strong acid with a concentration of 0.01, ten times lower?
Weak acid, 0.10 M = 4.0
Strong Acid, 0.01 M = 4.50
12. Explain the significance of the results of your calculation above. The pH value goes up by .5 every time you move over one decimal place to the left.
omg thank you some much
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