1. Define the terms solution, aqueous solution, solute and solvent and give and example of each.
2. State examples of 5 types of solutions -- solid/solid, solid/liquid, liquid/liquid, gas/liquid, gas/gas.
3. Describe the role of solvation in the dissolving process and use the rule "like dissolves like" to predict the solubility of one substance in another.
4. Explain the difference among saturated, unsaturated, and supersaturated solutions.
5. Obtain information from a solubility curve (graph of grams of solute vs. temperature in a given amount of solvent).
A solution is a mixture of two substances. There are two parts, the solute (typically the lesser amount) dissolved in the solvent (typically the greater amount). Different types of solutions and examples include:
1. Solid dissolved in solid -- one example of a homogenous (even) mixture is an alloy, where different metals are mixed -- yes, they have to be melted, but once cooled down you have a mixture of two metals.
An example of a heterogenous (uneven) mixture would be the carbon center of a wooden pencil.
2. Solid dissolved in a liquid -- this is the major focus in solution chemistry, and I will talk about concentration work in later posts.
A quick example is sugar (solute) dissolved in water (solvent). To increase the solubility (ability to dissolve) in the solvent, increasing the amount of solvent and increasing temperature are typical methods.
To speed up dissolving, agitating (stirring) the mixture is very useful, and increasing the surface area of the solute aids as well. An easy comparison is the surface area of a sugar cube versus the surface area of the smaller "cubes" in granulated sugar.
3. Liquid dissolved in liquid -- this is also a focus in the study of chemistry.
A method of separating a liquid mixture is by fractional distillation which depends on the boiling points of the components of the mixture.
Several textbooks have a diagram of a fractional distillation column used for separating the components of crude oil.
4. Gas dissolved in a liquid -- this is a mixture students are very familiar with b/c many drink carbonated beverage (soda) so it helps to remind students of how they keep their soda from going flat -- keep on the cap (keeping on the pressure) and keep the soda cold (lower temperature increases the solubility of a gas in liquid).
5. Gas dissolved in a gas -- air is a very useful example. Here is one graph of the composition:
One method of separating a liquid mixture is using a separatory funnel Two solvents are used, a polar solvent and a nonpolar solvent. Since polar and nonpolar solvents don't mix (think oil and water), it's a very simple way to divide solutes based on polarity. One phrase used to remember this difference is "like dissolves like" -- polar dissolves polar and nonpolar dissolves nonpolar.
I didn't use a separatory funnel until college level study (organic chemistry), but here is a brief video (less than 4 minutes) about how to use a separatory funnel:
A saturated solution typically has some extra undissolved solute at the bottom. By the way, this is an example of a solution equilibrium and the solute particles are constantly precipitating and dissolving. I'll talk about that later.
A solution that has more solute dissolved at the temperature is called supersaturated. It is an unstable solution and it doesn't take much to disturb the system.
Here is a 10 minute video about preparing a supersaturated solution for demonstration purposes; it also includes a few other examples:
The information of several solutions can be contained on a solubility curve, which is a graph of grams of solute (y-axis) dissolved in 100 g of solvent versus temperature (x-axis). Most of the lines are increasing (solid solutes) but sometimes the line is decreasing (gas solute).
Here is an image that shows how a solubility curve can be read, that the line plots the saturated solution, any point below is an unsaturated solution, and any point above the line would be for a supersaturated solution.
There is a file of worksheets associated with NYS Regents Chemistry in entry #9 of the Teaching Resources on this website.
Here is a class worksheet based on a given solubility curve:
A lab possibility is for the student to develop a solubility curve based on laboratory data. Here's one example:
Remember to wear eye safety goggles and rubberized aprons! Be careful with laboratory thermometers! They can roll off the table and break!
*I'd love to hear from you! Your feedback would really help me to focus on your needs, so write to me! Simply click on the "Contact" tab.
Check out my lab book "Chemistry on a Budget" at amazon.com:
Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
Have a good end of the week!