Activity 7

  1.     The color of the solution identifies if it is an acid, base, or neutral solution?

Answer:  B. False

  2.    Which solution is basic?

Answer:  D. More than one, because any solution that has a pH balance above 7.0 is basic.

  3.    Which solution is acidic?

Answer:  C

  4.    Which solution is basic?

Answer:  B

  5.    Which solution is acidic?

Answer: D both A and B are acidic

  6.    How will adding water affect the pH?

Answer: A. adding more water increases the pH.

  7.    How will equal amount of water affect the pH?

Answer: B.  decreases the pH.

  8.    What is the order from most acidic to most basic?

Answer: A; ABC

  9.    What is the order from most acidic to most basic?

Answer: C; BAC

  10.  If spit has a pH= 7.4, what does that tell you about the water equilibrium?  2H2O  OH-  + H3O+

Answer: A. something was added that made the equilibrium shift left.

Name: Larissa Lewan

Introduction to Strong and Weak Acids and Bases PhETLab(rvsd5/2011)

        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 ChemistryàAcid-Base Solutionsà

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? The pH is 2.00.

·         Test this strong acid with both pH paper and the conductivity probe.  What color does the pH indicator become?With the pH paper is it a 2.  Is this strong acid an electrolyte? yes  Does current travel through this solution? Yes it does.

·         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)	Red	Orange	Blue	Green	Yellow
Conductivity (bright/dim/none)	Bright	Dim	Bright	Dim	Very dim
Exists as Mostly (ions/molecules)	Molecule	Molecules	Ions	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	9.84 x 10^-3	9.84 x 10^-3	2.01
	.050 M	Negligible	4.95 x 10^-2	4.95 x 10^-2	1.31
	.100 M	Negligible	1.00 x 10^-1	1.00 x 10^-1	1.00
	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
	.015 M	1.50 x 10^-2	2.39 x 10^-5	2.39 x 10^-5	4.38
	.150 M	1.50 x 10^-1	7.55 x 10^-1	7.55 x 10^-1	3.88
	.015 M	2.33 x 10^-4	1.48 x 10 ^-2	1.48 x 10 ^-2	1.83
	.150 M	1.85 x10^-2	1.32 x 10^-1	1.32 x 10^-1	.88

Strong Bases

Strength	Initial Acid Concentration (mol/L)	[MOH] (mol/L)	[M+] (mol/L)	[OH-] (mol/L)	pH
	.010 M	Negligible	9.84 x 10^-3	9.84 x 10^-3	11.99
	.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	7.90 x 10^-6	7.90 x 10^-6	8.90
	.150 M	1.50 x 10^-1	2.50 x 10^-5	2.50 x 10^-5	9.40
	.015 M	2.33 x 10-4	1.48 x 10^-2	1.48 x 10^-2	12.17
	.150 M	1.85 x 10 ^-2	1.32 x 10^-1	1.32 x 10^-1	13.13

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 ionsincreases / decreases / remains constant.

8.       As the concentration of a weak acid increases, conductivityincreases / decreases / remains constant.

9.       As the strength of a weak acid increases, the proportionof ions to moleculesincreases / decreases.

10.   As the strength of a weak acid increases, the conductivityincreases / 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      Strong Acid, 0.01 M   2    

12.   Explain the significance of the results of your calculation above. The strong acid is two times less then the weak acid.