Acidic,basic or neutral? [16.9] Salts Acidic,basic or neutral?

Acid and Base Strength Strong acids are completely dissociated in water. Their conjugate bases are quite weak. Weak acids only dissociate partially in water. Their conjugate bases are weak bases.

Effect of Cations and Anions An anion that is the conjugate base of a strong acid will not affect the pH. An anion that is the conjugate base of a weak acid will increase the pH. A cation that is the conjugate acid of a weak base will decrease the pH.

Effect of Cations and Anions Cations of the strong Arrhenius bases will not affect the pH. Other metal ions will cause a decrease in pH. When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base, the affect on pH depends on the Ka and Kb values.

Factors Affecting Acid Strength The more polar the H-X bond and/or the weaker the H-X bond, the more acidic the compound. Acidity increases from left to right across a row and from top to bottom down a group.

Acid + base = salt + water Many ions react with water to produce H+ or OH- ions = HYDROLYSIS Neutral, basic or acidic solutions…where did the salt come from? (its parents) KCl or NaC2H3O2 or NH4NO3 or FeCl3

Neutral Salt Solutions Cations from strong bases and anions of strong acids Conjugate ions have negligible effect on pH KCl, KNO3, NaCl, NaNO3 Whose from KOH? NaOH? HCl? HNO3?

Basic Salt Solutions Cation is neutral (from strong base) and anion is the conjugate base of a weak acid NaC2H3O2, KCN, NaF Cations from NaOH or KOH, strong bases Anions from HC2H3O2, HCN, HF = weak acids C2H3O2- + H2O  HC2H3O2 + OH-

Acidic Salt Solutions Anion from strong acid, cation is the conjugate acid of a weak base NH4Cl, NH4NO3 Metal ions (higher charge = higher acidity), other than group 1A or heavier members of group 2A (Ca+2, Sr+2, Ba+2) Al(NO3)3, FeCl3

What about salts of weak acids & weak bases? Need to compare strengths of the conjugates Ka vs Kb Acidic if Ka > Kb Basic if Ka < Kb Neutral if Ka = Kb