Zinc and Hydrochloric Acid

flumbie

I'm having some trouble understanding what happens when Zinc and Hydrochloric acid are reacted with Copper Sulfate as a catalyst. I *think* the Copper ion gets electrons from the zinc and turns into straight copper which leaves zinc free to react with the chlorine to form zinc chloride. Does this affect the rate at which hydrogen are formed because the electrons are going from the zinc to the copper instead of from the zinc to hydrogen? Any help much appreciated.

flumbie

bumped
Does no one know or do you just not want to tell me?

Kushal

i guess this is what happens....

the Cu++ is reduced by zinc to Cu and the zinc is oxidised to Zn++. the Zn++ reacts with the Cl-.

the Cu is then oxidised back to Cu++ by H+ which gets reduced to H2

overall reaction: Zn + 2HCl -----> ZnCl2 + H2

lightarrow

This do really happens, and quite fast, even without HCl, in water, so it's certainly one of the possible reactions.Zn++ don't react with Cl- in water solution, and Cu cannot be oxidated from H+ in the absence of strong complexants of Cu++. Don't know what really happens but that explanation is not correct.
Certainly.

To flumbie: are you sure it was Zn, HCl and CuSO4?

Kushal

Zn, HCl and CuSO4 works, i remember my teacher saying it.

and of course ZN++ does not REACT with Cl-, the ions remain in solution because ZnCl2 is a strong electrolyte.

but there has to be a way for Cu to get back to Cu++ and H+ to get to H2.

chemisttree heeelp!!!

lightarrow

It does certainly work, but is there really the need of Cu++ as catalyst? If I remember correctly, Zn should react quite fast even with HCl only.

flumbie

It's actually a pretty slow reaction (using 3M HCl at least).

flumbie

Its not the Cu++ thats the catalyst its actually Cu. The copper ions in the CuSO4 are reduced by zinc which provides a coating of copper to cover the zinc. An electrolytic cell is made where the more reactive metal (Zn) is the anode and Cu is the cathode, with the HCl acting as an electrolyte. This means the hydrogen ions are more likely to be reduced at the cathode which results in a faster reaction rate. The Cu doesnt change back to Cu++ at the end of the experiment which does meant that slightly less hydrogen will be produced however this shouldn't affect the rate of the experiment overly much.

Thanks for the help anyway

lightarrow

And thanks to you to have explained this, it's something interesting I was not aware of. I'm sorry we couldn't help you and I hope you will keep asking interesting questions and that we could help you, next time!
Regards.

Kushal

yeah.... thank you for posting the actual mechanism :)