1 The Chemistry of Acids and Bases

2 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”

3 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”

4 Acid and Bases

5

6

7 Indicators 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

8 Examples: Indicators Litmus paperLitmus paper PhenolpthaleinPhenolpthalein Bromothymol blueBromothymol blue Methyl OrangeMethyl Orange

9

10 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.

12 pH meter When precise measurement of pH required.When precise measurement of pH required. Tests the voltage of the electrolyteTests the voltage of the electrolyte Converts the voltage to pHConverts the voltage to pH Must be calibrated with a buffer solutionMust be calibrated with a buffer solution

13 pH of Common Substances

14 The 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. The 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)

15 The pH scale is a way of expressing the strength of acids and bases. Under 7 = acid 7 = neutral Over 7 = alkaline (base)

16 pH 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)

17 Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

18 Acid/Base definitions Arrhenius (Swedish chemist)

19 Arrhenius 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)

20 Let’s Try This Work Sheet

21 Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of dissociation.

22 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. HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Most acids are weak.

23 Example: Weak Acid : Acetic Acid - Vinegar CH 3 COOH + H 2 O CH 3 COO – + H +

24 Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) Strong Bases

25 Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Weak Bases

26

27 How Strength relates to Conductivity