Solutions & Solubility (Water & its Properties)
The Solutions Unit is broken into pages that roughly forly the standards. The topics can be found at the right. Pratice problems in some topics can be found on the page for that topic. A breakdown of the topics and what is covered in each is listed below.
- This unit is under construction - Ccontent here is limited, but practice problems work.
- The Special Properties of Water. Water has unique properties generally raleated to its polarity, that make it important in both chemistry and biochemistry. These properties include its unusually high heat capacity, surface tension, cohesion, and the fact that as a solid (ice) it is less dense than as a liquid, which is opposite to almost all other substances. It is called the "universal solvent" (not really true) because its polarity allows it to dissolve many polar compounds. Colligative properties are referenced in another topic.
- What is a Solution? Solutions are homogeneous mixtures made up of (at minimum) one solute and one solvent. Terms are defined here and some general descriptions are given.
- Solubility - What will dissolve and what will not. This is related to both polarity and properties of ions. Solubility rules are discussed and can be used to determine whether-or-not a reaction in an aqueous solution will occur. The term, "Like-Dissolves-Like" is explained in terms of polarity.
- Calculating Concentration. This unit focuses on the primary unit of concentration, molarity. Molarity is the number of moles of solute dissolved per liter of total solution. There are other units of concentration such as mole fraction and molality that are referenced but included in a separate topic. Unlimited practice problems are provided for this topic
- Calculating Dilutions. Solutions are not "Strong" or "Weak" - they are "Concentrated" or "Dilute". Diluting is a means of converting a concentrated solution into aa more dilute solution by the addition of water. Students should know how to take a high molarity, concetrated solution and make a more dilute solution for use in the lab. This topic discusses the calculations to do this. Unlimited practice problems are provided for this topic
- Electrolytes vs. Nonelectrolytes. Electrolytes are substances that when dissolved in water affect the conductivity of the water. To be conductive, charge must flow. In a wire that is becuase of a sea of elecctrons. In a solution it is caused by charged particles, or ions. How well a substance conducts electricity depends mainly on how many ions exist in the solution.
- Saturation of Solutions. A solution can be unsaturated, which means more solute can dissolve, saturated, which means no more solute can dissolve, or supersaturated, which means that too much solute is dissolved. The last condition is typically unstable and solute will precipitate out of solution quickly if given the opportunity. Saturation typically depends greatly on temperature, and in the case ofdissolved gases, on pressure.
- Factors Affecting Solubility and Rates. This topic covers the factors that affect the rate at which substances dissolve, such as temperature, surface area and agitation, and factors that affect how much of a substance will dissolve (which is also covered in the previous topic on saturation).
- Supplemental Information not required in the Texas Essential Knowledge and Skills (TEKS) for chemistry include: "Other units of concentration", such as molality and mole fraction, and "Colligative properties of water". Colligative properties are those properties that depend on the amount of solute and not the nature of the solute and include, Freezing Point Depression and Boiling Point Elevation.
Practice Worksheets, PowerPoints & Videos
Intro To Gas Laws Worksheet (and the KEY)
PhET Simulation about gas molecules (requires Java)
The practice workshsheets above are original and have keys available. Also available are links to resources on other sites, including simulations and videos produced by others