Question

we have done experiment in school and for homework we must write chemical reactions that have happend during the experiment.
the experiment was like this : first we took an unknown substance than we have put some CuO , we mixed that two substances together in test tube. Than we put cotton in that test tube a than we put CuSO4.Than we heat test tube . On the aperture of tube we put glass with water in , and we still heat tube. and that was that. And I really don't know how to write reactions. Teacher said something about writing CxHy instead of unknown substance. Can someone helpp me because i don't understand this , and i must get a good grade . Thanks