Activity 7

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. False. The color of the solution does not signify if it is a acid or base. It is the color of the Ph scale that signifiys if it is an acid, base, or neutral.

2. D More than one. It would be both B and C because both of their PH's are over 7.0 so they could both be considered basic.

3. C. There is more H30 in the solution and very little OH. OH is more basic and H3O is more acidic.

4. B. There is much more OH than H30. The OH is Basic so it overcomes the H30 since there is more of it.

5. D. I believe there would be more than one. Both A and B would be acidic because there is more H30 than there is OH in these.

6. A. Increase the PH. The water lessens the acid which makes the PH go up.

7. B. More water will decrease the PH because it decreases the basicity

8. A. The lower the PH the more acidic it is. The higher the PH the more basic it is.

9. E. The more OH a substance has the more basic it is, The more H3O a substance has the more acidic it is. When the OH and H3O are equal they are neutral.

10. A. it had to shift left because the pH went up from 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.

Name:____________________

Introduction to Strong and Weak Acids and Bases PhET Lab (rvsd 5/2011)

        How does the strength of an acid or base affect conductivity?pH?

Introduction:

When you test your pool’s pH, what are you those little vials or paper strips telling you?  When you hear an acid called “strong” or “weak”, what do those terms refer to?  In aqueous solutions, compounds can exist as molecules (undissociated) or ions (dissociated).  When an acid or a base exists in solution nearly completely as dissociated ions, we refer to that acid or base as strong.  A weak acid or base will donate ions to the solution, but will remain primarily as undissociated molecules.

Notation:

Acids are abbreviated HA, with the H representing the proton (H+) the acid donates to the solution.  The A is referred to as the acidic anion (A-) that is left in solution as the proton is donated.

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:

Even without any acid or base added a very small number of water molecules will form protons (H+) and hydroxide ions (OH-).  The protons will then form hydronium ions, the acid ion.

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)	2.0	4.50	12	9.50	7.0
pH paper (color)	Pink or #2	Orange 4	12 teal	9 green	7 orange
Conductivity (bright/dim/none)	Bright	dim	bright	dim	Very dim
Exists as Mostly (ions/molecules)	Ions	Molecules	Ions	molecule	molecule

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	negligable	55.6	1.00 X 10^-2	2.00
	.050 M	negligable	55.6	5.00 X 10^-2	1.30
	.100 M	negligable	55.5	1.00 X 10^-1	1.00
	1.00 M	negligable	54.6	1.00 X 10^0	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	55.6	3.87 X 10^ -5	4.41
	.150 M	1.50 X 10^-1	55.6	1.22 X 10^-4	3.91
	.015 M	1.36 X 10^ -4	55.6	1.49 X 10^-2	1.83
	.150 M	1.17 X 10^-2	55.5	1.38 X 10^-1	0.89

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	1.00X10^-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 10^0	1.00 X 10^0	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	4.20 X 10^-5	4.20 X 10^-5	9.62
	.150 M	1.50 X 10^ -1	1.33 X 10^-4	1.33 X 10^-4	10.12
	.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. (circle)

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 :____4.00________         Strong Acid, 0.01 M :____2.00________

12.  Explain the significance of the results of your calculation above. ___I was surprised to find that the Ph value is higher in weak acid than in strong acid. I was expecting it to be the other way around but because of the ion concentration it creates this. _______________________________