A buffer solution is made that is 0.420 M in HCN and 0.420 M in KCN. If K_a for
ID: 1009199 • Letter: A
Question
A buffer solution is made that is 0.420 M in HCN and 0.420 M in KCN. If K_a for HCN is 4.00 times 10^-10, what is the pH of the buffer solution? Write the net ionic equation for the reaction that occurs when 0.091 mol HI is added to 1.00 L of the buffer solution. Use H_3 O^+ instead of H^+. + rightarrow + A 27.7 mL sample of 0.229 M triethylamine, (C_2 H_5)_3 N, is titrated with 0.234 M hydroiodic acid. At the titration midpoint, the pH is. Use the Tables link in the References for any equilibrium constants that are required.Explanation / Answer
1) pH of buffer = pka + log(salt/acid)
pka = -log(4*10^-10) = 9.4
= 9.4+log(0.42/0.42)
pH = 9.4
2)
H3O^+(aq) + CN-(aq) -----> HCN(aq) + H2O(l)
pkb of (C2H5)3N = -LOG(5.2*10^-4) = 3.284
At midpoint , No of mol of (C2H5)3N = No of mol of HI
pOH = PKb
pH = 14-3.284 = 10.716
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