What Could Cause Errors in Barium Sulfate Precipitation?

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Discussion Overview

The discussion revolves around potential sources of error in the precipitation of barium sulfate during a laboratory experiment aimed at determining sulfate content in lawn fertilizer. The focus includes practical aspects of the experiment, such as the dissolution process, washing of precipitates, and the impact of impurities on results.

Discussion Character

  • Experimental/applied
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that their results were about 2% lower than expected and questions whether impurities could lead to a lower mass of barium sulfate precipitate.
  • Another participant asks for clarification on the washing process of fine solids like barium sulfate.
  • A participant inquires if all fertilizer was dissolved and whether the precipitate was aged before filtering, suggesting that impurities typically lead to higher results, not lower.
  • A participant mentions that some precipitate got stuck to the bottom and questions if washing with large amounts of de-ionized water could have caused peptization or loss of precipitate without cloudiness in the filtrate.
  • One participant warns that washing with excessive water risks dissolving some of the precipitate and suggests using a solution containing the ion used for precipitation instead.
  • Another participant points out that barium sulfate is considered insoluble in water, prompting a discussion about the concept of solubility.
  • A later reply challenges the notion of "insoluble," stating that there are varying degrees of solubility and references the solubility product.

Areas of Agreement / Disagreement

Participants express differing views on the impact of impurities and washing methods on the results, with no consensus reached regarding the sources of error in the experiment.

Contextual Notes

There are unresolved questions about the effects of washing techniques on precipitate loss and the implications of impurities on mass measurements. The discussion also touches on the definitions and nuances of solubility, which may affect interpretations of the results.

ASidd
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Precipitation of barium sulfate??

We had to determine the content of sulfate found in lawn food for a class prac.

Anyway what we did was to dissolve the fertilizer in HCl and then add barium cholride to it in order to precipitate sulfate as barium sulfate. We later determined its concentration using gravimetric analysis.

The results of my group was substantially different to the actual amount of sulfate present in the fertilizer. Our result was about 2% less than the actual value.

Now I am trying to find some possible sources of error in the prac. I know that we spilled a couple of drops of the mixture but it was not that much. I was wondering if somehow impurities can impact upon the mass being less than it's supposed to be? I know impurities usually cause mass to be larger but I read somewhere that occulsions can causesul mass to be smaller than the actual value?

Is this true?
 
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Also can someone tell me what is the meaning of washing the precipitate. Like with such a fine solid like Barium sulfate how would you wash it?
 


Was all fertilizer dissolved, or was there some solid residue?

Have you aged the precipitate before filtering?

Most impurities will mean your final result would be too high, not too low.
 


No all of the fertilizer had definitely dissolved

We did let the precipitate sit for about 48 hours but what happened was that some of it got stuck to the bottom so we had to wash it with about 2 bottles of DE-ionized water in order to make it unstuck. So I am wondering if some of the precipitate peptized upon adding the huge amounts of de-ionised water?
Although when we filtered the solution the filtrate didn't look cloudy but I am also thinking if some of the precipitate went through without the filtrate becoming cloudy?
 


If you wash with copious amounts of water yo always risk dissolving some of the precipitate. It is better to wash with solution containing ion used for precipitation.
 


But barium sulfate is insoluble in water?
 


There is no such thing as "insoluble". There are varying degrees of solubility.

Google for "solubility product".
 

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