When NaOH solution is gradually added to the solution of a weak acid (HA), the pH of the solution is found to be 5.0 at the addition of 10.0 mL of NaOH and 6.0 at the further addition of 10.0 mL of same NaOH.(Total volume of NaOH=20 mL) calculate pK_a for HA[log 2 =0.3] [Fill your answer in the form of multiple of 10^(-1) for example if your answer is 2.1 then fill 21 as your answer ]

When NaOH solution is gradually added to the solution of a weak acid (

1.	When NaOH solution is gradually added to the solution of a weak acid (HA), the pH of the solution is found to be 5.0 at the addition of 10.0 mL of NaOH and 6.0 at the further addition of 10.0 mL of same NaOH.(Total volume of NaOH=20 mL) calculate pK_a for HA[log 2 =0.3] [Fill your answer in the form of multiple of 10^(-1) for example if your answer is 2.1 then fill 21 as your answer ]
Answer» Solution :LET initial conc. Of HA & NaOH be `C_1 & C_2`mol/L and initial volume of HA=`V_1mL` `therefore 5.0=pK_a+"LOG"(10C_2)/((C_1V_1-10C_2))`...(1) `6.0=pK_a+"log"(20C_2)/((C_1V_1-20C_2))`...(2)from these we get `C_1V_1=22.5 C_2` `:.5.0=pK_a+"log"(10C_2)/(22.5C_2-10C_2)=pK_a+log(0.8)` `:. pK_a=5.1`