Chapter 4: Chemical Quantities and Aqueous Reactions

4.2 Reaction Stoichiometry: How Much Carbon Dioxide

This section is all about how you use the balanced equation to determine the different relationships between the amount of reactants and the amount of products. The key point in this is that all these relationships are based upon the stoichiometric coefficients (the numbers in front of the compounds in the balanced equation) and the number of moles. We will use these relationships throughout the year.

Percent Yield. This is another variation on the basic stoichiometry problem. In the basic problem, we assume that everything works out perfectly. Guess what, in real life it does not. Reactions don't produce as much as we calculate they should (the theoretical yield). Remember percent is part/total * 100. Chemists and chemical engineers work VERY hard to try and increase the percent yield for reactions. If you can increase the yield for a process, your boss will be very happy.

4.3 Limiting Reactant, Theoretical Yield, and Percent Yield

The first twist on the basic stoichiometry problem is what happens when one of the reactants is in excess. If you have one slice of cheese and 10 loaves of bread, you can still make only one cheese sandwich. If you are careful when solving stoichiometry problems, you won't make this mistake. If you are not careful, you will make a mistake with this type of problem. So, be careful.

4.4 Solution Concentration and Solution Stoichiometry

Molarity is one unit used to describe concentration (we will use others latter in the course). It will be used lots and it is a KEY CONCEPT. Remember molarity=mole/liter. This is a three variable equation, you will use it to solve for moles, molarity, or liters. It is used for lots of problems. Remember it is the connection between volume of a solution and the number of moles. Like molecular weight is the connection between mass and number of moles.

4.5 Types of Aqueous Solutions and Solubility

This section explains what happens to ionic compounds in solution. The model shown in Figure 5.1 of an ionic compound dissolving is really important. Always keep in mind what happens when ionic compounds dissolve. For this semester we will stick with reactions of strong electrolytes, where things dissolve completely. The concept of a week electrolyte is also introduced, these are compounds that dissociate a little bit. This complicates what happens in solution and you will learn how to deal with these complications next semester. For now, you can assume that things are either strong electrolytes or nonelectrolytes. Figure 5.4 shows solubility rules for ionic compounds in water. If you know these rules, you can predict what will happen to an ionic compound in water. You can answer the question (will it dissolve). You MUST know this. If you do not, you will probably fail every exam this semester, and several next semester. So get out your notecards and get to work.

4.6 Precipitation Reactions

After you know the solubility rules, it will be easy to predict when a precipitation reaction will occur. The general setup is that you take two different soluble compounds and dissolve them seperately in water. These two solutions are then mixed together. IF there is a combination of ions that is insoluble in this new mixture, they will form a precipitate. These reactions can be written several different ways; the overall equation (where things are written as compounds), the ionic equation (where all ions are written as ions); and the net ionic equation (spectator ions that do not react are dropped from the ionic equation).

4.8 Acid-Base and Gas-Evolution Reactions

You will need to be able to identify and name acids. Memorize the strong acids listed in table 5.2. Recognize bases, usually metal hydroxides ammonium is the common exception.

We will do LOTS of work with acid base reactions this year, so get to know what they are all about. There are several different "theories" of acid base reactions that explain what is happening. Writing out ionic equations will be very helpful for determining what will react. In general if an acid and a base react, they produce a salt and water.

4.9 Oxidation-Reduction Reactions

This chapter will not be discussed until second semester.