Acids: Bases:

Properties of Acids : A CIDS Taste sour. Cause blue litmus paper to turn pink. Form H 2 (g) in front of active metals. Form CO 2 (g) in front of carbonates. Produce H + when dissolve in water. H + (aq) HCl(aq) → H + (aq) + Cl - (aq) (Arrhenius Model)

Properties of Bases :Bases Cause red litmus paper to turn blue. Taste bitter & feel slippery. (Soap) Cause phenolphthalein to turn red. Produce OH - when dissolve in water. NaOH(s) → Na + (aq) + OH - (aq) (Arrhenius Model)

Ion Product Constant for Water (Kw): K w =1.0 x H 2 O(l) H + H + (aq) + OH - (aq) acid acid base neutral neutral () (1.0 x ) () (1.0 x ) x xx xx K w = [H + ] [OH - ] 1.0 x

Example: If the H + ion concentration of an aqueous solution is 1 x M. What is the OH - ion concentration? Is the solution acid, basic, or neutral? [H + ] =1 x M K w = 1.0 x [OH - ] = ? K w = [H + ] [OH - ] [OH - ] = [OH - ] = 1.0 x ÷ 1 x [OH - ] = 1.0 x (-5) = 1.0 x [OH - ] = 1 x M (Makes sense?) acidic The solution is acidic H + > (Because [H + ] > [OH - ] )

10 -3 M K w ( ) = [H + ] [OH - ] M Solution acidic M M basic M M acidic M M neutral Conclusion: If [H + ] > [OH - ] acidic. The solution is acidic. < [OH - ] If [H + ] < [OH - ] basic. The solution is basic. = [OH - ] If [H + ] = [OH - ] neutral. The solution is neutral. > = < < < < > pH:

The pH Scale:

pH Scale: Acidic Acidic level increases Neutral Neutral solution Basic Basic level increases The pH indicates the acidity level of a solution.

pH and pOH : pH: Is the negative logarithm of the [H + ]. pH = - log [H + ] Example: [H + ] =1 x M pH= - log [H + ] = -log = - (-6) = 6 pH= 6 = -(-6) log 10 1

10 -3 M K w ( ) = [H + ] [OH - ] M Solution acidic M M basic M M acidic M M neutral Conclusion: < If pH < 7 acidic. The solution is acidic. > If pH > 7 basic. The solution is basic. = 7 If pH = 7 neutral. The solution is neutral. > = < < < < > pH:

pH and pOH : pOH : Is the negative logarithm of the [OH]. pOH = - log [OH - ] [H + ] [OH - ] = K w x = pH = -log = -(-7) = 7 7 pOH = -log = -(-7) = = 14 pH + pOH = 14

Example: Calculate the pH and pOH of a solution in which [H + ] = 1 x M. [H + ] =1 x M pH = ? pOH = ? pH= - log [H + ] = -log = - (-4) = 4 pH= 4 (acidic) pH + pOH = pOH = 14 pOH = pOH = 10

[H + ] = M pH= 4 [H + ] = [OH - ] = If pH= 8 [H + ] = pH= 8 pOH = [OH - ] = M M 10 -pOH 10 -pH

Complete the following table: [H + ] [OH - ] pH pOH acid base neutral 1x10 -4 M 1x10 -6 M 7 1 1x M 4 x 10 1x10 -8 M 8 6 x 1x10 -7 M 1x10 -7 M 7 x 1x10 -1 M 1x M 13 x

Neutralization

Reactions of Acids and Bases: 16

Neutralization Reactions: HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l) 17 baseacidsaltwater In a neutralization reaction, - an acid reacts with a base to form salt and water, - the salt is formed by the anion of the acid and the cation of the base.

Neutralization Reactions: Al(OH) 3(s) + 3 HBr (aq)  AlBr 3(aq) + 3 H 2 O (l) Mg(OH) 2(s) + H 2 SO 4 (aq)  MgSO 4(aq) + 2 H 2 O (l) base acid salt water water acid + base  salt + water

Basic Compounds in Antacids 19

Acid - Base Indicators: Acid - base indicators (also known as pH indicators) are substances which change color with pH. They are usually weak acids or bases. Examples: Red litmus paper Turns blue in from of bases. Blue litmus paper Turns red in from of acids. Phenolphthalein Pink in from of bases colorless in from of acids

Exercise: Complete the following table: HCl (aq) Mg(OH) 2 (aq) H 2 SO 4 (aq) Lemon juice KOH (aq) Blue litmus paper Red litmus paper Phenolphthalein No change Red No change Red Red Blue No change Blue No change No change Pink No change Pink No change No change

Estimating the pH of a solution: - Phenolphthalein – turns to colorless - Bromophenol blue – turns to purple - Bromocresol green – stays green - Congo red—stays red. pH < 8.3 > – 5.4 > 5.0 pH 5.0 – < – – – 5.4