Why is my solution precipitating after neutralization with NaOH and HCl?

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Discussion Overview

The discussion revolves around the unexpected precipitation occurring after neutralization of hydrochloric acid (HCl) and sodium hydroxide (NaOH) in a solution intended for measuring the immunogenic effects of a molecule. Participants explore potential causes for this phenomenon, including contamination and chemical interactions, within the context of basic chemistry principles.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes the experimental setup and notes massive precipitation after neutralization, expressing confusion given the expected solubility of sodium chloride.
  • Another participant suggests that contamination in the solutions could be responsible for the precipitation, emphasizing that a neutralized solution of HCl and NaOH should be homogeneous.
  • A later reply proposes that the precipitation may be due to metal cation impurities in the NaOH solution, which could be precipitating out upon neutralization.
  • One participant mentions that experimentation indicates the NaOH solution was contaminated, raising questions about the source of this contamination.
  • Another participant speculates that the contamination could be related to the storage of NaOH in "soft glass," suggesting a possible rediscovery of silica solubility in basic conditions.

Areas of Agreement / Disagreement

Participants express differing views on the cause of the precipitation, with some attributing it to contamination while others suggest potential chemical interactions. The discussion remains unresolved regarding the exact source of the precipitation.

Contextual Notes

Participants note the importance of solution purity and the potential effects of storage materials on chemical behavior, but do not resolve the specific conditions leading to precipitation.

Who May Find This Useful

Researchers and students involved in chemistry experiments, particularly those studying solution chemistry and the effects of contaminants on chemical reactions.

Nix13
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We're attempting to measure the immunogenic affects of a particular molecule after subsequent acid and base treatments. As a first version, we're keeping it simple. After all treatment and neutralization, we wind up with 400 uL 0.2 N HCl + 400 uL 0.2 N NaOH + 200 uL H2O. We are getting massive precipitation upon neutralization! To test whether this was due to our compound, I did a water control and the same thing happened. Considering the solubility of NaCl is in excess of 6 M, what the hell could be going on? Any ideas would be greatly appreciated. This is basic gen chem stuff, so I am baffled.
 
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Nix13 said:
We're attempting to measure the immunogenic affects of a particular molecule after subsequent acid and base treatments. As a first version, we're keeping it simple. After all treatment and neutralization, we wind up with 400 uL 0.2 N HCl + 400 uL 0.2 N NaOH + 200 uL H2O. We are getting massive precipitation upon neutralization! To test whether this was due to our compound, I did a water control and the same thing happened. Considering the solubility of NaCl is in excess of 6 M, what the hell could be going on? Any ideas would be greatly appreciated. This is basic gen chem stuff, so I am baffled.

You have contamination in your solutions if you are seeing precipitation with "pure water". The end-point of a titration of HCl with an equal amount of sodium hydroxide is a sodium chloride solution, which is a homogeneous liquid.

Assuming that your precipitation is with hydroxide, you likely have some kind of metal cation impurity that is precipitating out.

http://cpe.njit.edu/dlnotes/che685/cls06-2.pdf
 
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Quantum Defect said:
You have contamination in your solutions if you are seeing precipitation with "pure water". The end-point of a titration of HCl with an equal amount of sodium hydroxide is a sodium chloride solution, which is a homogeneous liquid.

Assuming that your precipitation is with hydroxide, you likely have some kind of metal cation impurity that is precipitating out.

http://cpe.njit.edu/dlnotes/che685/cls06-2.pdf

With some experimentation it appears our NaOH solution was contaminated, though how and by what I am puzzled, since the precipitation filled as much as half the volume.
 
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Nix13 said:
NaOH solution was contaminated ... as much as half the volume.
Stored in "soft glass" for any length of time? Sounds like a rediscovery of silica solubility in base.
 
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