1The Chemistry of Acids and Bases

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Some Properties of Acids

þ React with certain metals to produce hydrogen gas.

þ React with carbonates and bicarbonates to produce carbon dioxide gas

þ Taste sour

þ Corrode metals

þ Electrolytes

þ React with bases to form a salt and water

þ pH is less than 7

þ Turns blue litmus paper to red “Blue to Red”

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Some Properties of Bases

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

React with acids to form salts and water

pH greater than 7

Corrosive

Turns red litmus paper to blue “Basic Blue”

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Acid and Bases

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Acid and Bases

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Acid and Bases

7Indicators

• Indicators are dyes that can be added in small amounts that will change color in the presence of an acid or base.

• Some indicators only work in a specific range of pH

8Examples: Indicators

• Litmus paper• Phenolpthalein• Bromothymol blue• Methyl Orange

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Universal Indicator

• Universal indicator is a pH indicator composed of a blend of several compounds that changes colour over a wide range of pH values from 1-14 to indicate the strength of acidity or basicity (alkalinity) of a solution.

Cabbage juice

pH paper

11• A universal indicator is typically composed of water, methanol, proan-1-ol, phenolpthalein, sodium salt, methyl red, bromothylmol blue, monosodim salt and thymol blue monosodium salt.

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pH meter• When precise

measurement of pH required.

• Tests the voltage of the electrolyte

• Converts the voltage to pH

• Must be calibrated with a buffer solution

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pH of Common Substances

14The pH scale is a way of expressing

the strength of acids and bases.

Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+

(or OH-) ion.

pH = - log [H+](Remember that the [ ] mean

Molarity)

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The pH scale is a way of expressing the strength of acids and bases. Under 7 = acid

7 = neutral Over 7 = alkaline (base)

16pH is a logarithmic function

• pH 2 ____ more acidic than a pH of 3• pH 2 ____ more acidic than a pH of 4• pH 2 ____ more acidic than a pH of 5

pH = - log [H+](Remember that the [ ] mean

Molarity)

17Calculating the pH

pH = - log [H+](Remember that the [ ] mean Molarity)

Example: If [H+] = 1 X 10-10

pH = - log 1 X 10-10

pH = - (- 10)pH = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74)pH = 4.74

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Acid/Base definitions

Arrhenius (Swedish chemist)

19Arrhenius acid is a substance that produces (dissociates – i.e. breaks down) into H+ in water

HCl (aq) H+ (aq) + Cl- (aq)

Arrhenius base is a substance that produces (dissociated, i.e breaks down) into OH- in water

NaOH (aq) ---> Na+ (aq) + OH- (aq)

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Let’s Try This Work Sheet

21Strong and Weak Acids/Bases

The strength of an acid (or base) is determined by the amount of dissociation.

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• Weak acids are a lot less than 100% dissociated

in water.

STRONG VS WEAK Acids

• A strong acid or base is one that is completely 100% dissociation water.

HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids. Most acids are weak.

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Example: Weak Acid : Acetic Acid - Vinegar

• CH3COOH + H2O CH3COO– + H+

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• Strong Base: 100% dissociated in water.

NaOH (aq) ---> Na+ (aq) + OH- (aq)

Strong Bases

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Weak base: less than 100% ionized in waterOne of the best known weak bases is ammonia

NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

Weak Bases

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Weak Bases

27How Strength relates to Conductivity