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Why the hydrogen gas should be bubbled continuously through the electrolyte in a hydrogen electrode?

  1. To keep the solution saturated with hydrogen gas
  2. To clear the platinum electrode
  3. To gate the highest electrode potential
  4. To minimize loss of current
  5. To speed up the process
  6. To minimize the cost

In my opinion:

  1. This is false because the solution doesn't need to be saturated.
  2. Maybe true because if the platinum electrode is full with hydrogen gas which isn't bubbled continuously, there will not be enough space on platinum electrode to let another $\ce{H2}$ gas dissociate.
  3. This is false because it doesn't relate.
  4. Maybe true because if the hydrogen gas isn't bubbled continuously, $\ce{H2}$ will not dissociate continuously and will not transfer electrons. So there will be lack of current through this electric cell.
  5. Maybe true because if there's lack of current, it means that the process is too slow.
  6. False because this choice doesn't relate.

But the question asks to choose just one choice. What choice is the best? Do my reasons for each choice make sense?

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    $\begingroup$ Is this talking about the standard hydrogen electrode? If you want a steady response and not deplete the H2 gas you need to continuously bubble hydrogen. The correct answer is the first one, you want to saturate the solution to whatever pressure you have of hydrogen gas, otherwise the concentration in solution will change over time and so will your potential. $\endgroup$
    – Noah
    Commented Aug 11, 2023 at 7:58
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    $\begingroup$ It is the Pressure of H2 at the electrode not the dissolved H2 in solution. The answer is probably to maintain the correct [max?] potential. The question is confusing to one who actually thinks about it because current is related to potential even tho the cell is measured at zero current draw. The questioner, as most of us, has probably never used or seen a hydrogen electrode. $\endgroup$
    – jimchmst
    Commented Aug 12, 2023 at 0:08

2 Answers 2

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The hydrogen gas is the reactant of the half reaction, so it has to be present:

$$\ce{H2(g) ->[Pt(s)] 2H+(aq) + 2e-}$$

The platinum electrode is the catalyst, and water is the solvent or proton acceptor for the hydrogen ions that are generated. Once the hydrogen adsorbed on the platinum surface is depleted, the half reaction stops unless you supply more hydrogen gas.

In a standard hydrogen electrode, the pressure of the hydrogen gas is important because the voltage measured will depend on the pressure.

I am glad I don’t have to answer the multiple choice question posted by the OP. None of the answers seem appropriate.

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Hydrogen gas must be bubbled into the solution so that it is able to oxidize by losing electrons which they can't just in air. Platinum electrode need not be cleaned. Potential depends upon concentration of hydrogen, by "Nernst" equation. If hydrogen was there or not, current can never be lost, speed of process is kinetics and in no way related to thermodynamics. Cost, rubbish.

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    $\begingroup$ oxidize H2 or reduce H+. Last[penultimate?] sentence is confusing. Pt black takes care of the reaction rates. To measure the thermodynamics accurately [voltages] the kinetics must be sufficient, so they are relevant. $\endgroup$
    – jimchmst
    Commented Aug 13, 2023 at 20:55

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