Chemistry - Hydrogen (Preparation, Properties, Uses)

Hydrogen is the first element in the periodic table, represented by the symbol $H$ and atomic number $1$. It exists as a diatomic molecule $H_2$.

In the laboratory, hydrogen is prepared by the action of dilute $HCl$ or dilute $H_2SO_4$ on granulated zinc ($Zn$). Granulated zinc is preferred because it contains impurities like copper which act as a catalyst, speeding up the reaction.

Hydrogen gas is collected by the downward displacement of water because it is nearly insoluble in water and is lighter than air.

Industrial preparation via the Bosch Process involves two steps: first, producing water gas ($CO + H_2$) by passing steam over red-hot coke at $1000^{\circ}C$, and second, reacting water gas with excess steam in the presence of $Fe_2O_3$ and $Cr_2O_3$ catalysts.

Hydrogen is a powerful reducing agent. It removes oxygen from metallic oxides like $CuO$ or $PbO$ when passed over them at high temperatures.

Hydrogenation is the process of adding hydrogen to vegetable oils (unsaturated fats) in the presence of a nickel ($Ni$) catalyst at approximately $200^{\circ}C$ to form solid vanaspati ghee (saturated fats).

Hydrogen is highly combustible and burns in air with a pale blue flame to form water ($H_2O$), but it is not a supporter of combustion.

The 'Pop' test: A burning wooden splinter brought near a test tube of hydrogen gas will extinguish with a characteristic 'pop' sound, which is a confirmatory test for hydrogen.