Wednesday, July 18, 2012

Activity Seven: Acids and Bases


Concept Questions on pH Scale 

by Trish Loeblein


1. The Color of a solution identifies if it is an acid, base, or neutral solution.
    a. True  b. False.  c. Pink are base and clear are acid.
   Litmus changes the color of the solution.

2. Which solution is basic?
      a. (clear)  b. (red)  c. (green)  d. more than one  e. none

3. Which solution is acidic?
     A.  B.  C.  D. More than one  E. Difficult to tell

4. Which solution is basic?
    A.  B.  C.  D. More than one  e. None

5.  Which solution is more acidic?
     A.  B.  C.  D. More than one  e. None

6.  How will adding water effect the pH?
        A. Increase the pH  B. Decrease the pH  C. No pH change
     The more water that is added, the less acid there will be causeing the pH to go up

7.  How will equal amount of water effect the pH?
       A. Increase the pH  B. Decrease the pH  C. The pH will be cut in half.  D. No pH change
    The more water will lessen the basicity causing the pH to go down.

 8.  What is the order from most acidic to most basic?
         A. abc  B. acb  C. bac  D. cba  E. cab   

9.  What is the order from most acidic to most basic?
        A. abc  B. acb  C. bac  D. cba  E. cab

10.  If spit has a pH = 7.4, what does that tell you about the water equilibrium?
         A. Something was added that made the equilibrium shift left
         B. Something was added that made the equilibrium shift right
         C. pH has nothing to do with the water equilibrium





Intro to Strong & Weak Acids and Bases

by Chris Bires


 
Procedure: 
·         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 - Red
 
5 - Orange-ish
12 - Blue
9 - Dark Green
7 - Yellow

Conductivity
(bright/dim/none
Bright
Dim
 Bright
Dim
Dim
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
(Strong) 
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
Strong
.100 M
Negligible
 1.00 x 10^-1
1.00 x 10^-1
1.00
Strong
1.00 M
Negligible
  1.00 x 10^0
 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
1/3
.015 M
 1.50 x 10^-2
3.87 x 10^-5
 3.87 x 10^-5
 4.41
1/3
.150 M
 1.50 x 10^-1
1.22 x 10^-4
 1.22 x 10^-4
3.91
4/5
.015 M
7.86 x 10^-5
 1.49 x 10^-2
1.49 x 10^-2
 1.83
4/5
.150 M
7.20 x 10^-3
1.43 x 10^-1
1.43 x 10^-1
0.85
Strong Bases
Strength
Initial Acid Concentration (mol/L)
[MOH] (mol/L)
[M+] (mol/L)
[OH-] (mol/L)
pH
Strong
.010 M
 Negligible
 1.00 x 10 ^-2
1.00 x 10 ^-2
12.00
Strong
.050 M
Negligible
5.00 x 10^-2
 5.00 x 10^-2
12.70
Strong
.100 M
Negligible
1.00 x 10^-1
1.00 x 10^-1 
 13.00
Strong
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
1/3
.015 M
1.50 x 10^-2
3.87 x 10^-5
3.87 x 10^-5
9.59
1/3
.150 M
 1.50 x 10^-1
 1.22 x 10^-4
 1.22 x 10^-4
10.09
4/5
.015 M
7.86 x 10^-5
1.49 x 10^-2
1.49 x 10^-2 
 12.17
4/5
.150 M
7.20 x 10^-3
1.43 x 10^-1 
1.43 x 10^-1
13.15

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.

There are more ions in the stronger acid, causing the pH level to be lower then it is in the weak acid. 











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