3.3C PREDICTING THE STRENGTH OF BASES The principle which allows us to estimate the strengths of bases the stronger the acid the weaker will be its conjugated base So relate the strength of a base to the pKa of its conjugate acid The larger the pKa of the conjugate acid, the stronger is the base increasing base strength CH2CO OH Very weak base pKa of conjugate Strong base pKa of conjugate acid(CH3 H) pKa of conjugate acid(HCI)=-7 4.75 acid(H2O)=15.73.3C PREDICTING THE STRENGTH OF BASES The principle which allows us to estimate the strengths of bases: the stronger the acid, the weaker will be its conjugated base. So relate the strength of a base to the pKa of its conjugate acid. The larger the pKa of the conjugate acid, the stronger is the base. increasing base strength Cl - CH3 CO2 - OH - Very weak base pKa of conjugate acid (HCl) = - 7 pKa of conjugate acid (CH3 CO2 H) = 4.75 Strong base pKa of conjugate acid (H2 O) = 15.7