Questions:

1. In this lab, we used successive heating, a cyclic process of heating, cooling, and weighing.
   1. What is the purpose of this process?
   2. When do we stop the cycle?
   3. In the lab, if you skipped the successive heating step, how would this affect your results? Explain.
   4. You are working on your first appointment in a research lab on campus, and you are tasked with using successive heating in part of your procedure. You get the following data:

You want to impress your research advisor and get the best result possible. What should you do: heat the sample again or stop the heating cycles and use the mass from the 3rd heating in your calculations. Explain the reasoning for your choice.

1. Think about how error would affect the results of this week’s experiment. Imagine if a TA did not add enough HCl in Part 1, step 3 , so there was unreacted NaHCO3 left in the evaporating dish when the TA heats the sample. How will this error affect the percent yield of NaCl for the reaction? Explain your reasoning.

1. Dr. H collects the following data for Part 2 for a student who is making up the lab. The student completes the calculations (see note below) and hands in the lab, but the student indicates their confusion about the calculated percent yield. There are three errors in these calculations. Identify the errors and provide feedback to the student about how to perform the calculations correctly.

[Not real student work – Dr. H made a simulation of the most common mistakes.]

1. Apply what you have learned: Dr. H is making solid alum (KAl(SO4)2•12H2O) in the lab from aluminum cans that she has in her office. She starts with 10.000 grams of solid aluminum and all other reagents in excess. The overall reaction for this synthesis is:

2Al(s) + 2KOH(aq) + 10H2O(l) + 4H2SO4(aq) ? 2KAl(SO4)2•12H2O(s) + 3H2(g)

1. Calculate the theoretical yield of Dr. H’s synthesis. Report it with the correct number of significant figures and the appropriate units. SHOW ALL YOUR WORK.

1. If Dr. H isolates 53.795 g of alum at the end of the synthesis, what is the percent yield for this reaction?