1 IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL CHEM 122. LEVEL-2 LECTURE# 2 CHAPTER 9 – ACIDS & BASES Chemistry by Timberlake p.266 RCDPR Presented by: Department Of Chemistry

2 Modern Concepts of Acids and Bases Three important theories of acids and bases. (1) ARRHENIUS THEORY An acid: is a substance that contains hydrogen and ionizes in aqueous solution to give hydrogen ion. A base: is a substance that contains hydroxyl group and gives hydroxyl ions in aqueous solution.

3 Arrhenius Acids and Bases P-267 Acids produce H + in aqueous solutions water HCl H + (aq) + Cl - (aq) Bases produce OH - in aqueous solutions water NaOH Na + (aq) + OH - (aq)

4 2) BRONSTED – LOWRY THEORY An acid is a substance that exhibits (shows) a tendency to lose one or more protons. A base is a substance that exhibits (shows) a tendency to gain protons.

5 Bronsted-Lowry Acids P-270 Acids are hydrogen ion (H +) donors Bases are hydrogen ion (H + ) acceptors HCl + H 2 O H 3 O + + Cl - ++ donor acceptor + -

6 (3) LEWIS ACID – BASE THEORY -An acid is any molecule or ion that can accept a pair of electrons and form a coordinate covalent bond. -A base is any molecule or ion that can donate a pair of electrons and form a coordinate covalent bond - Electron pair acceptor is an acid and electron pair donor is a base. BF 3 + :NH 3 → BF 3 : NH 3 Acid Base

7 Some Common Acids P-268 I-The name of a non-oxy acid begins with the prefix hydro- and ends with -ic acid. In a non-oxy acid, the negative anion end in -ide. HCl hydrochloric acid (Cl- is choride) HBr hydrobromic acid (Br- is bromide) II-The name of an oxy acid is named with the stem of the anion (carbonate) changed to -ic acid HNO 3 nitric acid (NO3- is nitrate) H 3 PO 4 phosphoric acid ( PO4- is phosphate) H 2 SO 4 sulfuric acid ( SO4- is sulfate) CH 3 COOH acetic acid (CH3COO- is acetate) H2CO3 carbonic acid (CO 3 -2 is carbonate).

8 Some Common Bases P-269 NaOHsodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide Mg(OH) 2 magnesium hydroxide Al(OH) 3 aluminum hydroxide

9 Acids-Properties P-267 þ Produce H + (as H 3 O + ) ions in water þ Produce a negative ion (-) too þ Taste sour þ Corrode metals þ Are electrolytes þ React with bases to form salts and water

10 Bases-Properties P-269  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water

11  Conjugate Acids and Bases P-271 When an acid loses a proton, the residue will have the tendency to accept it back. The residue is therefore behaves as a base. AH ⇌ H + + B - Acid conjugate base An acid and base, which differ by a proton, this relationship are said to form a conjugate pair. Thus every acid has its conjugate base and every base has its conjugate acid.

12 Acid Conjugate base NH + 4 ⇌ H + + NH 3 HCO - 3 ⇌ H + + CO 3 2- CH 3 COOH ⇌ H + + CH 3 COO - HCl ⇌ H + + Cl - -Acids and bases may be ions or molecules but one of the member of conjugate pair is always an ion.

13 Conjugate Acids and Bases P-271 Role of solvents in Acids and Bases : -HCl behaves as an acid in its aqueous solution. -HCl does not behave as an acid in benzene (it does not show its acidic properties). -This is because “ A substance will behave as an acid only when another substance capable of accepting a proton, i.e. a base of some kind, is present.”

14 -In aqueous solution of HCl, molecules of water are able to take up protons and water acts as a base. HCl + H 2 O ⇌ H 3 O + + Cl - Acid I Base II Acid II Base I | | Base I is a conjugate base of Acid I and Acid II is a conjugate acid of a Base II

15 Conjugate Acids and Bases Acid IBase IIAcid II Base I H 2 O +NH 3 ⇌ NH OH - H 2 O +CH 3 COO - ⇌ CH 3 COOH + OH - CH 3 COOH +NH 3 ⇌ NH CH 3 COO - NH 3 +NH 3 ⇌ NH NH - 2 HF +HF ⇌ H 2 F + + F - H 2 O +H 2 O ⇌ H 3 O + + OH - -It is seen from the above example that, the strong acids have weak conjugate bases, while weak acids have strong conjugate bases. -NH 3, H 2 O, HF have dual character of acids & bases are called amphiprotic.

16 Describe the type of solution in each of the following as: 1) acid 2) base or 3)neutral. A. ___soda B. ___soap C. ___coffee D. ___ wine E. ___ water F. ___ grapefruit

17 Answer: Describe each solution as: 1) acid 2) base or 3) neutral. A. _1 _ soda B. _2_ soap C. _1_ coffee D. _1_ wine E. _3_ water F. _1_ grapefruit

18 Identify each as characteristic of an A) acid or B) base ____ 1. Sour taste ____ 2. Produces OH - in aqueous solutions ____ 3. Chalky taste ____ 4. Is an electrolyte ____ 5. Produces H + in aqueous solutions

19 Answer: Identify each as a characteristic of an A) acid or B) base _A_ 1. Sour taste _B_ 2. Produces OH - in aqueous solutions _B_ 3. Chalky taste A, B 4. Is an electrolyte _A_ 5. Produces H + in aqueous solutions

20 Q: Give the names of the following A. HBr (aq)1. bromic acid 2. bromous acid 3. hydrobromic acid B. H 2 CO 3 1. carbonic acid 2. hydrocarbonic acid 3. carbonous acid P-268

21 Answer: A. HBr3. hydrobromic acid B. H 2 CO 3 1. carbonic acid