Question

Among the drugs diazepam (weak base, pKa 1.3), oxacillin (weak base, pKa 2.8), phenol (weak acid, pKa 9.9), and morphine (amphoteric, amine pKa 8.0, phenol pKa 9.6), which is the most highly ionized at a pH of 7.4?

Answer 1

As we know Pka = - log Ka value since Ka value is directly proportional to concentration of H+ ion so as the Ka value increase acidic character increase and PKa value decreases

So ka value of above mentioned compound will be as follows

Diazepam ka value 2.0 × 10^-1 (approx)

Oxacillin Ka value 6.4 × 10^-2 ( approx)

Phenol ka value 8.0 × 10^-9 (approx)

Morphine ka value 10^-8 (approx)

Phenol ka value 4.0 × 10^9 (approx)

So from the above data we know that pH 7.3 is weak basic medium in which acidic part will ionize faster and so in case of above compund Diazepam will ionize faster than oxacillin than morphine and then phenol