Step 3. Calculate solution's pH value when add hydrochloric acid HAC H++ AC Starting 0.10 0.10 Change +0.01 -0.01 Equilibrium 0.10+0.01 0.10-0.01 Step 4. Substitute the equilibrium concentration into the equilibrium-constant equation H+]=Ka×[ HACVAC] =1.70×10-5×0.11/0.09 =2.07×103 H=4.68 ApH=..68-0.09(pH unit)Step 3. Calculate solution’s pH value when add hydrochloric acid HAc H+ + Ac￾Starting 0.10 0.10 Change +0.01 -0.01 Equilibrium 0.10+0.01 0.10-0.01 Step 4. Substitute the equilibrium concentration into the equilibrium-constant equation [H+ ] = Ka  [HAc]/[Ac- ] = 1.70  10-5  0.11/ 0.09 = 2.07  10-5 pH = 4.68  pH = 4.77–4.68= 0.09 (pH unit)