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

Litmus paper changes from

Acid Neutral Base

Blue to Red

Does not Change

Red to Blue

Source: 2003 VA EOC Exam

pHAcids and

Bases

A Quick Reminder…• Reactions can stop at an EQUILIBRIUM

Image source: http://cwx.prenhall.comNO2 + NO2 N2O4

The Equilibrium Constant, Keq

[C]c [D]d

[A]a [B]b

For the reaction:

aA + bB cC + dDWhere:

• a, b, c, d are coefficients

• A, B, C, D are substances

(products)

(reactants)[ ] = concentration in M

Keq =

The Equilibrium Constant, Keq

For the reaction:

NO2 + NO2 N2O4

Keq =[N2O4]1

[NO2]1 [NO2]1

Keq =[N2O4]1

[NO2]2

2 NO2 N2O4

=[N2O4][NO2]2

=[N2O4][NO2]2

A Special Equilibrium Constant, Kw

For the reaction:

H2O + H2O H3O+ + OH-

Kw =[H3O+] [OH-]

[H2O]2= [H3O+] [OH-]

Kw = [1.00 x 10-7] [1.00 x 10-7] = 1.00 x 10-14

“hydronium” “hydroxide”

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

Practice ProblemsUsing 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 10-5 M= 1 x 10-9 M

Practice Problems2. 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

0.0010 M= 1 x 10-11 M

Practice Problems3. 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?

0.080 g NaOH x 1 mol NaOH

40.00 g NaOHx 1 mol OH-

1 mol NaOH= 0.0020 mol OH-

[OH-] = 0.0020 mol OH-

2.0 L

= 0.0010 M OH-

0.0010 M OH-

Kw = [H3O+] [OH-]

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

[H3O+] = 1.00 x 10-14

0.0010 M= 1.0 x 10-11 M H3O+

1.0 x 10-11 M H3O+

Practice Problems4. 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?

0.080 g Ca(OH)2 x 1 mol Ca(OH)2

74.10 g Ca(OH)2

x 2 mol OH-

1 mol Ca(OH)2

= 0.00216 mol OH-

[OH-] = 0.00216 mol OH-

2.0 L

= 0.00108 M OH-

Kw = [H3O+] [OH-]

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

[H3O+] = 1.00 x 10-14

0.00108 M= 9.3 x 10-12 M H3O+

0.0020 M OH-

9.3 x 10-12 M H3O+

pH – the POWER of H+!

These numbers represent the POWER of H+

pH = the negative logarithm of [H3O+]Image source: http://www.lowimpactdevelopment.org

Log-o-rhythms

= =

pH = the negative logarithm of [H3O+]POWERpH – the POWER of H+!

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

pH = - log [H3O+]

My Kingdom for a Calculator!

On TI-83:

• push “(-)” key

• push “log” key

• type in number

On Scientific Calculators:

• type in number

• push “log” key

• push +/- key

To solve for pH, given hydronium molarity

Practice Problems1. 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.

Practice Problems2. 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?

pH = - log [H3O+]

pH = - log (1.0 x 10-10)

pH = 10.00 BASIC

Kw = [H3O+] [OH-]

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

[H3O+] = 1.00 x 10-14

1.0 x 10-4 M= 1 x 10-10 M

My Kingdom for a Calculator (again)!

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

To solve for hydronium molarity, given pH

Practice Problems3. 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

Practice Problems4. 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

1.0 x 10-8 M= 1 x 10-6 M

Practice Problems5. 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?

5.33 g HCl x 1 mol HCl

36.46 g HClx 1 mol H+

1 mol HCl= 0.146 mol H+

[H+] = 0.146 mol H+

2.50 L

= 0.0584 M H+

pH = - log [H3O+]

pH = - log (0.0584)

pH = 1.234

Homework

• Complete the practice problems on the worksheet. Due next class