Activity #7

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.

pH Scale Questions: 
1. B. False

(Explanation: the left is milk, then blood, then a custom liquid like NaOH)

2. D. More than one (Explanation: A. milk, B. blood, C. custom at pH =12)
3. C. (Explanation: A. Custom pH =13  B. water pH =7  C. vomit pH=2)
4. B.(Explanation: A. Water pH =7 B. pH =13  C. soda pop pH =2.5)
5. D. More than one (Explanation: A. Coffee pH =5, B. soda pop pH =2.5, C. custom pH =13)
6. A. increase the pH (Explanation: more water lessens the acidity, so pH goes up)
7. B. decrease the pH (Explanation: more water lessens the basicity , so pH goes down)
8. A. A B C (Explanation: Milk, blood, pH=12)
9. C. B A C (Explanation: 7 pH =13, Water pH =7, soda pop pH =2.5)
10. A. Something was added that made the equilibrium shift left (

Explanation: Since the pH is not 7, then something was added to make the equilibrium shift left. For example, if NaOH was added to water, OH- is immediately in the solution and some of it will react with the H3O+  , so the pH (which is inversely related to [H3O+ ]), goes up. 

If something like HCl were added there would be more H3O+ , which would also cause a shift left, but there would be less OH- , (which is directly related to pH), so the pH is less 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.

	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)	Red	Orange	Blue	Green	Yellow
Conductivity (bright/dim/none)	Bright	Dim	Bright	Dim	None
Exists as Mostly (ions/molecules)	Ions	Molecules	Ions	Molecules	Ions

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
	.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
	1.00 M	negligible	1.00 x 10^0	1.00 x 10^0	0

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	3.87 x 10^-5	3.87 x 10^-5	4.41
	.150 M	1.50 x 10^-1	1.22 x 10^-4	1.22 x 10^-4	3.91
	.015 M	1.36 x 10^-4	1.49 x 10^-2	1.49 x 10^-2	1.83
	.150 M	1.17 x 10^-2	1.28 x 10^-1	1.28 x 10^-1	0.86

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
	.050 M	negligible	5.00 x 10^-2	5.00 x 10^-2	12.7
	.100 M	negligible	1.00 X 10^-1	1.00 X 10^-1	13
	1.00 M	negligible	1.00 x 10^0	1.00 x 10^0	14

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	3.87 x 10^-5	3.87 x 10^-5	9.59
	.150 M	1.50 x 10^-1	1.22 x 10^-4	1.22 x 10^-4	10.09
	.015 M	1.36 x 10^-4	1.49 x 10^-2	1.49 x 10^-2	12.17
	.150 M	1.17 x 10^-2	1.38 x 10^-1	1.38 x 10^-1	13.14

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: 4.57         Strong Acid, 0.01 M :2

12.  Explain the significance of the results of your calculation above. The weak acid has a higher pH than the strong acid because there is less ions in the weak acid and  therefore has a larger pH.