2CuO + C -> Something else than 2Cu + CO2

[mertzi]

Hello! I really hope I get my post right this time because if not the rules are really hard to understand.

1. Homework Statement
We did a lab the other day where copper(II)oxide reacts with carbon (charcoal powder) when adding heat from a bunsen burner. Our experiment was a success but I'm struggling with what our teacher said afterwards; that there can be two different reactions where two different solids form. We studied the product/products afterwards under a loupe and you could clearly see pure copper but also a lot of black solid something attached to the copper and it didn't look like charcoal because there were a small amount of leftovers which clearly looked like small pieces of charcoal, also they weren't attached to the copper. But according to the chemical equation the carbon should be excessive, does the charcoal carbon transform into some other form of carbon (besides the CO₂)?

Homework Equations

First reaction:
2CuO + C → 2Cu + CO₂
This one I understand completely, this is called single replacement I think?

The molar ratio is 2:1:2:1

amount of substances:
n_CuO = 0,025 moles
n_C = 0,021 moles

C is excessive which means the theoretical exchange is 0,025 moles Cu and 0,0125 moles CO₂, is this correct? Unfortunately we didn't think of weighing the product, the lab mainly was about collecting the CO₂ and calculating the exchange percentage of real exchange divided by theoretical exchange.

The Attempt at a Solution

I understand this is completely wrong but the rules have to be obeyed so here is my wild hypothesis for the second reaction:
CuO + C + O₂ → CuCO₃
I know this is copper(II) carbonate and it should be green and it doesn't form from combustion but that's the only other reaction I can think of from the reactants.

 

[DrDu]

Do you know other oxides of copper and carbon?

 

[mertzi]

I think so but the only other elements I can think of that can take part of the reaction is nitrogen or water from the air.

 

[DrDu]

What do you mean with "you think so"? Are there other oxides or not?

 

[mertzi]

What do you mean with "you think so"? Are there other oxides or not?

Yes, I know other oxides like iron oxide, aluminium oxide etc. Do you mean I should post all oxides I can think of? I'm sorry to say that it's not encouraging to be met with such condescension.

 

[DrDu]

No, I said other oxides of copper and carbon.

 

[mertzi]

Carbon monoxide and carbon trioxide but those are not solids. Also Cu₂O and Cu₂O₃ but these are still copper oxides? I'm sorry I've been reasoning here for 20 minutes but I really get nowhere.

 

[DrDu]

I never heard of carbon trioxide, but you should take a closer look at carbon monoxide. What would happen if most of the carbon did not react to the dioxide but the monoxide?

 

[mertzi]

I never heard of carbon trioxide, but you should take a closer look at carbon monoxide. What would happen if most of the carbon did not react to the dioxide but the monoxide?

Then the CuO would be excessive instead of the C? But do you really count "leftovers" as something that form in a chemical reaction?

 

[DrDu]

No, but this at least could explain your observation.
There is still another possibility, if really CuO where there in excess, namely that some Cu2O did form. What appearance do you expect for Cu2O?

 

[mertzi]

I don't understand the last question? Do you mean how it looks? I don't know how it looks, google image search says it looks red/orange. Actually I think other students had this happen, me and my lab partner were the only who got much solid copper, we saw this when we disposed our product. Our product didn't have anything red in it but others did.

 

[DrDu]

Ok, so probably at least some of your class mates got some copper-I-oxide and this was what your teacher was referring to.
You could try to cook up some reaction equations.

 

[mertzi]

OK! Could this be because how well distributed your mixture of CuO and charcoal is before applying heat?

 

[DrDu]

Yes. Another factor is the reaction of the coal with oxygen from air.

 

[mertzi]

Ok thank you for your help!

 

[DrDu]

You are welcome!