Science Buddies: "Ask an Expert"

Dear Expert,

I am learning that the basic reaction in the dulling of copper in pennies to copper oxide is:
2Cu + O2 goes to 2CuO (copper is oxidized from Cu to Cu II).

I'm trying to understand the reactions involved in the copper test tablet. Can you tell me what the reaction is for the following?

1) copper test tablet with water to form water control
2) copper test tablet with vinegar to form vinegar control (and what if I use vinegar + salt?)
3) copper test tablet with the solutions after cleaning pennies (both in water and in vinegar, and vinegar + salt)

What are the chemicals in the reaction that are making the color change? What is the chemical that makes the reddish-orange color? I read somewhere that it is a form of copper (1) oxide.

Thanks,
EFL

Hi,

Sorry no one answered your questions. I will try to help you.

Your first question about the three conditions:

1. Cu tablet + water is a Control to show that there is no copper ions in your water. It is unlikely, but copper pipes can leach out copper and this could show up if you used tap water for the experiment.

2. Cu tablet + vinegar is another control to show that the vinegar contains no copper. Again, household vinegar should contain no copper. Also, the salt should not contain Cu, but you could do another control with a salt solution if you wanted to be positive.

3. Cu tablet + water from cleaning the penny. This should contain copper ions from the CuO that was dissolved by the acetic acid in the vinegar.


For your last question i did a search for copper test kits and found a lot but no information on the specific chemical reaction that causes the color change: http://www.amazon.com/s?rh=n%3A12729770 ... 3764070011

The Materials part of the Scibuddies project guide does not say where the test tablets come from, but I can try to find out. Was there any information in your kit as to the manufacturer of the tablets? If you could find the name of the company that makes them, you could call and ask them what is in the tablets.

I hope this helps.

Sybee

Thanks for your feedback,
I would like to know if any generic copper test tablets will work. I'm in the phase of gathering materials currently. Right now the copper test kit on this science buddies website is out of stock, and I'm wondering if any other
will work.

Thanks
EFL

EFL - The kit in the Science Buddies Store should be available again by the end of next week. If your timing is such that you need to do your project without the kit, I can possibly direct you to an alternate solution. Please let me know, and I will follow up with you.

Amy
Science Buddies