Strong Acid An acid that nearly completely dissociates All molecules of the acid break up to form the ions soluble in water

Weak Acid An acid that only slightly dissociates in a water solution Only a small percent of acid molecules donate their hydrogen. Example: CH3COOH

Examples of Strong Acids and Bases Strong Acids Strong Bases HClO4 perchloric acid LiOH lithium hydroxide HCl hydrochloric acid NaOH sodium hydroxide HNO3 nitric acid KOH potassium hydroxide H2SO4 sulfuric acid RbOH rubidium hydroxide HBr hydrobromic acid CsOH cesium hydroxide HI hydriodic acid Ca(OH) 2calcium hydroxide Sr(OH) 2strontium hydroxide Ba(OH)2 barium hydroxide

A- H+ A- H+ A- H+ A- H+ A- H+ Acids: Concentration vs. Strength CONCENTRATED DILUTE H+ A- H+ A- H+ A- H+ A- HA A- H+ A- H+ A- H+ A- H+ A - H+ A- HA H+ A- H+ A- H+ A- A- H+ A- H+ A- H+ A- H+ A- H+ H+ A - H + A - H + A - HA H + A - A- H+ A- H+ A- H+ A- H+ A– H+ A- H+ A- H+ A- H+ A- H+ A- H+ A- H+ A- H+ A- H+ A- HA A- H+ A- H+ A- H+ A- H+ H+ A - H+ A - HA A - H+ A - H+ A – H+ A - H+ A - H+ A - HA H+ A - H+ A - H+ A - H+ STRONG ACIDS Dissociate nearly 100% HA H1+ + A- WEAK ACIDS Dissociate very little HA H1+ + A- STRONG HA HA H+ A- HA HA HA HA HA HA HA HA H+ A- H+ A- HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA H+ A- HA HA H+ A- HA HA HA HA HA HA HA HA H+ A- HA HA H+ A- HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA HA HA HA HA H+ A - HA HA HA HA H + A – HA H + A – HA HA Strong acids react essentially completely with water to give H+ and the corresponding anion. Strong bases dissociate essentially completely in water to give OH– and the corresponding cation. Both strong acids and strong bases are strong electrolytes. Only a fraction of the molecules of weak acids and weak bases react with water to produce ions and are, therefore, weak electrolytes. No correlation between solubility in water and whether a substance is a strong or a weak electrolyte. WEAK

A strong acid essentially ionizes 100%. Ex: A strong acid is hydrochloric acid, HCl (aq), say @ 0.10 M, what is the pH? HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) I 0.10 mol 0.00 mol 0.00 mol C -x no +x +x E almost zero 0.10 mol 0.10 mol pH is 1.00 We have 100% ionization no molecules all ions HCl(g) H3O+(aq) and Cl-(aq)

WEAK ACID An example of a weak acid is acetic acid, CH3COOH, Say at 0.10 M and 1.3% ionization. CH3COOH(l) + H2O(l)  H3O+(aq) + CH3COO-(aq) 1.00 mol/dm-3 0.013mol mol/dm- 0.013 mol/dm-3 1.3% ionization at 25C of [1.0] = 0.013 mol/dm-3 Most stays as molecules, very few ions

Equilibria Involving A Weak Acid You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, H3O+, OAc-, and the pH, where Ka = 1.8 x 10 -5 Step 1. Define equilibrium concs. in ICE table. [HOAc] [H3O+] [OAc-] initial change equilib 1.00 0 0 -x +x +x 1.00-x x x

x = [H3O+] = [OAc-] = 4.2 x 10-3 M pH = - log [H3O+] = -log (4.2 x 10-3) = 2.37

Strong vs. Weak Acid A salt can dissolve in water to produce a neutral, basic, or acidic solution, depending on whether it contains the conjugate base of a weak acid as the anion (A–) or the conjugate acid of a weak base as the cation (BH+), or both. • Salts that contain small, highly charged metal ions produce acidic solutions in water. • The most important parameter for predicting the effect of a metal ion on the acidity of coordinated water molecules is the charge-to-radius ratio of the metal ion. • The reaction of a salt with water to produce an acidic or basic solution is called a hydrolysis reaction, which is just an acid-base reaction in which the acid is a cation or the base is an anion. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 508

Equilibria Involving A Weak Base You have 0.010 M NH3. Calc. the pH, Kb = 1.8 x 10-5 NH3 + H2O  NH4+ + OH- Step 1. Define equilibrium conc. in ICE table [NH3] [NH4+] [OH-] initial change equilib 0.010 0 0 -x +x +x 0.010 - x x x X2 = 1.8 x 10 -7 Solve for x = 4.24 x 10 -4 pOH = 3.37 so pH = 10.63