For a solution that contains 0.10 M HCN and 0.10 M NaCN, whi

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Discussion Overview

The discussion revolves around a homework problem concerning a solution containing 0.10 M HCN and 0.10 M NaCN, specifically identifying which statement about the solution is false. The scope includes conceptual understanding of acid-base chemistry, the common ion effect, and equilibrium principles.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants identify HCN as the acid and NaCN as the conjugate base, noting a 1:1 concentration ratio.
  • One participant proposes the reaction HCN + NaOH → H2O + NaCN and attempts to relate it to the expression for Ka.
  • There is uncertainty regarding the common ion effect, with one participant unsure about its definition and implications for the solution.
  • Another participant suggests that the [H+] would be larger if only HCN were present, indicating a potential falsehood in statement B.
  • One participant agrees that addition of NaOH would shift equilibrium to the right, increasing [NaCN] and thus supports the truth of statement E.
  • There is confusion about the presence of ions in the context of the problem, with one participant questioning the relevance of ions mentioned in earlier posts.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the common ion effect and the behavior of [H+] in the solution. There is no consensus on which statement is definitively false, as participants are still exploring the implications of each statement.

Contextual Notes

Participants have not fully resolved the definitions and implications of the common ion effect, nor have they reached a conclusion on the correctness of the statements presented in the homework problem.

JessicaHelena
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Homework Statement



>For a solution that contains 0.10 M HCN and 0.10 M NaCN, which statement is false?
A) This is an example of the common ion effect.
B) The [H+] is larger than it would be if only the HCN was in solution.
C) the [H+] is equal to $K_a$
D) Addition of more NaCN will shift equilibrium to the left
E) Addition of NaOH will increase [CN^-] and decrease [HCN]

Homework Equations

The Attempt at a Solution


I was actually stumped when I first saw the question. I tried wirintg the equation HCN + NaOH --> NaCN + H2O, and made an ice table so to get (0.1 + x)x/(0.1-x), but I wasn't sure where to go after that.
 
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No need for any calculations here, it is about understanding what is going on.

Can you name the acid and the conjugate base? What is ratio of their concentrations?
 
@Borek — The acid is HCN and the conj base NaCN, and the concentrations have ratios of 1:1
 
This is an important special case. You have mentioned various ions. Can you write an equation for the reaction Involving the ions that you have mentioned? Then an expression for the Ka that you have mentioned.
 
@epenguin
I think HCN + NaOH --> H2O + NaCN could work.

then Ka = [H2O][0.10] / [NaOH][0.10] = [H2O]/[NaOH].so,
for (A), I'm not sure what the common ion effect is so I can't say.
(B) I'm not sure what this is talking about. But I think [H+] would be larger when only HCN is in the solution (bc then there won't be any bases like NaOH), if I understand it right, so this looks like it could be false.
(C) I can't say bc of the [NaOH] in the denominator.
(D) yes, by Le Chatelier's principle, so rule this out.
from the equation, for (E), the addition will shift equilibrium to right so [NaCN] increases and the statement is true, so eliminate this.
 
There are no ions in your #5. Yet they appear in #1
 
what do you mean by #5 and #1?
 
Look at the blue strip above this text. This is #8
 
JessicaHelena said:
what do you mean by #5 and #1?

Post number in the thread.
 

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