JEE Advanced levelSingle correct optionDifficulty 3 of 3g2100
Methylammonium ion has pKa = 10.6 at 298 K. Using the weak-base approximation [OHX−]=Kbc, the pH of a 0.1M aqueous solution of methylamine is closest to
A2.2
B8.2
C12.8
D11.8
Answer: D
pKb=14−10.6=3.4. pOH=21(pKb−logc)=21(3.4+1)=2.2, so pH=14−2.2=11.8.