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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
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