Abstract, Background, Introduction
Solutions in which ions are present can be categorized using the
measurement of conductivity. Ions carry charges and due to this characteristic
there is a direct correlation between conductivity of solutions and the
concentration of ions in solutions. The larger the concentration of ions the higher the conductivity is. In very concentrated solutions there can be interactions between ions that can alter the conductivity of the solutions. Therefore to measure the conductivity of solutions dilute solutions are used because in dilute solutions the interaction between ions can be neglected. In dilute solutions the conductivity is directly proportional to the concentrations of ions. Conductivity can be expressed using the following equation in which κ is the conductivity, l is the distance between the electrodes, A is the surface area of the electrodes, k is the cell constant and R is the resistance.
In subjects like physics electrolyte solutions obey Ohm’s law in which due to potential (U), current (I) is passed through the solution and resistance (R) is equal to R=U/I. In chemistry conductivity is used in place of resistance.
When normalizing the conductivity to one mole of substance the molar
conductivity (Λm) is used. This method is expressed in the following equation in
which ci is equal to the concentration of ions.
For this particular experiment glacial acetic acid was tested. Acetic acid
was chosen because is a weak electrolyte that is ideal for the measurement of
conductivity. When acetic acid is introduced into a solution two types of ions are
produced, hydrogen ions (H+) and acetate ions (OAc-).
HC2H3O2(aq) H+(aq) + C2H3O2-(aq)
The concentration of these ions can be represented by the following equation in
which c is the initial acetic acid concentration and α is the degree of ionization.
For this particular situation the equilibrium constant Ka can be represented as:
Therefore, the conductivity of a weak electrolyte solution is dependent on the concentration of ions which is also dependant on the degree of ionization. The equation for the equilibrium constant can be rearranged to:
Since the conductivity of a solution is dependent on the degree of ionization and the concentration of ions, the following equation hold true for the molar conductivity. is equal to the limiting molar conductivity at zero concentration.
In combining the last two equations the following equation is obtained:
This equation reveals that by plotting 1/ Λm against Λmc, and Ka can be calculated. The goal of this experiment was to create a variety of diluted solutions of acetic acid, measure their conductivity then create a plot of 1/ Λm against Λmc, to obtain the and Ka for acetic acid.