Factors Affecting Conductance

 Factors Affecting Conductance


1. The number of ions present

This depends upon the strength of the electrolyte ( whether strong or weak) and the concentration of the electrolyte. Salts such as NaCl and KCl are completely dissociated in solution and strong acids such as HCl and H2SO4 are probably completely ionized in aqueous solutions. For this reason they exhibit fairly high conductance over the whole concentration range.
For weak electrolytes such as CH3COOH, concentrated solutions consist mainly of undissociated molecules and hence low molar conductance. As dilution increases, dissociation increases and this is complete at infinite dilution.

2. The speed of the ions under a Potential Gradient

Ionic speeds are usually determined at unit potential gradient. For example if there are two electrodes placed 4cm apart, then to obtain a drop of 1 volt per cm it would be necessary to apply 4 volts between the electrodes. Other factors being equal, the lighter the ion per unit charge the faster it moves under unit potential gradient, hence the better its conducting power.

3. Interionic Attraction

At high concentrations ions in solution tend to form an ionic cloud especially in the case of strong electrolytes. The cations attract the anions and there is repulsion between ions of the similar charge. On increasing dilution inter-ionic attraction forces are reduced and hence the speed of the ion increases.

4. Hydration

The extent of hydration of an ion will affect its speed in solution. The hydration includes not only that water actually bound to each ion in definite amounts but also the oriented solvent atmosphere that the ions tend to establish around them.

5. Temperature

A rise in temperature leads to a decrease in the viscosity of the solution which leads to an increase in the velocity of an ion.




Table 2.: Molar Conductance of Electrolytes in Aqueous Solutions at 25°C/-1cm2mol1
Concentration mol dm-3
NaCl
KCL
H2SO4
CH3COOH
NH3
0.0000
0.0005
0.001
0.01
0.10
126.5
124.5
123.7
118.5
106.7
149.9
413.1
399.5
336.4
250.8
429.6
413.1
399.5
336.4
250.8
390.7
67.7
49.2
16.3
5.2
271.4
47.0
34.0
11.3
3.6



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