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Paper Topic:

Chemistry Lab Report #2

Electrolytes and Non - Electrolytes

Candice Joseph

February 20 , 2007

1 . Purpose

The experiments were carried out for measurement of conductance of strong electrolytes , weak electrolytes and non electrolytes in aqueous solution . The purpose was to measure and predict electrical conductance of these different types of materials namely strong , weak and non electrolytes and also to distinguish between strong and weak acids based on their electrical conductance in aqueous solution

2 . Introduction

All materials offer resistance to electrical current and the electrical resistance (R ) is defined by following well-known

equation (1 (Ohms . However , different materials offer different amount of resistance to the electrical current through them . Physically this means , high current can be obtained through these materials by applying relatively smaller voltage if electrical resistance of the material is less and vice - versa

Inverse of resistance R i .e . 1 /R is known as Conductance generally denoted by ? and its unit is Sieman S 1 ?Certain materials are electrical insulator i .e . do not allow electrical current through them in solid state , but they become electrical conductors in their aqueous solution . This is primarily because , these materials dissociate in their constituent ions , which are free to move under applied voltage or electric field and hence facilitate current through their aqueous solution . The conductance of the aqueous solution of different materials depends on the degree to which they dissociate in the aqueous solution Those , which dissociate completely have highest conductance and termed as strong electrolytes like NaCl , KCl , HCl etc , those which dissociate to relatively much lesser extent have relatively much smaller conductance like CH3COOH , NH4COOH etc . and those which do not dissociate at all have conductance approaching zero and are termed as non electrolytes like sugar . Some examples of dissociation reaction in aqueous solution for strong and weak electrolytes are following

Strong electrolyte (KCl

Na Cl-

The arrow indicates that the reaction goes to completion in right direction

Weak Electrolyte (CH3COOH


The arrow pointing in both directions implies that species of both left and right side are present in the solution and there is dynamic equilibrium between these species

Electrical conductivity of an aqueous solution depends on the number of ions and type of the ions as type of the ions determines their mobility Besides conductivity depends on concentration of the solution as for weak electrolytes number of ions is dependent on concentration of the solution . Equivalent ionic conductivity of different ions at infinite dilution i .e ?o is listed in table 1 below (1

Table 1 : Equivalent Ionic Conductivity at Infinite Dilution ?o (10-4 S-m2 /mol

Ion 1 /3Al 3 1 /2Ca 2 H K Na Cl- C2H3O2- 1 /3PO4-3 ?o 61 .0 59 .47 49 .65 73 .48 50 .08 76 .31 40 .9 69 .0 From the table we find that H ion has highest equivalent ionic conductivity . This is because H ion has highest mobility due to its smallest size . There is an apparent contradiction in the sense that Na has lower equivalent ionic conductivity...

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