3/16 Chemistry update and homework due 3/23

Hi folks,

Today we went a bit deeper into the realm of redox reactions and took a look at electrochemistry.  We did another lab this week where I asked the students to explore electrodes and electrolytes to see which ones created the greatest voltage.

For homework this week:

Read pages 337 to 357

And:

For the usual 10 points, do all of the questions marked with an "*".  If you would like some extra credit points, however, do some of the four unmarked questions.  Also, feel free (in fact I expect you to) to use the internet and/or the book to do some research for the answers for these.  The more details and the more work it appears that you did to answer the questions, the more extra credit points I'll award.  There are 10 possible extra credit points available.

Some helpful facts:

"silver" coins are coated in nickel

Paper clips are coated in zinc

Spoons are coated in Chromium Oxide

Vinegar is usually a 5% solution of acetic acid CH3COOH

Baking soda NaHCO3

Ammonia is NH4

Dr. Pepper is Phosphoric acid H3PO4

1.  Does the amount of electrolyte matter?  How do you know?

2.  Does the amount of electrodes matter?  How do you know

3.  Any clue as to why the voltage sometime positive and sometimes negative?

4.  Did you get different results with clean vs. dirty electrodes?

* 5.  What appeared to be the most effective electrolyte? What is your evidence?

* 6.  What appeared to be the best pair of electrodes? What is your evidence?

7.  Any thoughts as to what is a good electron giver vs. an electron taker?

* 8.  Did any liquids not work as an electrolyte?  What is your evidence?  Why didn't it work?

* 9. Draw a picture of one of your more successful set ups.  Label the electrodes and the electrolyte.  What are the ions? Show me what the movement of metal ions are.  Would one of the electrodes get plated (covered in atoms) if you let the set up continue to run?  What ions make up the electrolyte?

* 10.  Pick three electrolytes that you used.  What are the ions in each one?

Now let's look at the experiment from the last class.  

*11.  Write the formula for your best guess for three of the reactions that you saw.

*12.  Create half reactions for each of the three reactions you wrote in question 11.