You obtain a buffer that 0.496 moles of chlorous acid (HCIO2, Ka-1.10 x 10-2) an
ID: 948998 • Letter: Y
Question
You obtain a buffer that 0.496 moles of chlorous acid (HCIO2, Ka-1.10 x 10-2) and 0.496 moles of potassium chlorite (KCIO2) dissolved in 1.00 L of solution. What is the pH of the buffer? Part #1: Part #2: To the buffer in part 1, you add 0.160 moles of potassium hydroxide (KOH), write the reaction of the buffer with the base. After, complete an ICE table calculating the END moles of each substance after the reaction. Hint: consider potassium hydroxide to react COMPLETELY Which of the following represents the END moles of HCIO2 and CIO2 after reaction? OA HCIO2: 0.656 moles CIo2 CIO2: 0.656 moles O BHCIO2: 0.656 moles CIo2 CO,-: 0.336 moles O C HCIO2: 0.336 moles CIO2:0.336 moles O D HCIO2: 0.336 moles CIO2: 0.656 molesExplanation / Answer
1. From Henderson equation pH of a buffer is:
pH = pKa + log [salt]/[acid]
[salt] = [KClO2] = 0.496 M
[acid] = [HClO2] = 0.496 M
pH = 0.011 + log 0.496/0.496 = 0.011
2. KOH will react with HClO2 to give more salt.
HClO2 + KOH = KClO2 + H2O
initial(moles): 0.496 0.16 0 0
final(moles): 0.496-0.16 0 0.16 0.16
[HClO2] after reaction = 0.496-0.16 = 0.336 moles
[KClO2] after reaction = 0.496 + 0.16 = 0.656 moles
3. pH = pKa + log [salt]/[acid]
= 0.011 + log 0.656/0.336 = 0.302
4. pH = pKa + log [salt]/[acid]
= 0.011 + log 0.496/0.255
= 0.299
5. KOH will react with HClO2 to give more salt.
HClO2 + KOH = KClO2 + H2O
initial(moles): 0.255 0.16 0 0
final(moles): 0.255-0.16 0 0.16 0.16
[HClO2] after reaction = 0.255-0.16 = 0.095 moles
[KClO2] after reaction = 0.496 + 0.16 = 0.656 moles
pH = pKa + log [salt]/[acid]
= 0.011 + log 0.656/0.095
= 0.850
6. It is generally accepted that buffer capacity of a buffer solution is +-1 of pKa (buffer is effective within the range 1 acid to 10 salt or vice versa].
When KOH is 10 times the acid in the solution then the buffer is overwhelmed. So KOH have to be added
= 10*0.496 - 0.496
= 4.464 moles
7. minimum moles of KOH
= 10*0.255 - 0.496
= 2.054 moles
8. B. The solution in part 1 because buffer requires more strong acid /base to overwhelm the buffer (a buffer will be a best buffer if its pH is closer to the value of pKa/pKb, because in this condition it is needed more acid/base to overwhelm the buffer.]
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