Exam #3 Problem Set (Chemistry)

Please answer the following problems on a separate sheet of paper. As part of the solution, please identify what type of problem each on is (i.e. LODP, % error…)

1) You are working in the lab and are trying to produce salt. You calculate that you should end up with 84g of product, but really you only get 76g. What is your percent error? Brainstorm factors that could have caused you to get less than you expected.

2) If you did an experiment and got a 25% error and our experimental value was 37g, what must have been the accepted value?

3) Assume that you have 43 carbon isotopes with a mass of 12.5u, 18 carbon isotopes with a mass of 14u and another 96 carbon isotopes with a mass of 12.01u. What is the average atomic mass?

4) You find a sample of Calcium isotopes. 22% have a mass of 44u, 18% have a mass of 39u and the remainder have a mass of 40u. What is the average atomic mass?

5) You have Na2Cl4 and an unknown substance with a mass ratio of 0.320. Is your unknown substance Na2Cl4? Please explain your answer thoroughly. Also, please use a % error calculation to justify your answer (how different is your calculated value from the accepted value?)

6) Explain if 918u could be the total atomic mass of sodium in any given substance. Please be detailed in your explanation.

7) You have discovered a compound containing Al and Cl atoms. The Al makes up 20.2% of the substance. The mass ratio of Al to Cl is 0.2535. Write the formula for the substance (The formula should be in the form Al?Cl?). Please show all work and explain your method for solving the problem. Please attempt this problem, as partial credit is available.

8) Write a problem that is similar to the isotopic penny lab. Use your other problems as examples. Please include the solution!

9) If you were in the 9 energy level (assume that it exists), how many electrons could fit in it? If you discovered an energy level that could hold a maximum of 1849 electrons, what mythical energy level would it be?

10) Please draw Bohr models for elements 1-21 (you’ve done most of these…I just want to make sure that you’ve got it.)

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