When the ethanol, C2H5OH, vapour is passed through the tube it is oxidised to carbon dioxid, and water. Correspondingly, the dichromate ions which are yellow in colour, are reduced to chromate ions which are green in colour. This results in the observed colour change from yellow to green when alcohol is present in the exhaled breath.
HA <==> H(+) + A(-)
Acid Base
Here the acid, HA, and the base, A(-), which differ from one another by a proton, are described as a conjugate pair, (i.e. the Base, A(-), is said to be conjugate base of the Acid, HA).
It should be noted that the hydrogen ion exist in aqueous solution as a hydrated proton, H3O(+).
HCl + H2O ==> H2O(+) + Cl(-)
Acid2 Base2 Acid1 Base1
Bronsted and Lowry proposed that
An Acid is a Proton Donor
A Base is a Proton Acceptor
Thus, the ionisation of sulphuric acid satisfies this concept of an acid, in that it donates a hydrogen ion to water.
H2SO4 + H2O ==> H3O(+) + HSO4(-)
Proton Hydrated
Donor Proton
Similarly, the hydroxyl ion is a base, as it can accept a proton from the hydrated proton.
H3O(+) + HO(-) ==> 2 H2O
Proton
Acceptor
It should be noted that the hydrogen ion exist in aqueous solution as a hydrated proton.
In 1828, Robert Brown observed the motion of pollen grains which were suspended in water. When these pollen grains were viewed through a microscope, the grains were seen to move in an erratic manner. They traveled along short straight paths, but the individual grains were rarely seen to collide with each other. The path of any one grain can best be described as a zigzag line, with a straight path between each zig and zag. This zig-zag motion is called Brownian Movement.
The irregular paths strongly suggest that the visible grains are pushed by invisible particles that are moving at random and which collided with the grains of pollen. If the water molecules are in motion, moving about at random, this would allow an explanation for the observations. This observation of Brownian Motion is one of the supporting pieces of evidence for the Atomic Theory and for the Kinetic theory of gases.