Science Buddies: "Ask an Expert"

Ok so we are doing this assignment for school and i need some help

the assignment is testing if the law of conservation of matter is true
matter cannot be created or destroyed is what is meant
so we are seeing if mass is the same at beginning, as the end mass.

we had two samples of copper and put them into nitric acid but then each sample went through different chemicals but in the end they both formed copper oxide.

the experiment diagram is shown below : CU->CuNO3-> 1.CuOH->CuO (black)
2.CuCO3->CuCO3 (CuO)

sry but im a bit confused about why we made copper nitrate- was it to make a solution/ disolve the copper = change to test if even though the copper was changed form the mass is still the same? am i right?

in the first sample (1.) above , sodium hydroxide NaOH was added to CuNO3 to get CuOH forming a solid (precipitate)->filtered leaving solid inside-> then burnt it inside a crucible to get rid of filter paper and only have the mass of the solid. Anyways what is this solid? i dont understand the change from CuOH to CuO

also in step 2. sodium carbonate was added to get CuCO3 but took several more steps to arrive to copper oxide...
basically i dont get how we get copper oxide and
Why are we trying to get to copper oxide?

could you possibly break down what is meant in each step and why it was done in simple terms. I have ideas but im not sure if they are correct

also if it is not much trouble could you possibly post any internet sites/ resources that may help me to understand the experiment
or give me any clues on the topics i should research

thank you so much! i hope i get answers soon before my assignment is due

Hello,

I don't have the answer to your question, but I would suggest that you would post in the physical science section of the forum, where people will be more qualified to answer chemistry problems.

I hope this helps a little bit!

Heloise

Hello:
I moved your post to Grades 9-12 Physical Sciences so that an expert can find and answer your questions.
Ketih

Hi Cheese123,

Welcome to Science Buddies!

This is essentially a quantitative analysis experiment. I don’t think there is an experiment like this on the Science Buddies website, but it is an excellent project to demonstrate the law of conservation of matter. The point of this experiment is to show that you have the same amount of copper at the beginning and end of the experiment. You can compare quantities of the copper at the beginning and end of the experiment if you know how to convert to grams of copper to moles of copper. A mole of an atom is equal to 6.23 x 10 23 atoms.

Here is some information to help you get started on the project write up. The formula weight of copper is 63.43 grams per mole, so you will multiply the grams of copper that you started with by (1 mole and divide by 63.54 grams) to calculate the number of moles of copper that you started with. Copper II oxide (CuO) has a formula weight of 79.545 grams/mole so you would multiply grams of the black power by 1/79.545 to calculate moles of CuO. Hopefully you will show that the moles at the beginning and end of the experiment are the same, so you didn't lose or gain any copper.

The nitric acid was used to dissolve the copper. The Wikipedia article on copper II nitrate includes the formula to dissolving copper metal in nitric acid and also the formula for the conversion of copper nitrate to CuO when the copper II nitrate is heated to 180 degrees Centigrade. The NaOH precipitated the Cu as CuOH2and heating the CuOH2 n the crucible drives off the hydrogen, leaving CuO.

http://en.wikipedia.org/wiki/Copper(II)_nitrate

It sounds like the second part of the experiment started with copper carbonate, CuCO3. When this molecule is heated at 290 degrees Centigrade, carbon dioxide (CO2) is released into the atmosphere, leaving copper II oxide (CuO). The Wikipedia article includes the formula for this reaction.

http://en.wikipedia.org/wiki/Copper(II)_carbonate

Does this help? Do you have any questions?


Donna Hardy

thank you donna that helped a bit more - i did some more research and discovered more about my experiment now all i have to do is try to convert grams of copper to moles to compare right? i got the start weight of the copper was 1.04g and 1.05g and end weights of CuO was 1.81g and 7.6g- there must have been an error in our experiment somewhere

thanks again!
sorry for the late reply

Hi Cheese 123,

Yes, you are correct; you just have to convert grams of copper, copper oxide, or copper carbonate to moles of copper to compare quantities.

Were the results you posted for the conversion of copper metal to copper II oxide? What about the part of the experiment that started with calcium carbonate? If I have understood your data, then 1.04 and 1.05 grams of copper metal are .01636 and .0165 moles of copper, respectively. And, 1.81 grams of CuO is .022 moles and 7.6 grams is .095 moles. The first result is pretty good, but you definitely made some sort of experimental error on the second result. Do you have any idea what happened? Did you tare the balance?

I see your project is due on Tuesday. Do you have any last minute questions?

Donna Hardy