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