07/03/08

Next week's experiment is going to be a long one. Brace yourselves!
I have posted a grade calculator Excel spreadsheet on this website (under Grading) that will help you calculate your current standing in this class.

Report 4. Do not forget to include a sample of each type of the calculation performed in the report. Include a sample calculation for each data table that you have (three total). Show a sample for one trial only. You DO NOT have to show a sample calculation for any of the average or standard deviation calculations.
Remember, you have to have knowledge of the "true value" to be able to evaluate the accuracy of your results. The precision, however, is evaluated in terms of the standard deviation values. The smaller the standard deviation is relative to the average, the more precise is your result.

Post-lab 4, question 4. In this problem, you have two chemical reactions, in which hydrochloric acid is consumed. Solve this problem individually for each reaction, then add up the results.

Pre-lab 5, question 2. In the molecular formula of Fe(NH₄)₂(SO₄)₂·6H₂O, the six waters at the end are the so called "waters of hydration". By definition, waters of hydration are the water molecules that are part of the crystalline structure of the compound and are present in a fixed molar ratio compared to the number of moles of the compound itself. To calculate the molecular weight of the hydrated compound, you need to add the mass of the waters of hydration to the mass of the compound itself.

06/26/08

Report 3. In the Discussion, you have to provide 15 balanced molecular and 15 net ionic equations for the 15 precipitates that you observed in the lab (30 reactions total). That does not include the five "false positives": Na₂S + acids, Na₂S + Ba(NO₃)₂, and NaOH + Ba(NO₃)₂.

Post-lab 3, question 4. You have two reagent bottles with two different aqueous solutions. One contains Na₂SO₄ (aq), the other - AgClO₃ (aq). The bottles are not labeled, so you don't know which one is which. You need to suggest a qualitative chemical test that would help you label these bottles. To solve this problem, you can choose to selectively form a precipitate in the Na₂SO₄ solution (but not in the AgClO₃ solution) by adding a specific reagent to both.
For example, if you add a Ba(NO₃)₂ (aq) solution to both reagent bottles, you will see a precipitate formation in the bottle that contains Na₂SO₄ (aq) due to the  formation of BaSO₄ (s). No visible change will be observed in the AgClO₃ solution. You can also choose to selectively form a precipitate of AgCl in the AgClO₃ solution (and not in the Na₂SO₄) by adding  the NaCl (aq) reagent to both. Use Appendix 2 for reference.

06/19/08

Report 2. All of the calculations for this lab can be easily done in Excel, so go ahead and use it. If you do not know how to use Excel, here is a link to a tutorial that can help you get started:
http://www.ischool.utexas.edu/technology/tutorials/office/excel/.
Calculate the averages and the standard deviations for the percentages only, not for the masses (be sure to report them using the correct number of significant figures).
Apply the Q-test (if necessary) to the individual sets of data for:
1) percent of NaCl in the mixture
2) percent of SiO₂ in the mixture
3) percent of CaCO₃ in the mixture
If you do use the Q-test to identify your outliers, you have to show your work (include it into your report under Sample Calculations).
There is no need to apply the Q-test to the total percent recovery data set. If you find an outlier in an individual set of data for either of the components, you can exclude the corresponding total percent recovery from the average and the standard deviation calculations.
Sample Report for Experiment 2 is posted on this website under Sample Report.

Quiz 1. We are going to have our first quiz next week. This first quiz will be on the material of Experiments 1 and 2. To prepare, you need to concentrate on the following:
1) Learn the definitions for all the terms introduced in class (see lecture notes)
2) Understand your experimental procedure (see lecture notes, pre-lab questions, and discussion questions)
3) Understand how to do post-lab type problems (see post-lab questions).

06/12/08

The following assignments are due next week: Report for Experiment 1 (for reference, see Sample Report 1 posted on this website under Sample Report), Post-lab for Experiment 1 (from the hand-out), and Pre-lab for Experiment 2 (from the manual). All of the assignments have to be hand-written in your laboratory notebook. Start every new assignment on a new page, so that you can easily tear out corresponding copy pages and submit them to your TA for grading.

Sample Preliminary Write-up for Experiment 2 is posted on this website under Sample Report. Have yours done before coming to class. And remember, you do not have to turn it in this week. Rather you will work with it, finish it up, and turn it in to your TA for grading next week as your Report 2.

Make sure you dress appropriately next time you come to class. Starting next week, we will be enforcing the laboratory dress code. See syllabus for details.

Report 1. Make sure you use the correct number of significant figures when you report your results as Average ± Standard Deviation in your first report. To be able to evaluate the accuracy of your measurement, you need to compare it to the "true value" (best estimate). In the first approximation, you can use density of water as a point of reference for the density of Diet Coke. A can of Coke states that it has 39 g of sugar as high fructose corn syrup and/or sucrose in 355 ml of soda. That means that Coke is an 11% by weight sugar  solution. The densities of the 11% fructose and sucrose aqueous solutions are 1.0427 g/cm³ and 1.0423 g/cm³ at 20 °C, respectively.

06/04/2008

Our first day of class is Tuesday (June 10th) for unique ## 91780-91800 and Wednesday (June 11th) for unique ## 91805-91825. We will start with the experimental work right away. You will get a print-out of the experimental procedure in class.

For the class, you will need a Lab Manual (Summer 2008 edition, available at the University Co-op), a bound Laboratory Notebook with duplicate numbered pages (sold by the University Co-op or UT Copy Center @ WEL2.228), and a Combination Lock. Note, that you will not need your lab manual for the first day of class. Please bring a combination lock.