Chapter 21 Notes, part II Salt Hydrolysis Buffer Solutions

Salt Hydrolysis Remember, Acid+Base  Salt+Water Some salts are neutral, but others are acidic or basic. Why? Because some salts promote hydrolysis. Hydrolysis—the reaction of an ion with water

Salt Hydrolysis The cations or anions from the dissociated (dissolved in water) salt remove hydrogen ions from or donate hydrogen ions to water. Depending on the direction of the hydrogen ion transfer, the salt can be acidic or basic.

Strong Acid+Strong Base  Neutral Solution Strong Acid + Weak Base  Acidic Solution Strong Base + Weak Acid  Basic Solution Why is this?

Are the following salts going to be acidic, basic or neutral?

NaCl

NH 4 NO 3

KC 2 H 3 O 2

Ca(ClO 3 ) 2

FeBr 2

KMnO 4

MgSO 4

LiNO 3

ZnCl 2

AgBr

Buffers Buffer—A solution in which the pH remains relatively constant when a small amount of acid or base is added. A buffer is made by making a solution of a weak acid and its salt or a weak base and its salt.

How does a buffer work? EX: HC 2 H 3 O 2 and NaC 2 H 3 O 2 In soln, the following reactions take place HC 2 H 3 O 2  H + + C 2 H 3 O 2 - NaC 2 H 3 O 2  Na + + C 2 H 3 O 2 - If acid is added, the acetate ion acts like a H + sponge.C 2 H 3 O H +  HC 2 H 3 O 2 nIf a base is added, the acetic acid will neutralize it! HC 2 H 3 O 2 +OH -  C 2 H 3 O 2 - +H 2 O

Buffer Capacity The buffer capacity is the amount of acid or base that a buffer can hold before significant change in pH occurs.