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Bell Ringer. Which of the following aqueous solutions will cause litmus paper to turn red? A NaOH B NaCl C HCl D H 2 O. pH. 1-6. 7. 8-14. Solution Added. Acid. Neutral. Base. Litmus paper changes from. Blue to Red. Does not Change. Red to Blue. Source: 2003 VA EOC Exam.

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Bell Ringer

Which of the following aqueous solutions will cause litmus paper to turn red?

A NaOH

B NaCl

C HCl

D H2O

pH

1-6

7

8-14

Solution Added

Acid

Neutral

Base

Litmus paper changes from

Blue to Red

Does not Change

Red to Blue

Source: 2003 VA EOC Exam


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pH

Ms. Besal

4/14/2006


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A Quick Reminder…

  • Reactions can stop at an EQUILIBRIUM

NO2 + NO2 N2O4

Image source: http://cwx.prenhall.com


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aA + bBcC + dD

(products)

(reactants)

The Equilibrium Constant, Keq

For the reaction:

  • Where:

    • a, b, c, d are coefficients

    • A, B, C, D are substances

[C]c[D]d

Keq =

[A]a[B]b

[ ] = concentration in M


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NO2 + NO2 N2O4

2 NO2 N2O4

The Equilibrium Constant, Keq

For the reaction:

[N2O4]1

[N2O4]

Keq =

=

[NO2]1 [NO2]1

[NO2]2

[N2O4]1

[N2O4]

Keq =

=

[NO2]2

[NO2]2


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H2O + H2O H3O+ + OH-

A Special Equilibrium Constant, Kw

For the reaction:

[H3O+] [OH-]

[H3O+] [OH-]

=

Kw =

[H2O]2

“hydronium”

“hydroxide”

[1.00 x 10-7] [1.00 x 10-7]

= 1.00 x 10-14

Kw =

Image source: http://cwx.prenhall.com


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Practice Problems

Using the knowledge that Kw = 1.00 x 10-14, solve for the missing piece of information:

1. Calculate the hydroxide ion concentration in a solution whose hydronium ion concentration is 1 x 10-5 M

Kw = [H3O+] [OH-]

1.00 x 10-14 = [1 x 10-5 M] [OH-]

[OH-] = 1.00 x 10-14

=

1 x 10-9 M

1 x 10-5 M


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Practice Problems

2. Calculate the hydronium concentration for a solution whose hydroxide concentration is 0.0010 M.

Kw = [H3O+] [OH-]

1.00 x 10-14 = [H3O+] [0.0010 M]

[H3O+] = 1.00 x 10-14

=

1 x 10-11 M

0.0010M


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Practice Problems

3. What is the hydroxide concentration of a solution if 0.080 grams of NaOH are dissolved in 2.0 L of solution?

What is the hydronium ion concentration of this solution?

0.0010 M OH-

1.0 x 10-11 M H3O+

1 mol NaOH

1 mol OH-

0.080 g NaOH

0.0020 mol OH-

x

x

=

40.00 g NaOH

1 mol NaOH

[OH-] =

0.0020 mol OH-

=

0.0010 M OH-

2.0 L

Kw = [H3O+] [OH-]

1.00 x 10-14 = [H3O+] [0.0010 M]

[H3O+] = 1.00 x 10-14

=

1.0 x 10-11 M H3O+

0.0010M


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Practice Problems

4. What is the hydroxide ion concentration of a solution if 0.080 grams of Ca(OH)2 are dissolved in 2.0 L of solution?

What is the hydronium ion concentration of this solution?

0.0020 M OH-

9.3 x 10-12 M H3O+

1 mol Ca(OH)2

2 mol OH-

0.080 g Ca(OH)2

0.00216 mol OH-

x

x

=

74.10 g Ca(OH)2

1 mol Ca(OH)2

[OH-] =

0.00216 mol OH-

=

0.00108 M OH-

2.0 L

Kw = [H3O+] [OH-]

1.00 x 10-14 = [H3O+] [0.00108 M]

[H3O+] = 1.00 x 10-14

=

9.3 x 10-12 M H3O+

0.00108M


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pH – the POWER of H+!

These numbers represent the POWER of H+

pH = the negative logarithm of [H3O+]

Image source: http://www.lowimpactdevelopment.org


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Log-o-rhythms

Logarithm

Exponent

POWER

=

=

pH – the POWER of H+!

pH = the negative logarithm of [H3O+]

POWER

pH = - log [H3O+]

Answer the following questions without using a calculator:

  • What is the pH of a solution with [H3O+] = 1.0 x 10-4 M?

pH = 4.00

ACID

  • What is the pH of a solution with [H3O+] = 1.0 x 10-12 M?

pH = 12.00

BASE


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My Kingdom for a Calculator!

To solve for pH, given hydronium molarity

  • On TI-83:

  • push “(-)” key

  • push “log” key

  • type in number

  • On Scientific Calculators:

  • type in number

  • push “log” key

  • push +/- key


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Practice Problems

1. What is the pH of a solution if the concentration of hydronium ions is 1.0 x 10-2 M? Is the solution acidic or basic?

pH = - log [H3O+]

pH = - log (1.0 x 10-2)

pH = 2.00

ACIDIC

SIG FIG RULES: Put the correct number of Sig Figs BEHIND the decimal point.


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Practice Problems

2. What is the pH of a solution if the concentration of hydroxide ions is 1.0 x 10-4 M? Is the solution acidic or basic?

Kw = [H3O+] [OH-]

1.00 x 10-14 = [H3O+] [1.0 x 10-4 M]

[H3O+] = 1.00 x 10-14

=

1 x 10-10 M

1.0 x 10-4 M

pH = - log [H3O+]

pH = - log (1.0 x 10-10)

pH = 10.00

BASIC


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My Kingdom for a Calculator (again)!

To solve for hydronium molarity, given pH

  • On TI-83:

  • push “10x” key

  • push “(-)” key

  • type in pH

  • On Scientific Calculators:

  • type in number

  • push +/- key

  • push “2nd” key

  • push “log” key


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Practice Problems

3. What is the concentration of hydronium ions in a solution whose pH is 8.00?

pH = 8.00 = - log [H3O+]

-8.00 = log [H3O+]

10–8.00 M = [H3O+]

[H3O+] = 1.00 x 10-8 M


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Practice Problems

4. For Question #3, what is the concentration of hydroxide ions?

Kw = [H3O+] [OH-]

1.00 x 10-14 = [1.0 x 10-8 M] [OH-]

[OH-] = 1.00 x 10-14

=

1 x 10-6 M

1.0 x 10-8 M


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Practice Problems

5. What is the concentration of hydronium ions in a solution that has a volume of 2.50 L and 5.33 g of HCl? What is the pH of this solution?

1 mol HCl

1 mol H+

5.33 g HCl

0.146 mol H+

x

x

=

36.46 g HCl

1 mol HCl

[H+] =

0.146 mol H+

=

0.0584 M H+

2.50 L

pH = - log [H3O+]

pH = - log (0.0584)

pH = 1.234