Electrolysis of Water -- Rate of Reaction?

[Cheesycheese213]

I'm so sorry if this is a bad question!

I am doing an experiment measuring the rate of gas production (hydrogen) of the electrolysis of water, and I got myself a bit confused about whether I have been taking the correct measurements?

I had originally thought that, since the "concentration" of the reactant wouldn't change (and I was using a large container of water), the rate of reaction wouldn't change over time when keeping all other variables constant. Also, I didn't think the electrolyte concentration would be affected over time either (other than maybe a slight increase because of the decrease in water?).
So, when doing the experiment I didn't take measurements of the gas volume over intervals of time (ex. every 30 sec or something), and just kept the battery connected for a set amount of time and took one volume reading at the end.

I am worried that I misunderstood something, and was wondering if the rate of reaction/gas production in the electrolysis of water does actually change over time?

Thanks! :D

 

[jrmichler]

You just made a good case for doing the experiment again. Do you know the relationship between current and amount of gas produced? You should, then you would know why the current needs to be monitored.

Don't feel bad. It's normal to do an experiment, then realize that it needs to be done again because you learned something from doing it the first time.

 

[Henryk]

You also have to think about the pressure of the collected hydrogen. All gasses are easily compressible.

 

[Cheesycheese213]

You just made a good case for doing the experiment again. Do you know the relationship between current and amount of gas produced? You should, then you would know why the current needs to be monitored.

Don't feel bad. It's normal to do an experiment, then realize that it needs to be done again because you learned something from doing it the first time.

Hello! Thank you so much! I thought that an increased current with nothing else changing would mean the amount of gas produced also increases? I just did another trial checking the current and the volume every 30 seconds, the current stayed constant (0.15A) and the volume also increased by a constant amount.

I'm not too sure if I'm understanding correctly, but does it mean that as long as the current stays constant throughout the rate of gas production should also be constant?
Thank you again! :D

 

[Cheesycheese213]

You also have to think about the pressure of the collected hydrogen. All gasses are easily compressible.

Oh thank you, I forgot to consider that! :D

 

[Borek]

I suggest you read about Faraday's laws of electrolysis. While they don't address the reaction rate per se, they almost directly explain what to expect in your experiment.

 

[epenguin]

I don't know if this is what Borek meant, but for the rate, considering the chemical equation for the reaction, calculate the moles/s of electrons transported in the 0.15 A current ( look up 'Faraday constant'), and calculate, assuming standard pressure and temperature, from the volume the number of moles of H₂ produced, and see what the correspondence between these two experimentally independent measurements looks like.

 

[Cheesycheese213]

I suggest you read about Faraday's laws of electrolysis. While they don't address the reaction rate per se, they almost directly explain what to expect in your experiment.

I don't know if this is what Borek meant, but for the rate, considering the chemical equation for the reaction, calculate the moles/s of electrons transported in the 0.15 A current ( look up 'Faraday constant'), and calculate, assuming standard pressure and temperature, from the volume the number of moles of H₂ produced, and see what the correspondence between these two experimentally independent measurements looks like.

Thank you! I've done some of those calculations now, it helped a lot! I guess I hadn't really understood electrolysis very well when starting the experiment :,D. I really appreciate all the help!

 

[epenguin]

Thank you! I've done some of those calculations now, it helped a lot! I guess I hadn't really understood electrolysis very well when starting the experiment :,D. I really appreciate all the help!

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