How to determine hydrogen (H2​) using a Orsat gas analysis apparatus?

To determine hydrogen (H2​) using an Infralab Orsat gas analysis apparatus, you typically need a four-test type or a modified apparatus equipped with a slow combustion pipette. Here’s the general procedure:

Prerequisites:

• The Orsat apparatus must have absorption pipettes for CO2​, O2​, and CO.
• It needs to be equipped with a slow combustion pipette containing a palladium asbestos catalyst and a means to introduce oxygen.

Procedure:

1. Perform standard Orsat analysis: First, analyze the gas sample for carbon dioxide (CO2​), oxygen (O2​), and carbon monoxide (CO) using the standard absorption pipettes in the usual manner. Note the volume remaining after each absorption.
2. Introduce the remaining gas to the combustion pipette: After absorbing CO2​, O2​, and CO, the remaining gas in the burette (which would primarily consist of H2​, N2​, and other inert gases) is carefully transferred to the slow combustion pipette.
3. Add a known volume of oxygen: A measured volume of pure oxygen (in excess of what’s needed for combustion) is introduced into the combustion pipette along with the remaining gas sample.
4. Catalytic Combustion: The palladium asbestos catalyst in the pipette facilitates the combustion of hydrogen with the added oxygen according to the reaction: 2H2​+O2​→2H2​O The reaction proceeds slowly over the catalyst. Sufficient time must be allowed for complete combustion. The water formed is in the vapor phase at the temperature of the apparatus, but its volume is negligible compared to the gaseous reactants and products under these conditions.
5. Measure the contraction in volume: After the combustion is complete and the apparatus has returned to the initial temperature and pressure, the new volume of the gas in the combustion pipette is measured by returning it to the burette and leveling the liquid. The contraction in volume observed is related to the volume of hydrogen that was present.

Calculation:

Let:

• V1​ = Volume of the gas remaining after the absorption of CO2​, O2​, and CO.
• VO2​ added​ = Volume of oxygen added to the combustion pipette.
• V2​ = Volume of gas remaining after combustion and returning to the initial temperature and pressure.

The change in volume due to the combustion of hydrogen is (V1​+VO2​ added​)−V2​.

From the stoichiometry of the reaction (2H2​+O2​→2H2​O), 2 volumes of hydrogen react with 1 volume of oxygen to produce a negligible volume of water vapor (in the context of gas volume measurement at the Orsat’s operating conditions). Therefore, the contraction in volume is equal to the volume of hydrogen that reacted plus the volume of oxygen consumed.

Let VH2​​ be the volume of hydrogen. The oxygen consumed is VH2​​/2.

So, the contraction in volume =VH2​​+(VH2​​/2)=1.5×VH2​​.

Therefore, the volume of hydrogen (VH2​​) in the original sample (after CO2​, O2​, and CO removal) can be calculated as:

VH2​​=32​×(Contraction in volume)

The percentage of hydrogen in the original gas sample would then be calculated based on the initial volume of the gas sample taken for analysis (usually 100 ml).

In summary, determining hydrogen with an Orsat apparatus requires a special combustion pipette and involves catalytically burning the hydrogen with a known amount of oxygen and measuring the resulting contraction in volume.

If your Infralab Orsat apparatus is a standard three-test type (for CO2​, O2​, CO), it won’t have the capability to directly measure hydrogen. You would need a four-test type specifically equipped with a combustion pipette. You should consult the manual or specifications of your particular Infralab apparatus to confirm if it has this feature and for any specific instructions provided by the manufacturer.