February 3, 2015
After introducing the concept of “like dissolves like,” sensors can be used to quantify how much solute is dissolved in a solution.
Conductivity is a great tool for quantifying the amount of particular types of solute in a solution. Depending on the type of solute, students can also try to create a linear graph relating conductivity to concentration.
There is a linear relationship between the concentration of an electrolyte and its conductivity.
The first set of data represents a solution with increasing amounts of salt added. Since salt is an electrolyte, the conductivity is linearly related to the concentration. The second set of data represents a sugar solution. Sugar is soluble in water but, as a non-electrolyte, the concentration cannot be related to the conductivity measurement.
Luckily, sugar molecules have a chiral center and are optically active. The amount of optical rotation will depend on the type and amount of sugar present. Using a Polarimeter, you can measure the optical rotation of a variety of sugar solution concentrations.
The Polarimeter measures the light intensity vs the angle of rotation.
The change in optical rotation is linearly related to the concentration of the sugar solution.
Determining the amount of solute in a solution is an important part of any chemistry class. Having the appropriate sensors, and knowing the properties of the solutes and solvents, gives students the tools they need to quantify the concentration of a solution.