Chemistry experiment question - H2O2 liberating hydrogen?!

[TheRoundaboutHadLovelyFlowers]

Hi,

I wondered if I could ask a question about a chemistry experiment that we are doing with our chemistry set here?

We did this reaction to try to make oxygen, that would then relight a glowing splint. It did make the splint glow, but we heard a very clear popping sound, which possibly means that our reaction had also produced hydrogen.

I just wondered if anybody might know why it would do that? We can't figure it out.

Here is what we did:

In a test tube we mixed:

CuSO4.H2O + Na2CO3 + 3% H2O2.

The mixture rapidly produced bubbles of clear gas, which we trapped in a test tube. When we put a glowing splint in, the splint glowed very brightly, but did not reignite.

As a last step, we took the stopper off the top of the tube that contained the reaction mixture and put a glowing splint in there. We saw the splint grow brightly. We also heard a very pronounced popping sound, just like sound we heard when we put a lit match into hydrogen yesterday.

As we understand it, the reaction happens because H2O2 is a reducing agent, and by acting to reduce the other chemicals, it breaks down into H2O and O2. But we are not sure why we would be getting H2 (Hydrogen gas).

We wondered if anybody might know why the hydrogen was there?

Thanks!

Did you have anything in the reactants test tube previously or clean it with anything specific?

Are you sure it was a 'pop' rather than a crackle with the hot splint coming into contact with a wet surface?

Hi,

Thanks for asking. No the tube was completely clean and the sound was a clear pop, with no contact between the match and the water.

It's odd because there really shouldn't be hydrogen there. Not sure what else it could have been.

Thanks!