Calculate the approximate pH value of different solutions below ; (1) A 0.10 M HAc K a (HAc)=1.8×10 -5 (2) A 0.10 M NH 4 Cl K b (NH 3 )= 1.8×10 -5 (3) A mixture solution with 0.05 M NaHCO 3 (50 mL) and 0.10 M NaOH (16.5 mL) , then diluted to 100 mL. H 2 CO 3 : K a1 =4.2×10 -7 , K a2 =5.6×10 -11