Chemical reactions with the release of hydrogen

Hy­dro­gen is an abun­dant el­e­ment in na­ture and in the uni­verse, which holds first place in the Pe­ri­od­ic Ta­ble.

For ex­am­ple, hy­dro­gen is present in wa­ter, prac­ti­cal­ly all or­gan­ic sub­stances, stars and in­ter­stel­lar gas, ga­lac­tic plan­ets etc., so it is dif­fi­cult to over­es­ti­mate the im­por­tance of this el­e­ment in the world and the uni­verse. It is rarely en­coun­tered in free form; the vol­ume con­tent of hy­dro­gen in the air is around 5∙10-5. Hy­dro­gen H₂ is a light gas which has no smell, col­or or taste.

Ob­tain­ing pure hy­dro­gen in the lab­o­ra­to­ry is con­sid­ered to be one of the most dan­ger­ous ex­per­i­ments, be­cause H₂ is an ex­plo­sive and com­bustible gas in com­bi­na­tion with air.

Hy­dro­gen it­self is harm­less for hu­man life and is non-tox­ic. It should also be not­ed that this gas dis­solves in ethanol and sev­er­al met­als such as iron, nick­el, ti­ta­ni­um etc.

The his­to­ry of ob­tain­ing hy­dro­gen

As for the his­to­ry of ob­tain­ing hy­dro­gen, this gas has been ex­tract­ed ever since chem­istry be­came a sep­a­rate sci­ence, and the re­lease of a com­bustible gas was ob­served in the in­ter­ac­tion of met­als and acids.

Pre­vi­ous­ly in alche­my, the com­bustible gas re­leased was known as phlo­gis­ton, a hy­po­thet­i­cal su­perfine sub­stance made of fire, which filled all com­bustible sub­stances and was re­leased from them at the mo­ment of com­bus­tion. But the renowned Rus­sian poly­math Mikhail Lomonosov showed that in these re­ac­tions phlo­gis­ton was not re­leased. In 1766, this gas was called in­flammable air by the sci­en­tist Hen­ry Cavendish. At the mo­ment of com­bus­tion, this gas ac­tive­ly re­leased wa­ter, but Cavendish’s be­lief in al­chemic lore con­cern­ing the fiery sub­stance hin­dered him from draw­ing ob­jec­tive con­clu­sions. Lat­er in 1766, it was es­tab­lished that in­flammable air was present in wa­ter, and could be ex­tract­ed from it. These con­clu­sions were made by An­toine Lavoisi­er and Jean Meusnier.

Ar­eas of ap­pli­ca­tion

Hy­dro­gen is ac­tive­ly used in the chem­i­cal in­dus­try for the man­u­fac­ture of many sub­stances, for ex­am­ple am­mo­ni­um, methanol, and H₂ is also used for mak­ing soap and plas­tics.

In the food in­dus­try, mar­garine is made with hy­dro­gen. Hy­dro­gen is also used in air­craft con­struc­tion for in­flat­ing air­ships, but be­cause of its ex­plo­sive­ness it was re­placed with he­li­um.

At present stud­ies are be­ing con­duct­ed on re­plac­ing the tra­di­tion­al fuel of petrol with hy­dro­gen fuel.

Re­ac­tions with the re­lease of hy­dro­gen

At present, the most wide­spread method of ob­tain­ing hy­dro­gen on an in­dus­tri­al scale is the con­ver­sion of meth­ane CH₄ or nat­u­ral gas. Meth­ane is a nat­u­ral gas, a sim­ple hy­dro­car­bon. When meth­ane is heat­ed with wa­ter va­pors at high tem­per­a­tures (1000 °С), hy­dro­gen is re­leased:

CH₄ + Н₂О→ C + 2H₂

In in­dus­try, hy­dro­gen is also ob­tained by pass­ing wa­ter over red-hot coke.

Ob­tain­ing hy­dro­gen with Kipp’s ap­pa­ra­tus.

Kipp’s ap­pa­ra­tus is the best-known de­vice for ob­tain­ing gas­es, and con­sists of a flask, fun­nel and gas pipe. With this ap­pa­ra­tus, hy­dro­gen is ob­tained with zinc and hy­drochlo­ric and sul­fu­ric acid. The ap­pa­ra­tus makes it pos­si­ble to col­lect gas in a test tube or oth­er con­tain­er, but ex­per­i­ments with the re­lease of H₂ can also be car­ried out with­out it, sim­ply by adding a piece of zinc and hy­drochlo­ric acid to a test tube:

Zn + 2HCl → Zn­Cl₂ + H₂↑.

The re­ac­tion with the re­lease of hy­dro­gen from alu­minum and al­ka­li makes it pos­si­ble to ob­tain pur­er hy­dro­gen. This ex­per­i­ment can be car­ried out in the open air, by fill­ing an or­di­nary bal­loon with hy­dro­gen. It must not be car­ried out at home, as the ex­per­i­ment is po­ten­tial­ly high­ly ex­plo­sive.

2Al + 2NaOH + 6H₂O → 2Na[Al(OH)₄] + 3H₂↑

Here you’ll find safe ex­per­i­ments to do at home.

In­stead of alu­minum, you can use alu­minum foil: add it to a so­lu­tion of sodi­um hy­drox­ide.

Sodi­um hy­drox­ide is an or­di­nary flu­id used for clean­ing pipes which can be pur­chased at a hard­ware store. If you fill a bal­loon with hy­dro­gen, by plac­ing it over a flask from which the gas is re­leased, the bal­loon will rise into the air. Ob­tain­ing hy­dro­gen by this method is quite easy to ex­plain: the sur­face of the alu­minum is cov­ered by a spe­cial ox­ide film, which starts to break down on in­ter­ac­tion with al­ka­lis.

Re­ac­tion with the re­lease of hy­dro­gen us­ing cop­per sul­fate, alu­minum and salt

Add kitchen salt (sodi­um chlo­ride) and cop­per sul­fate Cu­SO₄∙5Н₂О to a flask. Then add wa­ter. The re­sult­ing mix­ture should turn green, but if the liq­uid re­mains trans­par­ent, add more salt and cop­per sul­fate. Then add pieces of alu­minum or foil rolled into a ball to the flask. The re­ac­tion of the re­lease of hy­dro­gen will be­gin, as the cop­per chlo­ride that forms in the flask will re­move the ox­ide film from the alu­minum.

Re­ac­tion with the re­lease of hy­dro­gen us­ing al­ka­line and al­ka­line earth met­als and wa­ter.

Lithi­um is a light al­ka­line met­al which does not sink in wa­ter. If you add a piece of lithi­um to luke­warm wa­ter, an im­me­di­ate re­ac­tion with the re­lease of gas will take place:

Li + H2O = LiOH + H₂↑.

Thus, when al­ka­line met­als come into con­tact with wa­ter, al­ka­li forms and hy­dro­gen is re­leased.

Re­ac­tion of the re­lease of hy­dro­gen us­ing cal­ci­um and wa­ter

Cal­ci­um is a soft al­ka­line earth met­al, and if you add pu­ri­fied metal­lic cal­ci­um to wa­ter, a vi­o­lent re­ac­tion takes place with the re­lease of hy­dro­gen and cal­ci­um hy­drox­ide:

Ca + 2H₂O → Ca(OH)₂↓ + H₂↑

Thus, when al­ka­line earth met­als come into con­tact with wa­ter, a base forms and hy­dro­gen is re­leased.

Ob­tain­ing hy­dro­gen by elec­trol­y­sis

The sim­plest method to ob­tain hy­dro­gen by elec­trol­y­sis is the hy­drol­y­sis of wa­ter. This method can be used to ob­tain pure oxy­gen and hy­dro­gen in the lab­o­ra­to­ry.

2Н₂О = 2Н₂↑ + О₂↑