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From a GS exam-
Cyanide ions (CN-) could also have been used to precipitate the cations. If after all the cations have been precipitated, the concentration of CN- is 0.02 M, calculate the pH of the solution given that:
CN- + H2O --> HCN + OH-
Kb = 1.39 x 10-5
a 4.9
b 5.4
c 7.7
d 10.7
I sort of get how they solved it, by using the definition of Kb as a function of concentrations to find pOH and then pH, but in so doing they make the assumption that [HCN] = [OH]. Can someone tell me why this is a valid assumption?
thanks all
for those who are using this as practice for themselves, the correct answer is D
Cyanide ions (CN-) could also have been used to precipitate the cations. If after all the cations have been precipitated, the concentration of CN- is 0.02 M, calculate the pH of the solution given that:
CN- + H2O --> HCN + OH-
Kb = 1.39 x 10-5
a 4.9
b 5.4
c 7.7
d 10.7
I sort of get how they solved it, by using the definition of Kb as a function of concentrations to find pOH and then pH, but in so doing they make the assumption that [HCN] = [OH]. Can someone tell me why this is a valid assumption?
thanks all
for those who are using this as practice for themselves, the correct answer is D
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