Why do unexpected precipitates form in precipitation reactions?

In summary, test tubes can be affected by age, temperature, and other factors which can affect the outcome of precipitation reactions.
  • #1
danago
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Hi. If i was to conduct a few precipitation reactions, is there any reason why an unexpected precipitate will form, or any reason an expected precipitate will not be formed? I've though about things such as added ions in tap water (chlorine etc). Any other things?
 
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  • #2
danago said:
Hi. If i was to conduct a few precipitation reactions, is there any reason why an unexpected precipitate will form, or any reason an expected precipitate will not be formed? I've though about things such as added ions in tap water (chlorine etc). Any other things?
Perhaps the test tubes were not cleaned properly and some ions from the previous experiment were left behind. Maybe there was nothing wrong and it was the lab technicans fault for incorrectly labeling the bottles containing the substances.
 
  • #3
pavadrin said:
Perhaps the test tubes were not cleaned properly and some ions from the previous experiment were left behind. Maybe there was nothing wrong and it was the lab technicans fault for incorrectly labeling the bottles containing the substances.

lol :rofl:
 
  • #4
Some precipitation reactions are very sensative to temperature and some, like the silver mirror experiment, require rough surfaces or some point to start precipitating from (seed).

I have had such test fail or succeed just on the basis of the age of the test tube, with better results in older (scratched) glass tubes than in out-of-the-box tubes that are smooth.
 
  • #5
danago said:
Hi. If i was to conduct a few precipitation reactions, is there any reason why an unexpected precipitate will form, or any reason an expected precipitate will not be formed? I've though about things such as added ions in tap water (chlorine etc). Any other things?

Yes, that as well as other factors e.g. coprecipitation etc...precipitation isn't so simple as adding the components. Unless carefully devised the precipitated product may be more or less crude. Since this is probably for general chemistry you won't have to worry about the analytical aspects too much, but in actuality the process is drawn out. In your case, I would consider the solubility of the particular precipitate, so as to account for the volume of solvent needed, you want to be well over the point of saturation to see the solids. Also, consider the temperature, you may need to heat the solution to digest sample and then cool it down to a certain temperature; that is sometimes it's preferable to employ an ice bath.
 
  • #6
Thanks for the help everyone :)
 

1. What is a precipitation reaction?

A precipitation reaction is a type of chemical reaction in which two soluble substances form an insoluble product known as a precipitate. This occurs when the product has a lower solubility than the reactants, causing it to separate and form a solid.

2. How do you know if a precipitation reaction has occurred?

A precipitation reaction can be identified by the formation of a cloudy or milky appearance in the solution, indicating the presence of a precipitate. This can also be confirmed by performing a simple filtration test, where the precipitate is separated from the remaining solution.

3. What factors affect the outcome of a precipitation reaction?

The solubility of the reactants, temperature, and concentration of the solution all play a role in the outcome of a precipitation reaction. Solutions with higher concentrations or higher temperatures can increase the likelihood of a reaction occurring, while solubility determines whether a precipitate will form.

4. Can a precipitation reaction be reversed?

In most cases, a precipitation reaction is irreversible. Once a precipitate has formed, it is difficult to dissolve back into the solution. However, there are some exceptions, such as using acid or heat to dissolve the precipitate.

5. What are some real-life applications of precipitation reactions?

Precipitation reactions have several practical applications, including water treatment, pharmaceutical manufacturing, and mineral extraction. In water treatment, precipitation reactions are used to remove impurities and contaminants from water. In pharmaceutical manufacturing, they are used to purify and isolate specific compounds. In mineral extraction, precipitation reactions are used to extract valuable metals from ores.

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