Chapter. Acid-Base Concept. Table of Contents. Introduction 1. Acid-Base Theories 2. The ph Scale 3. Strength of Acids and Bases 4.

Transcription

1 Acid-Base Concept Table of Contents Introduction 1. Acid-Base Theories 2. The ph Scale 3. Strength of Acids and Bases 4. Neutralization

2 Acid-Base Concept Warm up Think about substances that you encounter in a typical day and make two lists. One list should contain substances that might be acids. The other should contain substances that might be bases.

3 Acid-Base Concept

4 Introduction The term acid is acere, in Latin language, meaning sour. In 17 th century the English chemist Robert Boyle grouped the substances as either acids or bases. Acids and bases are found in many fruits, vegetables and some household products, like vinegar, apple, oranges, lemons, grapes, soaps, etc. To explain the behavior of acids and bases there are many acid-base theories.

5 1. Acid-Base Theories 1. General Properties of Acids Are generally sour in taste, Are corrosive substances Change the color of litmus paper to red, React with metals to produce a metal salt and hydrogen gas, React with metal carbonates to produce water, CO 2 and a salt, React with bases to produce water and a salt, neutralization reaction, Conduct electricity.

6 1. Acid-Base Theories 2. General Properties of Bases Are generally bitter in taste, Cause slippery feeling to skin, Change the color of litmus paper to blue, Strong bases are corrosive, React with amphoteric metals to produce a metal salt and hydrogen gas, React with bases to produce water and a salt, neutralization reaction, Conduct electricity.

7 The ph Scale The Arrhenius Acid-Base Theory In 1884, Swedish chemist Svante Arrhenius defined acids as compounds that produce H + ions in aqueous solutions, and bases compounds that produce OH - ions in aqueous solutions. This theory was insufficient to explain the acidic or basic properties of some substances such as SO 3 or NH 3.

8 3. The ph Scale

9 Indicators and The ph Scale ph is a measure of the acidity or basicity of a solution.

10 4. Strength of Acids and Bases Acid Strength

11 4. Strength of Acids and Bases Base Strength

12 Chapter 5 3. The ph Scale ph is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the concentration of dissolved hydrogen ions (H + ). It varies between 0 to 14. Indicators are used to determine the acidity level of solutions. + + ph = log H or H = 10 ph Similarly for [OH - ] ion poh can be expressed as; poh = log OH or OH = 10 poh

13 Chapter 5 3. The ph Scale For pure water at 25 o C, [H + ]= 1x10-7 M and [OH - ]= 1x10-7 M. [H + ]= 1x10-7 M and [OH - ]= 1x10-7 M. ph=-log(1x10-7 ) = 7 and poh=-log(1x10-7 ) = 7 ph + poh = 14 The ph value of a solution gives an idea about the condition of a solution as follows; if ph<7.0 solution is acidic, if ph= 7.0 solution is neutral, if ph >7.0 solution is basic.

14 Acid-Base Theories 1. The Arrhenius Acid-Base Theory In 1884, Swedish chemist Svante Arrhenius defined acids as compounds that produce H + ions in aqueous solutions, and bases compounds that produce OH - ions in aqueous solutions. This theory was insufficient to explain the acidic or basic properties of some substances such as SO 3 or NH 3. HCl(aq) HNO 3 (aq) NaOH(s) Mg(OH) 2 (s) Cl - (aq) + H + (aq) NO - 3 (aq) + H + (aq) Na + (aq) + OH - (aq) Mg +2 (aq) + 2OH - (aq)

15 Chapter 5 Ionization of Water Water is a amphoteric substance, acting as a base against acids and as an acid against bases. H 2 O(I) + H 2 O(I) OH - (aq) + H 3 O + (aq) Equilibrium constant expression for the ionization of water is Kw=[H 3 O + ] [OH - ] at 25 o C Kw has a value Kw=1x10-14 when water is neutral Kw=[H 3 O + ] [OH - ]=1x10-14, then [H 3 O + ]= [OH - ]=1x10-7 M.

16 Chapter 5 3. The ph Scale Example 4 Calculate the ph and poh of the solutions given below. a. A solution with a [H + ] of 1x10-3 M. b. A solution with a [OH - ] of 1x10-3 M. c. A solution with a [H + ] of 5x10-7 M. d. A solution with a [OH - ] of 8x10-11 M.

17 Chapter 5 3. The ph Scale Example 7 Fill the following table for each of the solution. Solution [H + ] [OH - ] ph poh 0.05 M NaOH 0.05 M H 2 SO M Ca(OH) 2

18 Acid-Base Theories 1. The Arrhenius Acid-Base Theory

19 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory It was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in An acid is defined as any chemical species (molecule or ion) that is able to lose, or "donate" a hydrogen ion (proton), and a base is a species with the ability to gain or "accept" a hydrogen ion (proton). conjugate acid-base pair NH 3 (g) + H 2 O(l) NH + 4 (aq) + OH - (aq) base 1 acid 2 acid 1 base 2 conjugate acid-base pair

20 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory

21 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory

22 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory

23 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory Example 1 Show the conjugate acid-base pairs in the following reaction. CH 3 COOH + H 2 O CH 3 COO - + H 3 O + Solution CH 3 COOH and CH 3 COO -, H 2 O and H 3 O + are conjugate acid base pairs

24 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory Example 2 Write the conjugate acids of the following bases. a. OH - b. CN - c. ClO - d. S -2 Solution a. H 2 O b. HCN c. HClO d. HS -

25 1. Acid-Base Theories 2. Bronsted Lowry Acid-Base Theory Example 3 Write the conjugate bases of the following acids. a. HCO - 3 b. H 3 O + c. CH 3 NH + 3 d. HS - Solution a. CO 3-2 b. H 2 O c. CH 3 NH 2 d. S -2

26 1. General Properties of Acids 1. Acid-Base Theories

27 2. General Properties of Bases 1. Acid-Base Theories

28 2. General Properties of Bases 1. Acid-Base Theories

29 2. General Properties of Bases 1. Acid-Base Theories