Chapter 19Chapter 19Acids and BasesAcids and Bases

Properties of AcidsProperties of Acids Taste sour (don’t try this at Taste sour (don’t try this at

home).home). Conduct electricity.Conduct electricity.

–Some are strong, others are weak electrolytes.

Properties of AcidsProperties of Acids React with metals to form React with metals to form

hydrogen gas.hydrogen gas. Change indicators (blue Change indicators (blue

litmus to red).litmus to red). React with hydroxides to React with hydroxides to

form water and a salt.form water and a salt.

Properties of BasesProperties of Bases

React with acids to form water React with acids to form water and a salt.and a salt.

Taste bitter.Taste bitter. Feel slippery (don’t try this Feel slippery (don’t try this

either).either).

Names and Formulas of AcidsNames and Formulas of Acids An acid is a chemical that An acid is a chemical that

produces hydrogen ions produces hydrogen ions (H(H1+1+) when dissolved ) when dissolved in in waterwater

Thus, general formula = HX, Thus, general formula = HX, where X is a monatomic or where X is a monatomic or polyatomic anionpolyatomic anion

Names and Formulas of AcidsNames and Formulas of Acids

HClHCl(g)(g) named hydrogen named hydrogen chloridechloride

HClHCl(aq)(aq) is named as an acid is named as an acid Name focuses on the Name focuses on the

anion presentanion present

Names and Formulas of AcidsNames and Formulas of Acids

1. When anion ends with -1. When anion ends with -ide, the acid starts with ide, the acid starts with hydro-,hydro-, and the stem of and the stem of the anion has the suffix the anion has the suffix --icic followed by the word followed by the word acidacid

Names and Formulas of AcidsNames and Formulas of Acids2. When anion ends with -ite, 2. When anion ends with -ite, the anion has the suffix the anion has the suffix -ous-ous, , then then acidacid

3. When anion ends with -ate, 3. When anion ends with -ate, the anion suffix is the anion suffix is -ic-ic and then and then acidacid

Table 19.1, page 588 for Table 19.1, page 588 for examplesexamples

Names and Formulas of BasesNames and Formulas of Bases A base produces A base produces

hydroxide ions (OHhydroxide ions (OH1-1-) ) when dissolved when dissolved in waterin water..

Named the same way as Named the same way as any other ionic compoundany other ionic compound–name the cation, followed by

anion

Names and Formulas of BasesNames and Formulas of Bases To write the formula: To write the formula:

write symbols; write write symbols; write charges; then cross (if charges; then cross (if needed)needed)

Hydrogen Ions from WaterHydrogen Ions from Water Water ionizes, or falls apart Water ionizes, or falls apart

into ions:into ions:H2O H1+ + OH1-

Called the “self ionization” of Called the “self ionization” of waterwater

Occurs to a very small extent:Occurs to a very small extent:[H1+ ] = [OH1-] = 1 x 10-7 M

Hydrogen Ions from WaterHydrogen Ions from Water Since they are equal, a Since they are equal, a

neutralneutral solution results solution results from waterfrom water

KKww = [H = [H1+1+ ] x [OH ] x [OH1-1-] = 1 x ] = 1 x 1010-14-14 M M22

KKww is called the is called the “ion product constant”“ion product constant”

Ion Product ConstantIon Product Constant HH22O O H H++ + OH + OH--

KKww is constant in every is constant in every aqueous solution: aqueous solution: [H [H++] x [OH] x [OH--] = 1 x ] = 1 x 1010-14 -14 MM22

If [HIf [H++] > 10] > 10-7-7 then [OH then [OH--] < 10] < 10-7-7 If [HIf [H++] < 10] < 10-7-7 then [OH then [OH--] > 10] > 10-7-7

Ion Product ConstantIon Product Constant If we know one, other can be If we know one, other can be

determineddetermined If [HIf [H++] > 10] > 10-7 -7 , ,

it is it is acidicacidic and and [OH[OH--] < 10] < 10-7-7

If [HIf [H++] < 10] < 10-7 -7 , , it is it is basicbasic and [OH and [OH--] > ] > 1010-7-7

Basic solutions also called Basic solutions also called “alkaline”“alkaline”

ExampleExample

[H+] = 1 x 10[H+] = 1 x 10-5-5 M M

Acid, Base Acid, Base or Neutralor Neutral

1010-5-5 > 10 > 10-7-7

AcidicAcidic

The pH conceptThe pH concept Logarithms are powers of Logarithms are powers of

ten.ten. definition: definition:

pH = pH = -log[H-log[H++]] in neutral in neutral

pH = pH = -log(1 x 10-log(1 x 10-7-7) = 7) = 7 in acidic solution [Hin acidic solution [H++] > 10] > 10-7 -7

in basic solution [Hin basic solution [H++] < 10] < 10-7 -7

The pH conceptThe pH concept pH pH < -log(10< -log(10-7-7)) pH < 7 pH < 7

(0 to 7 is the (0 to 7 is the acidacid range)range)

in base, pH > 7 in base, pH > 7 (7 to 14 is (7 to 14 is base base range)range)

pH and pOHpH and pOH pOH = -log [OHpOH = -log [OH--] ] [H[H++] x [OH] x [OH--] = 1 x 10] = 1 x 10-14 -14 MM22

pH + pOH = 14pH + pOH = 14 Thus, a solution with a pOH Thus, a solution with a pOH

less than 7 is basic; with a less than 7 is basic; with a pOH greater than 7 is an pOH greater than 7 is an acidacid

0 1 3 5 7 9 11

13

140135791

113

14

Basic

100

10-

1

10-

3

10-

5

10-

7

10-

9

10-

11

10-

13

10-

14

Basic

100

10-

1

10-

3

10-

5

10-

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10-

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10-

11

10-

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10-

14

Acidic Neutral

[OH-]

pH

[H+]

pOH

What is the pH of a solution with H–What is the pH of a solution with H–ion concentration of 4.2 X 10ion concentration of 4.2 X 10-10-10M.M.

pH = -log [H+]pH = -log [H+]pH = -log (4.2 X 10pH = -log (4.2 X 10-10-10))

pH = -(log 4.2 + log 10pH = -(log 4.2 + log 10-10-10]]

pH = -(0.645 + (-10))pH = -(0.645 + (-10))

pH = -(0.645 + (-10))pH = -(0.645 + (-10))

pH = 9.38 AlkalinepH = 9.38 Alkaline

pH is 6.35, what is the H–ion pH is 6.35, what is the H–ion concentration?concentration?

pH = -log [H+]pH = -log [H+]-log [H+] = 6.34-log [H+] = 6.34

log [H+] = -6.34log [H+] = -6.34

[H+] = 10 [H+] = 10 -6.34-6.34

[H+] = 4.5 X 10[H+] = 4.5 X 10-7-7 M M

Measuring pHMeasuring pH Why measure pH?Why measure pH?

–Everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.

Sometimes we can use Sometimes we can use indicators, other times we indicators, other times we might need a pH metermight need a pH meter

Acid-Base IndicatorsAcid-Base Indicators An indicator is an acid or base An indicator is an acid or base

that undergoes dissociation in that undergoes dissociation in a known pH range, and has a known pH range, and has different colors in solution different colors in solution (more later in chapter)(more later in chapter)

Examples: litmus, Examples: litmus, phenolphthalein, bromthymol phenolphthalein, bromthymol blue: Fig 20.8, p.590blue: Fig 20.8, p.590

Acid-Base IndicatorsAcid-Base Indicators A A pH meterpH meter may give more may give more

definitive resultsdefinitive results–some are large, others portable

–works by measuring the voltage between two electrodes

–needs to be calibrated