Why the experimental error for CaOH is larger than MgO?

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Discussion Overview

The discussion revolves around the experimental error associated with the heat of formation calculations for calcium hydroxide (Ca(OH)2) compared to magnesium oxide (MgO) in a lab context applying Hess's law. Participants explore the reasons behind the larger experimental error for calcium hydroxide, including assumptions made during the experiment.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the assumption of solid calcium hydroxide may not hold true, as some of it could have dissolved, impacting the heat of formation calculations.
  • Another participant suggests that the discrepancy in experimental error could be accounted for by considering partial hydrolysis of calcium hydroxide.
  • A participant expresses confusion regarding the term "partial hydrolysis," indicating it has not been covered in their class.
  • Concerns are raised about the clarity of the problem statement, particularly regarding the notation of calcium hydroxide and the phrasing of the question, which may affect the understanding of the issue.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the clarity of the problem or the implications of the assumptions made in the experiment. Multiple viewpoints regarding the causes of the larger experimental error remain present.

Contextual Notes

There are indications of missing assumptions regarding the behavior of calcium hydroxide in solution and the potential effects of hydrolysis on the experimental results. The notation used for calcium hydroxide may also lead to misunderstandings.

Who May Find This Useful

This discussion may be useful for students engaged in chemistry experiments involving Hess's law, particularly those exploring the heat of formation and the implications of solubility and hydrolysis in their calculations.

Alpha123
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Homework Statement



I did a lab on the experimental application of Hess's law. There were two experiments where a substance in a solution was dissolved and the temperatures were recorded. Then the standard heat of formation for the substance was calculated. The first experiment used MgO and HCL and the second experiment used CaOH and water.

A question in the lab was :

"Explain why the experimental error for the calcium error for the calcium hydroxide is much larger than magnesium oxide.In this experiment, it was assumed that the calcium hydroxide formed was in the solid form, whereas some of the solid that formed must have dissolved. Using this information, determine by calculation how much of an impact the above assumption had on the final experimental value for the heat of formation of calcium hydroxide."

I don't quite understand what calculation to do here, or an explanation for this either. It cannot be the percentage error as i have already calculated those in an earlier question. Any help on this question would be very much appreciated, thank you.
 
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Can you account for the discrepancy with an assumption of partial hydrolysis?
 
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I don't know what that means, we haven't learned it in class.
 
Sounds cryptic to me.

But to be honest - your post starts with CaOH instead of Ca(OH)2 and contains statements like

Alpha123 said:
the experimental error for the calcium error for the calcium hydroxide

so I am not convinced the problem is correctly represented.
 

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