c. johannesson ch. 18- acids & bases ii. ph. c. johannesson a. ionization of water h 2 o + h 2 o...
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C. Johannesson A. Ionization of Water Find the hydroxide ion concentration of 3.0 M HCl. [H 3 O + ][OH - ] = 1.0 [3.0 ][OH - ] = 1.0 [OH - ] = 3.3 M Acidic or basic? AcidicTRANSCRIPT
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C. Johannesson
Ch. 18- Acids & Bases
II. pH
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C. Johannesson
A. Ionization of Water
H2O + H2O H3O+ + OH-
Kw = [H3O+][OH-] = 1.0 10-14
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C. Johannesson
A. Ionization of Water
Find the hydroxide ion concentration of 3.0 10-2 M HCl.
[H3O+][OH-] = 1.0 10-14
[3.0 10-2][OH-] = 1.0 10-14
[OH-] = 3.3 10-13 M
Acidic or basic?Acidic
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C. Johannesson
pH = -log[H3O+]
B. pH Scale
0
7INCREASING
ACIDITY NEUTRALINCREASING
BASICITY
14
pouvoir hydrogène (Fr.)“hydrogen power”
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C. Johannesson
B. pH Scale
pH of Common SubstancespH of Common Substances
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C. Johannesson
B. pH Scale
pH = -log[H3O+]
pOH = -log[OH-]
pH + pOH = 14
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C. Johannesson
B. pH Scale
What is the pH of 0.050 M HNO3?
pH = -log[H3O+]
pH = -log[0.050]
pH = 1.3
Acidic or basic?Acidic
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C. Johannesson
B. pH Scale
What is the molarity of HBr in a solution that has a pOH of 9.6?
pH + pOH = 14
pH + 9.6 = 14
pH = 4.4
Acidic
pH = -log[H3O+]
4.4 = -log[H3O+]
-4.4 = log[H3O+]
[H3O+] = 4.0 10-5 M HBr
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C. Acid-Base Indicators Why measure pH?
Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.
Sometimes we can use indicators, other times we might need a pH meter
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Acids Affect Indicators, by changing their color
Blue litmus paper turns red in contact with an acid (and red paper stays red).
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Bases Affect Indicators
Red litmus paper turns blue in contact with a base (and blue paper stays blue).
Phenolphthalein turns purple in a base.
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How to measure pH with wide-range paper
1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod.
2.Compare the color to the chart on the vial – then read the pH value.
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Some of the many pH
Indicators and theirpH range
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C. Acid-Base IndicatorsAlthough useful, there are limitations
to indicators:• usually given for a certain
temperature (25 oC), thus may change at different temperatures
• what if the solution already has a color, like paint?
• the ability of the human eye to distinguish colors is limited
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C. Acid-Base IndicatorsA pH meter may give more definitive
results• some are large, others portable• works by measuring the voltage
between two electrodes; typically accurate to within 0.01 pH unit of the true pH
• Instruments need to be calibrated
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Worksheet and bookwork
Complete worksheet 18.3Bookwork p. 651 problem 22p. 653 24, 25p. 654 27
C. Johannesson