Pasco PS-2108 Dissolved Oxygen Sensor Manuel d'utilisateur télécharger pdf (Page 14)

PASPort Dissolved Oxygen Sensor Model No. PS-2108

Theory of Dissolved Oxygen:

What is the chemical mechanism by which diatomic oxygen dissolves in water?

This is a particularly eloquent description of the mechanism of oxygen solubility in water:

[from Water on the Web

]

Water, as a polar molecule, induces an accumulation of electron density (dipole moment) at one end of nonpolar

gas molecules such as oxygen (O

) and carbon dioxide (CO

). In animation, observe a polar water molecule

approaching a nonpolar O

molecule. The electron cloud of O

is normally distributed symmetrically between

the bonded O

atoms. As the negative end of the H

O molecule approaches the oxygen molecule, the electron

cloud of the O

moves away to reduce the negative-to-negative repulsion. As a result, a dipole (a molecule with

positive and negative charges separated by a distance) has been induced in the nonpolar O

molecule, causing O

and H

O to become weakly attracted to each other. This intermolecular attraction between the oppositely charged

poles of nearby molecules is termed a dipole- induced dipole force. The creation of these forces then explains the

mechanism by which gases dissolve in water.

Still images from the Water on the Web animation:

II. What factors influence the amount of dissolved oxygen in water? There are several

factors that can influence the amount of gaseous diatomic oxygen (as well as other gases) that

will dissolve in water. When speaking of gases dissolving in water, discussion is limited to

gases that do not chemically react with the water.

Induced Dipoles

The electron cloud of an isolated Oxygen

molecule is distributed symmetrically

between the bonded O atoms.

As the negative end of the polar water

molecule approaches…

…the O

electron cloud is moved away to

reduce repulsion between the O

cloud and

the negative end of the water molecule.

The O

molecule itself becomes polar.

A dipole has been induced in the otherwise

nonpolar O

molecule. The H

O and the O

are now weakly attracted to one another.

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Pasco PS-2108 Dissolved Oxygen Sensor Manuel d'utilisateur Page 14

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