1 4.7 Acids and Bases

Properties of Acids and Bases Acid Base - pH 7 - tastes sour- tastes bitter - no special feel- feels slippery - turns blue litmus red- turns red litmus blue - neutralizes a base- neutralizes an acid - e.g. HCl- e.g. NaOH

Arrhenius Theory of Acids and Bases ACIDS = ionic compounds that ionize in water and release H + ions e.g. HCl (s)  H + (aq) + Cl - (aq) e.g. HNO 3(s)  H + (aq) + NO 3 - (aq) BASES = ionic compounds that dissociate in water and release OH - ions e.g. LiOH (s)  Li + (aq) + OH - (aq) e.g. Ca(OH) 2(s)  Ca 2+ (aq) + 2 OH - (aq)

You Try H 3 PO 4(s)  Al(OH) 3(s) 

Strong and Weak Acids A strong acid will completely ionize in water (lower pH and react vigorously) e.g. HCl (aq)  H + (aq) + Cl - (aq) A weak acid will partially ionize in water (higher pH and react less vigorously) e.g. HC 2 H 3 O 2(aq)  H + (aq) + C 2 H 3 O 2 - (aq)

The Strength of Acids & Bases Weak acids have fewer molecules dissociate or break up and thus the number of hydrogen ions is less. The more hydrogen ions there are, the lower the pH value. Similarly, weak bases have fewer molecules dissociate and thus the number of hydroxide ions is less The more hydroxide ions there are, the higher the pH value.

Concentration & Strength Both strong and weak acids can be concentrated or dilute. For Example, I can create both a 10 mol/L solution and a 0.01 mol/L solution of HCl (aq) In both cases, however, hydrochloric acid (HCl (aq) ) is considered a strong acid because all of the HCl molecules are ionized.

pH and Acidity pH = 7, neutral pH > 7 = basic pH < 7= acidic a pH change of 1 unit represents a 10-fold change in how basic or acidic a solution is e.g. Lemon juice (pH = 2) is 10x more acidic than pop (pH = 3)

pH Scale

Reaction of an Acid and a Base When you mix an acid and a base, you create water and a salt (ionic compound) This is a double displacement reaction For example: HCl (aq) + NaOH (aq) 

Homework Read pp. 293 – 303 Answer the following questions:  p. 300 # 2, 3  p. 304 # 3, 4, 6, 7, 11