A compound is known to have a free amino group with a pka of 8.8,and one other ionizable group with a pka between 5 and 7. To 100mLof a 0.2M solution of this compound at pH8.2 was added 40 mL of asolution of 0.2 M hydrochloric acid. The pH changed to 6.2. The pKaof the second ionizable group is: