Transcription of POLYPROTIC ACIDS AND BASES: Very important!
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POLYPROTIC ACIDS AND BASES: Very important!
18-1 POLYPROTIC ACIDS AND BASES: Very important! -- ACIDS that can lose, and bases that can pick up, more than one H+ ( diprotic H2A and triprotic H3A ACIDS ). Ionization occurs stepwise, and each step has its own Ka. H3PO4 (aq) H+ (aq) + H2PO4- (aq) Ka1 = x 10-3 increasing H2PO4- (aq) H+ (aq) + HPO42- (aq) Ka2 = x 10-8 acid HPO42- (aq ) H+ (aq ) + PO43- (aq ) Ka3 = x 10-13 strength Note: (i) Ka1 > Ka2 > Ka3 Always true for POLYPROTIC ACIDS , , each ionization step is more difficult because it is more difficult to remove H+ from a molecule as its negative charge increases. BUT this does not apply for ionic salts of these ACIDS , , Na3PO4, Na2SO4, etc.
18-9 NOTE: (i) pK b = -log K b (ii) just like pK a, strength of base increases with decreasing pK b (See Table 18.6) The bigger is K b, the more OH-is generated. The smaller is pK b, the more OH-is generated. base formula K b pK b Diethylamine NHEt 2 8.6 x 10-4 3.07 Methylamine NH 2Me 4.4 x 10-4 3.36 Ammonia NH
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