Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: trianluz on October 13, 2006, 08:59:50 PM
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After my previous experiment, I decided the react the impure mix of Cu2O and CuO with some NaOCl. This resulted in a black solid powder(I assume it to be CuO) and some gas was released during the reaction.
What might this gas have been?
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Well I do know that bleach can create chlorine gas when mixed with several substances, such as strong acids, hydrogen peroxide, or ammonia. This is what makes it, sometimes, a deadly substance for janitors who fail to read warning labels.
Hmm... well if I had to make a hypothesis on the site I guess I'd say that the Cu+ ion in Cu2O was oxidized by the H+ ion, which then reacted with the ClO- ion to create water and chlorine gas.... very rough, but I hope I gave you some ideas.
Was the gas collected coloured in any way?
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Can we assume that water was the solvent?
Cu2O
CuO
NaOCl
H2O
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The gas is oxygen. Hypochlorite is quite unstable and easily is decomposed in alkaline environments (as it is in bleach) to chloride and oxygen. Many metal oxides and metal hydroxides are a catalyst for decomposition of hypochlorite. Most notably cobalt hydroxide is, but almost all transition metal compounds are.
The black solid you obtain is copper (II) oxide.
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Woelen - What happens to the Chlorine
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So this would be the reaction:
Cu2O + 3NaOCl --> 2CuO + O2 + 3NaCl
Since this is redox, this would be the net ionic reaction:
Cu2O + OCl- --> Cl- + CuO + O2
In which Cu is oxidized and Cl is reduced.
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The reaction equation you give is technically correct, but I can give an infinity of other equally correct ones.
E.g. Cu2O + 5NaOCl --> 2CuO + 2O2 + 5NaCl
Cu2O + OCl(-) --> Cl(-) + 2CuO
Cu2O + 3OCl(-) --> 3Cl(-) + 2CuO + O2
Cu2O + 5OCl(-) --> 5Cl(-) + 2CuO + 2O2
Which one is correct? You cannot say that. In fact, there are two independent reactions occurring, and each of them has their own unambiguous reaction equation.
First, there is oxidation of Cu2O to CuO by the hypochlorite:
Cu2O + OCl(-) --> Cl(-) + 2CuO
Second, there is the catalytic decomposition of the hypochlorite:
2ClO(-) ---> 2Cl(-) + O2
All the reaction equations, given at the start of the post (and also given bij trianluz) can be written as linear combinations of the two basic reactions, I have given here. So, for chemical understanding it is much better to identify the two separate reactions, than trying to give a single reaction equation, which never will capture the real behavior, because of its ambiguity.
@billnotgatez: Now it should be clear what happens to the chlorine in the hypochlorite.
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Hypochlorite reacts with CO2 and water to give Cl2. Since traces of CO2 are everywhere, a minute amounts of chlorine cannot be excluded.
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@ woelen - thank you
@ AWK and all - thank you also
I still wonder if water does factor some way into the main reaction.
E.g. Cu2O + 5NaOCl --> 2CuO + 2O2 + 5NaCl
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Water indirectly plays a role in this reaction. It acts as solvent for the hypochlorite, otherwise you would have a solid/solid reaction, which is extremely slow, due to bad contact of reactants.
Also, in the catalytic decomposition reaction, water plays a role, but net consumption or production equals 0.