Zn + dil. H 2 SO 4 → H 2 (g) + ZnSO 4This equation shows the usual laboratory method of preparing hydrogen.
Mossy zinc is used in a setup as shown in Figure 18. The acid is introduced down
the thistle tube after the zinc is placed in the reacting bottle. In this sort of setup,
you would not begin collecting the gas that bubbles out of the delivery tube for a
few minutes so that the air in the system has a chance to be expelled and you can
collect a rather pure volume of the gas generated.
Figure 18. Preparation of an Insoluble Gas by the Addition of Liquid to Other
ReactantIn industry, hydrogen is produced by (1) the electrolysis of water, (2)
passing steam over red-hot iron or through hot coke, or (3) by decomposing
natural gas (mostly methane, CH 4 ) with heat (CH 4 + H 2 O → CO + 3H 2 ).
PROPERTIES OF HYDROGEN. Hydrogen has the following important physical
properties:
- It is ordinarily a gas; colorless, odorless, tasteless when pure.
- It weighs 0.9 gram per liter at 0°C and 1 atmosphere pressure. This is
as dense as air. - It is slightly soluble in water.
- It becomes a liquid at a temperature of −240°C and a pressure of 13
atmospheres. - It diffuses (moves from place to place in gases) more rapidly than any
other gas. This property can be demonstrated as shown in Figure 19.