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Attachment | Size |
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Tungstosilicic acid lab VIPEr.doc | 294 KB |
RH H4SiW12O40.txt | 998.27 KB |
RH H4SiW12O40 TGA.xls | 998 KB |
RH tungstosilicic acid titration.xls | 23.5 KB |
A student performing this experiment should:
1. gain proficiency in chemical synthesis;
2. use error propagation methods to state titration results with an appropriate uncertainty; and
3. interpret TGA data for dehydration.
Jolly's synthesis, while reliable, yields 32 g of product, which is more than enough. I scaled back the quantities used to 25% of what was called for. Students should expect a yield of 8 g.
I purposely added in the error propagation as a connection to the analytical chemistry course that all students had previously taken. This could be omitted if your students have not had this preparation. If you do the error analysis, you will need to standardize the NaOH and report its concentration with uncertainty, so that students can use this in their calculations. Sample titration calculations and results are included in the Excel file.
If time permits and you are so inclined, you could acquire a TGA profile for each student's sample. In this experiment, they should all be about the same and obtaining a profile for each was deemed to be a waste of resources. Therefore, I instead demonstrated the sample prep and operation of the instrument to the students and used the same data for the entire class. If you do not have access to a TGA, I have attached a text file of the raw data which you can use to generate the TGA profile (plot). The data begins on about line 40, after all the instrument parameters. Columns two and three contain the pertinent data of temperature and mass, respectively. A second Excel file contains the worked up TGA data and the plot.
Due to the drying period, this lab is conducted over two weeks. However, neither week's activities completely use allocated time. You could maximize efficiency by having students work on some aspect of a different lab experiment during one or both weeks.
Dar Sir/Madam,
I would like to know how to determinte the percentage yield of the product. As the equaton is unbalanced, how can you calculate the percenage yield? Can you show me the steps to calculate?
Best Regards
Wong TM