The student learns that the actual mass percent of iron in the ore sample is greater than the experimental value calculated in part (C). ?
The student claims that the difference between the actual and experimental values could have been caused by rinsing the buret with distilled water just prior to filling it with 0.017MK2Cr2O,(aq). ?
Do you agree with thestudent’s claim?
The Correct Answer and Explanation is :
I disagree with the student’s claim that rinsing the buret with distilled water just prior to filling it with 0.017 M K₂Cr₂O₇(aq) could have caused the difference between the actual and experimental mass percent of iron in the ore sample. Rinsing the buret with distilled water is a standard laboratory practice to remove any residual chemicals from previous experiments, ensuring that the new solution is not contaminated. This procedure does not introduce significant errors into the titration results.
Explanation:
- Purpose of Rinsing with Distilled Water:
Rinsing the buret with distilled water before filling it with the new solution serves to eliminate any remaining chemicals from previous experiments. This step ensures that the new solution is not contaminated, which could otherwise lead to inaccurate measurements. Distilled water is used because it is free from ions and impurities that might interfere with the titration process. - Effect on Titration Results:
The volume of distilled water used for rinsing is minimal and does not significantly affect the concentration of the titrant. After rinsing, the buret is filled with the titrant solution, and any residual water is negligible. Therefore, rinsing with distilled water does not introduce errors into the titration results. - Alternative Rinsing Procedure:
An alternative approach is to rinse the buret with a small amount of the titrant solution before filling it completely. This method ensures that any residual water is replaced with the titrant, maintaining the concentration of the solution. However, this is not always necessary, as the effect of residual water is minimal. - Potential Sources of Error:
If the actual mass percent of iron in the ore sample is greater than the experimental value, other factors are more likely to be responsible. These could include inaccuracies in sample preparation, measurement errors, or issues with the titration procedure itself, such as improper endpoint determination or calculation errors.
In conclusion, rinsing the buret with distilled water just prior to filling it with 0.017 M K₂Cr₂O₇(aq) is a standard and appropriate practice that does not account for the discrepancy between the actual and experimental mass percent of iron in the ore sample. The observed difference is more likely due to other factors unrelated to the rinsing procedure.