Common Titration Errors and How They Can Affect Results

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Discussion Overview

The discussion revolves around the potential errors encountered during a titration lab aimed at determining the weight percent of carbonate ions in a sample containing NaCl and CaCO3. Participants explore various sources of error that could lead to discrepancies in results across multiple titrations, focusing on issues related to solution preparation and measurement accuracy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant notes a significant difference (~10%) in results between two titrations and speculates on possible errors, including inaccurate buret readings and improper mixing of diluted HCl and NaOH solutions.
  • Another participant questions the volume of titrant used and suggests that a misreading of the buret would need to be substantial to account for the observed error.
  • A participant expresses confusion regarding the assumption that the solutions used in both titrations were identical and asks for clarification.
  • Another participant mentions that the amount of unknown used was nearly identical between replicates, suggesting that the volume of HCl used might be a source of error.
  • Further inquiry is made about the physical characteristics of the solid material used and the titration endpoint, including the color of the solution and the indicator employed.
  • Clarification is sought on the assumption of identical concentrations of HCl and NaOH in both replicates, with a focus on the likelihood of insufficient mixing affecting results.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the sources of error, but there is no consensus on which specific factors are most significant or how they interact. The discussion remains unresolved with multiple competing views on the causes of the discrepancies.

Contextual Notes

Participants acknowledge potential limitations in the accuracy of measurements and the preparation of solutions, but specific assumptions and the extent of their impact on results are not fully explored.

higherme
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I did a titration lab to find out the weight percent of CO3^2- in an unknown sample which contains only NaCL and CaCO3^2-.

My results were about 29% for the first titration and 18% for the second titration; I was wondering the types of error that led to this ~10% difference.

Some of the errors I thought of are:
- The buret readings were not very accurate.
- When preparing the 1 L of 0.01M HCl from 6M HCl (dilution) the 6M HCl was not mixed well with water. (used to dissolve the unknown)
- Same for the 1L of 0.01M NaOH from 6M NaOH which was used to titrate the unknown
 
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What volume of titrant did you use? I'll assume roughly 20 mL. You would have to misread the buret by 2 mL for this to be the source of your error.

- When preparing the 1 L of 0.01M HCl from 6M HCl (dilution) the 6M HCl was not mixed well with water. (used to dissolve the unknown)
The poor preparation of the HCl would give you an error of accuracy, not precision. This problem deals with an error of precision.

Why don't you assume that the solutions you used in both replicates was identical. What could have caused you this error under that assumption?
 
"Why don't you assume that the solutions you used in both replicates was identical. What could have caused you this error under that assumption?"

i don't get what is meant here~
 
well the amount of unknown i used for both replicates were pretty much around the same weight... just 0.001g difference... would that matter?

well... the amount of HCl used to dissolve the first sample is 21.31ml and 25.47ml for the second sample... maybe the error is there??

is that kind of right?? :P
 
Describe the solid material you used (NaCl + CaCO3). Was it a fine powder or were there larger grains apparent? Describe your titration endpoint. Were both replicates identical in color. Was the color dark or light? What indicator did you use?
 
higherme said:
"Why don't you assume that the solutions you used in both replicates was identical. What could have caused you this error under that assumption?"

i don't get what is meant here~

I meant that you should assume that the concentration of HCl used in both replicates was identical and that the concentration of NaOH used in both replicates was identical. Insufficient mixing when diluting these reagents is possible but how likely is it? Did you at least try to mix the individual solutions?
 

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