In this assignment you will view several movies showing a chemical reaction. Each movie has several questions designed to focus your attention on concepts to be discussed in lecture. Your complete responses will help me customize my lecture over this material.

Important do not press the enter key or the Return key while you are answering these questions. Your Browser will interpret either key the same as clicking the mouse on the Submit button. So BE CAREFUL!

Name

Lecture Section:

In the next movie we begin with a beaker that was prepared by mixing 5 x 10-5 moles of Fe3+ from an Fe(NO3)3 solution and 2.5 x 10-5 moles of SCN- from a KSCN solution.

Before viewing the movie answer the following questions.

1. Predict the color of the solution in the beaker?

2. After mixing 5 x 10-5 moles of Fe3+ and 2.5 x 10-5 moles of SCN- predict the number of moles of each of the following that is present in the beaker.

a. Fe3+ moles

b. SCN- moles

c. FeSCN2+ moles

Now you may view the movie.

3. In the movie equal samples of the reaction mixture are added to two petri dishes.

To the solution in the petri dish on the left several drops of Fe3+ are added.

Describe what you observe when the Fe3+ is added to the solution in the petri dish.

4. What chemical species must have been formed to account for your observation?

5. What chemical species did the Fe3+, that was added to the solution in the petri dish, react with to produce the change you observed?

6. In the next movie equal samples of the reaction mixture were added to two petri dishes. To the petri dish on the left several drops of Fe3+ have been added.

To the solution in the petri dish on the right several drops of SCN- are added.

Describe what you observe when the SCN- is added to the solution in the petri dish.

7. What chemical species must have been formed to account for your observation?

8. What chemical species did the SCN-, that was added to the solution in the petri dish, react with to produce the change you observed?

9. Briefly, describe any questions/issues you have after watching the two movies on this page.

Or...

How do you explain what happened in the two movies with your predictions in Questions 2a, 2b and 2c above?

10. Using the evidence from your observations in the two movies above, what chemical species are present in the beaker.

In the next movie we will add fluoride ion, F- (NaF) in to the solution remaining in the beaker. Watch the movie and answer the questions below;

11. Describe what you observe when the F- is added to the solution in the beaker.

12. Postulate the chemical species the F- reacted with in the beaker to cause the change you observed.

 

In the next movie the solution the movie above (Q11 and Q12) is poured into two petri dishes. Fe3+ is then added to the petri dish on the left. Play the movie and answer the questions below,

13. Describe what you observe when the Fe3+ is added to the petri dish on the left.

14. What chemical species did the Fe3+, that was added to the solution in the petri dish, react with to produce the change you observed?

 

In the next movie SCN- is then added to the petri dish on the right. Play the movie and answer the questions below,

15. What evidence is there that a reaction took place, or did not take place, when the SCN- is added to the petri dish on the right.

 

 

 

16. What conclusions can you make about what chemical species are present in the solution that was originally in the beaker?

17. With the additional evidence from your observations in the last two movies, again postulate the chemical species the F- reacted with in the beaker.

18. Propose a mechanism that would explain how your answer to Q17 would explain how the addition of F- ion would cause the reddish-brown color of the solution in the beaker to fade/dissappear.