Solutions are classified as homogenous mixtures consisting of a solute(material being dissolved) and a solvent (material doing the dissolving) and exist as a solid, liquid, or a gas.
We will devote most of our time and effort discussing the liquid solvent and solid solute method of making solutions as the main activity of this unit will involve the growing of crystals from solutions.
Not all materials can be dissolved in a substance and are said to be insoluble in that substance. If a substance can be dissolved it is said to be soluble and the solution may be saturated, saturated, or supersaturated.
Unsaturated solutions can hold more solute for that temperature and pressure while saturated solutions can no longer hold any more solute under the same conditions. When a solution contains more solute than it can normally hold at that temperature and pressure, we say it is supersaturated and is very unstable. A saturated solution is needed for the growing of crystals which we will grow from an aqueous solution of sodium chloride and water.
First let’s do some experiments to see how the size of particles, temperature, and agitation affect a substances rate of solubility. In the lab manual for “Physical Science” by Louise Nolan and published by D.C. Heath and Company 1987, a good lab is available. (sample at end of unit)
After completing this exercise we will construct a solubility curve with grams of solute/100 ml water vs temperatures of 20 degrees centigrade, 40 degrees centigrade, 60 degrees centigrade, 80 degrees centigrade, and 100 degrees centigrade.
We will use potassium chlorate for our solute and mass 80 grams before adding it to the 100 ml of water. We will then add the solute to the water until it becomes saturated (particles begin to settle out) and mass the remaining solute to determine the amount added. Plot the number of grams used over the corresponding temperature and continue this until all mass/temperatures have been recorded.
(figure available in print form)
Now that that we have concluded our basic study of matter, we will move to the topic of crystals.