Properties and Uses of Hydrogen

Physical Properties

1. It is a colorless and odorless gas.
2. It is neutral to litmus.
3. It is the lightest gas (much less dense than air).
4. It burns in air but will not support the combustion of other things - it extinguishes a lighted splint pushed up into it.

2H_2(g) + O_2(g) → 2H₂O_(l)

Chemical Properties

1. Reducing action - hydrogen, being a strong reducing agent reduces the oxides of copper, lead, iron and zinc to their respective metals, while the hydrogen is oxidized to form water when the metal oxides are heated in a stream of hydrogen.

CuO_(s) + H_2(g) → Cu_(s) + H₂O_(g)

Fe₂O_3(s) + 3H_2(g) → 2Fe_(g) + 3H₂O_(g)

PbO_(s) + H_2(g) → Pb_(s) + H₂O_(g)

2. Combination reactions - hydrogen combines directly with certain metals by gaining electron(s) to form electrovalent compounds called hydrides:

2Na_(s) + H₂ → 2NaH_(s)

Ca_(s) + H_2(g) → CaH_2(s)

Note: lithium tetrahydridoaluminate(lll), also called Lithium aluminium hydride, LiAlH₄ and sodium hydridoborate(lll) are very powerful reducing agents commonly used in organic chemistry.

3. Hydrogen also combines directly by electron sharing (covalency) with certain non-metals. E.g. with oxygen. Hydrogen combines with oxygen with the application of a flame (giving a pale blue flame) to form steam.

2H_2(g) + O_2(g) → 2H₂O_(g)

4. With halogens - hydrogen combines directly with the halogens (Cl, Br, and I) to form compounds known as halides. E.g.

Cl_2(g) + H_2(g) → 2HCI;

Br_2(g) + H_2(g) → 2HBr_(g);

I_2(g) + H_2(g) → 2HI_(g)

Note: * These reactions are catalyzed in the presence of sunlight (very vigorous in bright sunlight and slower in diffused light)

* The degree or vigor of the reaction decreases downward in the group, i.e. Cl >Br > I.

Test for Hydrogen: a mixture of small quantity of hydrogen and air produces a pop sound (with the burning of the hydrogen) when a lighted splinter is introduced.

Note: a mixture of large quantity of hydrogen and air explodes when a flame is applied.

Uses of Hydrogen

1. For energy or power generation - this is the current most popular use of hydrogen - from powering cell phones, rockets and automobiles, to distributed electrical generation applications. As fuel for Industrial and domestic heating - hydrogen is preferred as fuel rather than coal or any other fossil fuel because it burns without producing environmentally polluting gases - hydrogen is the cleanest of all fuels.

2. For filling balloons - due to its lightness. However, because it is very flammable, it is rarely used.

3. In the hardening of oils to make margarine.

4. In the manufacture of ammonia - this is the second most important use of hydrogen.

5 In the manufacture of HCI and organic chemicals, such as methanol.

6. In oxy - hydrogen flame for cutting and welding steel - this is as a result of the enormous heat produced when hydrogen is burnt in oxygen.

Hydrogen
Production of Hydrogen