Chapter 3 provided us with the tools necessary to balance chemical reactions and use stoichiometry to calculate the amount of reactants and products that are consumed or produced in a chemical reaction.
You will use these same concepts from Chapter 3 as we will investigate the properties and the reactions that take place in solutions with water as the solvent, or aqueous solutions.
4.1 Reactions in Aqueous Solutions Overview
When certain compounds dissolve their resulting solutions can conduct electricity. These solutions are referred to as electrolytic solutions, or electrolytes, as the solute dissolved produces ions in solution. Electrolytes can then be categorized as strong, weak, or non-electrolytes.
In addition to being able to conduct electricity, when ions come into contact with each other in solution it is possible that a precipitate might form. We can use a set of guidelines to predict precipitate formation know as the “Solubility Guidelines.”
4.2 Precipitation Reactions
Once we have determined if a precipitate forms we need a convention to express the reactions happening in solution. A Net Ionic Equation represents the ions and molecules directly involved in metahesis reactions.
4.2 Metathesis and Net Ionic Equations
In addition to having electrolytic properties, solutions can be classified as acidic or basic, which in later sections of the text will be related to the pH of a solution. We can classify solutions as acidic or basic and we find that their classification is also related to electrolytes and you will be responsible for knowing the strong acids and strong bases.
4.3 Acids and Bases
Once an understanding of acids and bases was established, chemists began to be curious and started mixing them together. A neutralization reaction is defined as a reaction occurring when an acid and a base are mixed together.
4.3 Neutralization Reactions and Gaseous Products
It is common to observe a reaction where the charges (or more accurately oxidation states) of a reactant change in becoming a product. In doing so, an electron must be gained or lost. The question is where does this electron come from or where does it go? Electrons cannot be created or destroyed, but they can be transferred from one species to another. We need to set up a bookkeeping system to keep track of where these electrons are coming and going and the system that chemists use to do this is assigning oxidation numbers.
4.4 Oxidation Reduction Reactions and Assigning Oxidation Numbers Part 1
4.4 Oxidation Reduction Reactions and Assigning Oxidation Numbers Part 2
Once the rules are established for oxidation-reduction reactions, we can see the relationship between the guidelines given in the video above and the reactions we observe in the lab. The following video shows you show examples of how to assign oxidation numbers in chemical reactions.
4.4 Assigning Oxidation Numbers Example Problem
Acids can be very corrosive, but they will not dissolve all metals. The “Activity Series” is a guideline allowing a chemist to predict whether an oxidation-reduction reaction will occur. The ability to properly interpret the Activity Series of Metals in Aqueous Solution gives the reader a great deal of information regarding the reactivity of metals in solution.
4.4 Oxidation of Metals by Acids
The properties of an aqueous solution are highly dependent upon the concentration of the solution. There are various ways to represent the concentration of a solution. For example, the concentration of alcohol in a beer is typically represented by % alcohol by volume, where liquor is commonly represented by proof. When chemists communicate concentration with each other they do so using units of Molarity, which is moles of solute per liter of solution.
4.5 Concentrations of Solutions
4.5 Concentrations of Solutions Example Problem
A common practice performed in larger labs is to purchase or prepare solutions at high concentrations then dilute them. When these dilutions occur the volume of the solutions change, but the number of moles remains constant.
Notice that when representing concentration units they are dependent upon moles and the same set of stoichiometry guidelines govern reactions in solution. There is one extra bit of complexity that comes into play as we need to keep track of the volume of the solutions we are analyzing.
4.6 Solution Stoichiometry and Chemical Analysis
A common laboratory technique to determine the concentration of a solution is called a titration. In a titration a standard solution, with a known concentration, is titrated against a solution of unknown concentration and the concentration of the unknown solution can be calculated.