How can we detect hydrogen?
Step-by-step instructions of obtaining hydrogen
All reactions for determining a certain substance are called qualitative – i.e. they give a high probability that as a result of reactions, it will be possible to identify a certain substance (but sometimes this does not give result that is 100% precise, because when the reaction is conducted in a mixture of ions qualitative features may be masked). As far as hydrogen is concerned, such liquid phase reactions do not exist at present. So it is not yet possible to prove the presence of hydrogen by reacting different chemically active substances with one another. However, there are also other methods that allow us to do this.
Another question is how relevant this is, and whether there is any point in it. Hydrogen (the name of this substance in Latin means “generating water”, which reflects its essence) is an explosive gas and should not be worked with in a school laboratory, let alone at home.
You should not put yourself and your family in danger. However, if necessary, the presence or absence of hydrogen can be determined following the method described below (note that we will still not be able to obtain pure hydrogen – there will be some mixtures of gases in any case).
What does this method involve?
To start with we should mentioned another aspect that has fundamental significance – hydrogen exists in nature in the form of three isotopes. The most widespread is “protium”, the second “deuterium” and the third “tritium”.
In this article, we are only concerned with determining protium – i.e. the most widespread isotope of hydrogen, with a molecular mass of 1. Hydrogen shows a high reactive ability in the form of its chemical structure, so experiments must be carried out in accordance with all safety norms. Click here to see awesome experiments with hydrogen.
So, let us look at how we determine the presence of hydrogen in a mixture of gases, step by step.
- Take a test tube of high-melting glass, sprinkle fine iron filings into it (or even better, ground the iron to a powder, as the finer the reacting substance is, the greater the chances of a successful experiment – it is not easy to do).
- Then water is added to the ground iron – this should be done with a pipette, just a few drops, no more. After the water is absorbed, place another layer of iron on top – also finely ground.
- Then seal the test tube tightly by placing a rubber stopper in the neck of the test tube, with a hole in the center (into which a bent glass outlet tube will be inserted).
- The opposite end of this pipe must be placed in another container (test tube), which should be turned upside down. A water seal is also required – the hydrogen that passes through it will force water out of the test tube.
- The next step is to attach the two test tubes, and intensely heat the one with iron in it. A chemical reaction will take place, which can be described as follows:
2Fe + 3H₂O = Fe₂O₃ + 3H₂
Gas goes out through the pipe, and is easily determined by the appearance of bubbles in the water seal. However, another question arises – how can we confirm that it is really hydrogen, and not some other substance?
It’s all very simple. Take the test tube containing gas, holding it upside down, and bring a smoldering candle lighter to the open end. If the test tube contained pure hydrogen, without any other mixtures, there would be a loud noise resembling a whistle. However, this will not happen, as the gas mixture will contain air in any case. So when you conduct this experiment, you will hear a loud pop. This sound will confirm that you have obtained hydrogen, and that the experiment was conducted correctly.
Remember – test tubes must be undamaged and leakproof. Even the smallest crack may lead to an explosion.