Why the experimental error for CaOH is larger than MgO?

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SUMMARY

The discussion centers on the larger experimental error observed for calcium hydroxide (Ca(OH)2) compared to magnesium oxide (MgO) during a lab experiment applying Hess's law. The primary reason identified is the assumption that all calcium hydroxide formed remained in solid form, while some dissolved, affecting the heat of formation calculations. The participant seeks clarification on how to calculate the impact of this assumption and expresses confusion regarding the concept of partial hydrolysis, which has not been covered in their coursework.

PREREQUISITES
  • Understanding of Hess's law and its application in thermochemistry.
  • Knowledge of heat of formation calculations.
  • Familiarity with the dissolution process of ionic compounds in water.
  • Basic concepts of hydrolysis in chemistry.
NEXT STEPS
  • Research the concept of partial hydrolysis and its implications in thermochemical experiments.
  • Study the calculation methods for heat of formation, specifically for ionic compounds like Ca(OH)2.
  • Explore the differences in solubility and dissociation between MgO and Ca(OH)2 in aqueous solutions.
  • Review experimental error analysis techniques in chemical experiments.
USEFUL FOR

Chemistry students, laboratory technicians, and educators involved in thermochemistry and experimental design, particularly those focusing on heat of formation and solubility issues.

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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