1) Strong base is dissolved in 675 mL of 0.200 M weak acid (Ka = 4.10 times 10-5
ID: 840690 • Letter: 1
Question
1)
Strong base is dissolved in 675 mL of 0.200 M weak acid (Ka = 4.10 times 10-5) to make a buffer with a pH of 4.17. Assume that the volume remains constant when the base is added. HA(aq) + OH-(aq) rightarrow H2O(l) + A-(aq) Calculate the pKa value of the acid and determine the number of moles of acid initially present. When the reaction is complete, what is the concentration ratio of conjugate base to acid? How many moles of strong base were initially added? Calculate the pH for each of the following cases in the titration of 50.0 mL of 0.200 M HCIO(ag) with 0.200 M KOH(aq). The ionization constant for HCIO can be found here. before addition of any KOH after addition of 25.0 mL of KOH after addition of 30.0 mL of KOH after addition of 50.0 mL of KOH after addition of 60.0 mL of KOHExplanation / Answer
ka=4.1x10-5
pka=-log(4.1x10-5)=4.39
number of moles=0.675L*0.2moles/L=0.135moles
==
HA+H2O<==>A- + H3O+
0.2-x.................x...........x
4.17=4.39+log[salt]/[acid]
4.17-4.39=log[salt]/[acid]
-0.22=log[salt]/[acid]
0.602=[salt]/[acid]
0.602=x/0.2-x
0.1204-0.602x=x
0.1204=x+0.602x=1.602x
x=0.1204/1.602=0.075=molarity of strong Base added=salt formed
moles of base added=0.075moles/L*0.675L=0.0506moles
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