How can we detect 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.

The method is based on the prop­er­ty of met­als re­act­ing with wa­ter to form an ox­ide and to re­lease hy­dro­gen as a side prod­uct of the chem­i­cal re­ac­tion.

So, let us look at how we de­ter­mine the pres­ence of hy­dro­gen in a mix­ture of gas­es, step by step.

1. 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).
2. 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.
3. 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).
4. 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.
5. 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.