Editing Hydrogen (section)

===Laboratory syntheses===
{{chem2|H2}} is produced in laboratory settings, such as in the small-scale [[electrolysis of water]] using metal [[electrodes]] and water containing an [[electrolyte]], which liberates hydrogen gas at the [[cathode]]:<ref name="housecroft" />
:{{chem2|2H+(aq) + 2e− → H2(g)}}
Hydrogen is also often a by-product of other reactions. Many metals react with water to produce {{chem2|H2}}, but the rate of hydrogen evolution depends on the metal, the pH, and the presence of alloying agents. Most often, hydrogen evolution is induced by acids. The alkali and alkaline earth metals, aluminium, zinc, manganese, and iron react readily with aqueous acids.<ref name="housecroft">{{ cite book | title = Inorganic Chemistry | last1 = Housecroft | first1 = C. E. | last2 = Sharpe | first2 = A. G. | year = 2018 | publisher = Prentice Hall | edition = 5th | isbn = 978-1292134147 |pages = 219, 318–319}}</ref>
:{{chem2|Zn + 2 H+ → Zn(2+) + H2}}

Many metals, such as [[aluminium]], are slow to react with water because they form passivated oxide coatings of oxides. An alloy of aluminium and [[gallium]], however, does react with water. At high pH, aluminium can produce {{chem2|H2}}:<ref name="housecroft" />

:{{chem2|2 Al + 6 H2O + 2 OH- → 2 [Al(OH)4]- + 3 H2}}