A buffer solution that is 0.325 M in HCN and 0.325 M in KCN has a pH of 9.40. Ad
ID: 500744 • Letter: A
Question
A buffer solution that is 0.325 M in HCN and 0.325 M in KCN has a pH of 9.40. Addition of which of the following would increase the capacity of the buffer for added H3O+?
both HCN and KCN
pure water
HCN
KCN
None of the Above
One or more of these choices is the answer, please answer in that format. I have already asked this question and got the wrong answer.
A buffer solution is made that is 0.388 M in HCN and 0.388 M in NaCN.
(1) If Ka for HCN is 4.00×10-10, what is the pH of the buffer solution?
(2) Write the net ionic equation for the reaction that occurs when 0.114 mol NaOH is added to 1.00 L of the buffer solution.
The last person who answered this didn't get it right.
Explanation / Answer
A buffer solution that is 0.325 M in HCN and 0.325 M in KCN has a pH of 9.40. Addition of which of the following would increase the capacity of the buffer for added H3O+?
Capacity of buffer for H3O+, i.e., what do we need to do to increase change of pH when H+ addition:
both HCN and KCN
pure water --> Not really, since this will only dilute the system, but the ratio of acid/base remains the same
HCN --> this will NOT help, since HCN is acidic, and H+ is acidic as well
KCN --> This WILL help, since CN- will neutralize H+ addition to form HCN
None of the Above --> false, KCN is true
Q1.
for
HCN + NACN, this is a buffer so
pH = pKa + log(NaCN/HCN)
pKa = -log(Ka) = -log(4*10^-10) = 9.397
pH = 9.397 + log(0.388/0.388)
pH = 9.397
Q2.
Net ionic when we add
NAOH to the buffer:
base will react with acid so
NAOH(aq) + HCN(aq) --> H2OP(l) + NaCN(aq)
net ionic includes only those in that react in solution
H+(aq) + OH-(aq) --> H2O(l)
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