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I know that to perform a chemical test for $\ce{H2}$ we have to take a burning candle flame near to the mouth of the test tube and a blue flame with a characteristic pop sound confirms the presence of hydrogen. But my question is that, is there any other chemical test for hydrogen except this one with a pop sound?

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    $\begingroup$ No common chemicals tests exist for hydrogen. Certain metals absorb hydrogen but their prices are so high that it is impossible to include them in teaching schools. In fact this test is also non-specific. Methane would do the same. However physical tests like spectroscopy from a hydrogen discharge tube is extremely reliable. $\endgroup$
    – AChem
    Jun 18, 2023 at 17:41
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    $\begingroup$ As per the spectroscopy suggestion by @AChem, here is the visible region spectrum produced by electrical excitation of hydrogen gas in a gas discharge tube: physics.stackexchange.com/a/768678/313612. Nothing else looks like that, even deuterium gas. $\endgroup$
    – Ed V
    Jun 18, 2023 at 20:10
  • $\begingroup$ Anyway if there is a $CO_2$ dectector and the reaction do not produce $CO_2$, the gas is likely to be $H_2$. $\endgroup$
    – M06-2x
    Jun 18, 2023 at 20:13

4 Answers 4

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There are metals that promote the catalytic oxidation of hydrogen in air, such as platinum and palladium. While these are fairly expensive in bulk, there are reasonably inexpensive sensors which use micrograms of these catalytic metals to detect hydrogen, and other gases.

However, as you can see from the specifications for the MQ-8 sensor, it is not hydrogen-specific. That sensor also detects "alcohol" vapor, and even propane, though it is less sensitive to those gases than hydrogen.

BTW, the "POP" test is certainly not specific, either, and you'd get a bigger bang (and soot) from acetylene.

So, this test might not be exactly what you want:

  • It relies on electrochemistry.
  • It does not differentiate $\ce{H2}$ from $\ce{CH3OH}$, $\ce{C2H5OH}$, $\ce{C3H8}$, etc.

However, such a sensor is very useful where batteries are charged, or hydrogen gas is used, to warn of leaks.

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  • $\begingroup$ Possibly hydrogen is distinguished by the voltage at which it oxidizes, versus other gases the sensor detects. $\endgroup$ Jun 19, 2023 at 1:43
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    $\begingroup$ @OscarLanzi, actually, the sensor is based on electrothermal, rather than electrochemical measurements. It is not potentiometric electroanalytical chemistry. figaro.co.jp/en/technicalinfo/principle/catalytic-type.html $\endgroup$ Jun 19, 2023 at 18:27
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I would be inclined to create two half-cells, the one a standard hydrogen electrode, and the other, the gas under test, connected with a narrow tube as recommended with the Standard Hydrogen Electrode to avoid mixing.

The source for the hydrogen of the reference tube can be from purchased Hydrogen gas, or also from electrolysis with water formed hydrogen.

When the half-cells are connected with the narrow tube, with one half-cell having the gas under test and the other half cell having $\ce{H2}$, the potential difference can be measured with a digital volt-meter as the potential difference between the cathode and the anode under very small current flow conditions.

The picture link for one half of this setup is here

Author attribution:

standard electrode half-cell picture

The scheme of the standard hydrogen electrode:

  1. platinized platinum electrode
  2. hydrogen gas
  3. solution of the acid with activity of $\ce{H+} = \pu{1 mol dm−3}$
  4. hydroseal for preventing oxygen interference
  5. reservoir through which the second half-element of the galvanic cell should be attached. The connection can be direct, through a narrow tube to reduce mixing, or through a salt bridge, depending on the other electrode and solution. This creates an ionically conductive path to the working electrode of interest.

If the voltage difference is $0$ $\pu{Volts}$ then the gas is diatomic hydrogen. Just to mention that below this result is in combination with the flame test which eliminates inert gases as producing the zero voltage. Other reference gases (like Oxygen) can be also used in the reference cell verifying the Standard Electrode Potential tables values given there -- to eliminate gases that are producing zero voltage because of their lack of reactivity at one of the electrode sites.

It can (and should in my opinion) also be further tested with the flame test above. The test setup can be verified as previously stated using diatomic oxygen using the standard electrode potential for diatomic oxygen from the standard electrode potential table.

The details about calculating the potential difference between two standard potential cells is at this link here.

Together with the flame test above with its pop as kind of a generic test, the two-electrode cell test using two separate reference gases like $\ce{H2}$ and $\ce{O2}$ should provide the additional confidence that the gas is indeed hydrogen.

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Small amounts of hydrogen can be tested by methods using electrochemistry, as illustrated in two answers above.

Larger amounts, on the order of 50 - 100 mL, can be tested and identified by the unique property of hydrogen gas: its low density.

This is the procedure: weigh a small rubber balloon. Blow it up with air to about 50 - 100 mL and weigh again. The weight should be marginally higher to reflect the contents - and higher pressure - (on the order of 50 mmHg, or 6.5% of normal air pressure) inside the balloon. For highest accuracy, it's best to pump up the balloon with a tire pump rather than with your mouth, in order to eliminate the variability of humidity/saliva and CO2. The increase in weight for 100 mL of air will be about 0.129 gram, easily observable. This also gives you some practice and can be done repeatedly to ascertain error limits.

It may be more difficult to figure out an easy way to pump the suspicious gas into the balloon, but connecting the balloon to the gas volume and flooding that container with water can be arranged to drive the gas into the balloon. Corrections for the water (humidity) concentration can be made if necessary. Measure the volume of the inflated balloon; small balloons can be purchased that blow up almost spherically, and the calculations can be approximations. H2 at atmospheric pressure, neglecting the water vapor contribution, will weigh 0.00899 grams, giving a buoyancy of 0.120 grams, which is easily measured on a flat-top balance (see picture). Even a mechanical balance can be used (second picture). The open top allows balloons of various, even large, sizes.

enter image description here

enter image description here

The buoyancy for 100 mL helium will be 0.102 grams, and to be realistic, this will probably be within your error of measurement. However, helium won't burn; it will even snuff a (small) flame.

I've done this to distinguish between hydrogen and methane, and confirmed it by the soot spot left by methane on a cool watch glass.

The methane was also confirmed by gas IR. Gas IR can be used as a partial identification of hydrogen by virtue of no peaks in the usual IR region, compared to, say, a hydrocarbon gas. Helium would also not absorb, but would be eliminated by its nonflammability. A gas IR cell can be made with a section of copper tube (about 7 cm long, or as long as can be placed in the IR analyzer) with salt plates attached to either end. Suitable holes drilled into the copper tube with attached copper tubing can be provided with stopcocks and the cell can be filled with the aid of a water pump arrangement as discussed above.

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There is a recent article in J Chem Edu (https://doi.org/10.1021/acs.jchemed.3c00129 ) that describes an assay based on Pd-catalyzed reduction of organic dyes (methylene blue or thionine). The palladium is loaded on the surface of ZnO-particles to decrease cost and toxicity, allowing the experiment to be used in a middle-school setting. The assay is reusable as you can reoxidize the dyes with molecular oxygen.

The article mentions a commercially available kit (e.g. https://www.h2bluetest.com/) to test hydrogen concentration in water. Apparently, this caters to a new fad of ingesting elemental hydrogen as an antioxidant (doi: 10.18632/oncotarget.21130).

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