Because there is so much information packed in this unit, we’re going to split chapter 7 and work on it over 2 weeks.
Textbook Reading: For lesson 8, please read Chapter 7, pp. 205- 217 (Sections 7.1-7.5).
As we learned from the oscillating reaction in Lab 6, chemical reactions are more complicated than simply reactants forming products. In this TED Video called If molecules were people…. you will see chemical reactions from an interesting new perspective.
((Psst: let me know if you like this video, because TED has a number of high energy, fun videos about chemistry like this.))
How do you know if there even has been a chemical reaction? Unfortunately you don’t see arms moving to the face like in the video. But you can look for the evidence:
- Color change
- Formation of a solid
- Formation of a gas
- Heat absorption
- Heat emission
- Light emission
Once we establish there has been a chemical reaction, now we also need to make sure the chemical equations we use are balanced. Section 7.4 has specific information about how to go about balancing an equation.
If you are still not clear on balancing equations after reading the text, or if you would like to see it presented in a different way, you might want to try this A Beginner’s Guide to Balancing Equations video from Bozeman Science.
Did you find the colored molecules helpful?
Solutions and solubility are briefly introduced in this chapter, but will be covered more completely in Chapter 13. Because we are going to be doing some experiments with solutions in lab, let’s go through some basic vocabulary.
The solute is the smallest part of a solution, or the substance being dissolved.
The solvent is the larger part, or the part doing the dissolving.
A solution is a solute dissolved in a solvent.
Miscible means two substances that can mix, and particularly that they can form solutions in any proportion. That means that both substances can be present as the smaller portion or as the larger portion.
By the way, immiscible simply means two substances that can’t mix.
What is the difference between saturated, unsaturated, and supersaturated? Here’s a quick video that really explains clearly:
Recrystallization involves making a supersaturated solution and then adding more solute. This causes the solute to fall out of solution in the form of pure crystals.
Finally, what is the effect of temperature on solutions?
You probably have direct experience trying to add sugar to a cold drink versus a hot drink. Isn’t it easier to stir in sugar and have it dissolve quicker when the liquid is warmer? Solids in general are more soluble at high temperatures and less soluble at low temperature.
(image pubic domain)
As you can see from the graph, however, not all salts follow this general trend. Each salt will have its own solubility curve of how much of the substance will dissolve into the solvent at a given temperature.
Hope you found that helpful. Please let me know if you have any questions!