14/01/11

Degree of Ionization


The degree of ionization refers to the proportion of neutral particles, such as those in a gas or aqueous solution, that are ionized into charged particles. A low degree of ionization is sometimes called partially ionized, and a very high degree of ionization as fully ionized.

Ionization refers to the process whereby an atom or molecule loses an electron, resulting in two oppositely charged particles, (1) a negatively charged electron and (2) a positively charged ion.

Chemistry usage

The degree of ionization, or α, is a way of representing the strength of an acid, often represented by the Greek letter alpha. It is defined as the ratio between the number of ionized molecules and the number of molecules dissolved in water. It can be represented as a decimal number or as a percentage. One can classify strong acids as having ionization degrees above 50%, weak acids with α below 5%, and the remaining as moderate acids, at a specified molar concentration.

Physics usage

In gases and plasma, the degree of ionization refers to the proportion of neutral particles that are ionized into charged particles. For example, when electricity passes through a novelty plasma ball, perhaps 1% of the gases are ionized (sometimes referred to as partially ionized). Our Sun and all stars contain largely hydrogen and helium gases, that are fully ionized into electrons, protons (H+) and helium ions (He++).
A gas may begin to behave like plasma when the degree of ionization is as little as 0.01%

History

Ionized matter was first identified in a discharge tube (or Crookes tube), and so described by Sir William Crookes in 1879 (he called it "radiant matter").[3] The nature of the Crookes tube "cathode ray" matter was subsequently identified by English physicist Sir J.J. Thomson in 1897,[4] and dubbed "plasma" by Irving Langmuir in 1928,[5] perhaps because it reminded him of a blood plasma.

Relation with electricity 

There are two kinds of compound based on ability for conducting electricity; electrolyte and non-electrolyte. Electrolyte conducts the electricity while non-electrolyte doesn't.
Electrolyte conducts the electricity because it is be able to ionize to form free mobile ions in the solution or molten form. 
Non-electrolyte is not be able to ionize. So, it doesn't conduct electricity.


Strength of ionization is gives measure of the degree of ionization ( α ) of an electrolyte.

Degree of Ionization is a value to show amount of molecules that ionized (mol) devided by amount of molecules (mol) in the face .


Based on this degree, the electrolytes can be classified as strong or weak electrolyte and non-electrolyte.


Strong Electrolyte
A strong electrolyte dissociates or ionizes completely or almost completely to form free mobile ions in the solution or molten form. The more the availability of free mobile ions in an electrolyte, the greater is its capacity to carry or conduct current i.e. the stronger the electrolyte. The ability to conduct current can be observed by setting up a cell as shown in figure 4.4. The bulb glows brightly.
Degree of ionization for strong electrolyte is 1.
 α = 1


Weak Electrolyte 
A weak electrolyte ionizes or dissociates only partially to form free mobile ions. Most of the electrolyte remains as un-ionized molecules. For example in acetic acid, the number of its dissociated ions (the acetate and hydrogen ions) is less compared to the total amount of acetic acid molecules present. Similarly in ammonium hydroxide the number of its dissociated ions (the ammonium and hydroxyl ions) are less compared to the total amount of the molecules present.

Thus both these compounds are weak electrolytes.

When the number of mobile ions is less in an electrolyte, the lesser is its capacity to carry or conduct current i.e. the weaker is the electrolyte. This is observed by setting up the cell as shown in figure 4.5. The bulb glows less brightly.
Degree of ionization for strong electrolyte is < 1.
 α < 1


Non-electrolyte 
A non-electrolyte does not provide ions in a solution and therefore current does not flow through such solution. The bulb in the given set up does not glow (Fig.4.6). Some examples of non-electrolytes are: alcohol, carbon tetrachloride, carbon disulphide.
Degree of ionization for strong electrolyte is 0.
 α = 0



Examples of Strong Electrolyte
Sea water , Hydrochloric acid, Sulphuric acid ,Aqueous copper sulphate ,Molten lead bromide ,Aqueous sodium chloride ,Nitric acid ,Aqueous potassium hydroxide 

Examples of Weak Electrolyte
Tap water ,Carbonic acid ,Acetic acid ,Ammonium hydroxide ,Citric acid ,Oxalic acid 

Examples of Non-Electrolyte
Chemically pure water ,Alcohol ,Kerosene ,Aqueous sugar solution ,Carbon disulphide 





Tidak ada komentar:

Posting Komentar