Ksp and Q precipitate, Why does volume of water matter

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Discussion Overview

The discussion revolves around the role of water volume in the precipitation of AgCl, particularly in relation to the solubility product constant (Ksp) and the reaction quotient (Q). Participants explore the implications of including water volume in calculations concerning precipitate formation, addressing both theoretical and practical aspects of solubility in aqueous solutions.

Discussion Character

  • Homework-related
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the necessity of including the volume of water in calculations, arguing that since AgCl has low solubility, it should not affect the outcome regarding precipitate formation.
  • Another participant asserts that the reaction quotient (Q) is essential for determining whether a precipitate will form, emphasizing that concentrations, which depend on total volume, are necessary for this calculation.
  • A different viewpoint suggests that if water is added initially, it could prevent precipitate formation due to low concentrations, indicating a potential misunderstanding of the process.
  • Another participant challenges the idea that AgCl would not dissolve, stating that while it has low solubility, it still adheres to Ksp principles and that the final equilibrium state is independent of the order of additions.
  • One participant explains that Ksp represents the ionic product of Ag+ and Cl- concentrations, clarifying that AgCl is not completely insoluble and that the volume of water can influence whether Q is less than Ksp, affecting precipitation outcomes.

Areas of Agreement / Disagreement

Participants express differing views on the importance of water volume in precipitate formation, with no consensus reached on whether it should be included in calculations for AgCl precipitation.

Contextual Notes

Participants highlight various assumptions regarding solubility, the role of water volume, and the conditions under which precipitates form, but these assumptions remain unresolved within the discussion.

AMan24
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Homework Statement


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Homework Equations

The Attempt at a Solution


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So here's my question again, why do you need to include 40L of water in the total volume? It's not like AgCl is going to dissolve in water right? AgCl has low solubility in water. I mean if it was like NaCl then you should include the water because it dissolved, but if it was something that isn't soluble in water at all, then why would you include the water?

Lets say you did a reaction like this and it formed something that isn't solube in water at all, if you include the water in the math, the math will say no precipitate formed, but in reality there will be a precipitate formed.

So for this reaction i'd say a precipitate will form but a small part of it would be dissolved
 
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It is Q that defines what will precipitate and what will not. To calculate Q you need concentrations. How are you going to calculate concentrations without taking the final volume into account?
 
Does it have anything to do with water being added in the beginning? So a precipitate never forms in the first place because the concentrations are too low, if it is then i guess i kind of understand it
 
Why would the situation be different if the water was added later? Why do you think AgCl would not dissolve? It may have low solubility, but it still follows Ksp. Plus, the final equilibrium doesn't depend on the path followed to get to the final state. It sometimes does, when reactions are irreversible, but that's not the case here.
 
what is Ksp of AgCl ?
it is the ionic product of [Ag+ ] and [Cl-] .These are the concentration of ions in solution and solution means solute (AgCl) and solvent( water here).It is not that AgCl is completely insoluble, its very low Ksp indicates that it is very less soluble.It means volume of water added do matter in precipitation of AgCl and cases will be there where Q<Ksp just because of excess water...like in your problem.
 

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