Substances, Mixtures and Solubility

A. A substance is matter that has a fixed composition. 1. An element is an example of a pure substance.

a. A substance cannot be broken down into simpler parts by ordinary physical processes, such as boiling or grinding.

b. Only a chemical process, such as burning or reacting with other chemicals, can change a substance into one or more different substances.

2. Water is a substance that is a compound, a chemical combination of two or more elements.

B. Mixtures- combinations of substances that are not bonded together and can be separated by physical processes.

1. Heterogeneous mixtures contain substances that are not mixed evenly and have different compositions in different areas.

2. Two or more substances evenly mixed on a molecular level but not bonded together are called homogeneous mixture or a solution.

C. The substance that dissolves in a solution is the solute; the solvent is the substance that dissolves the solute.

1. A solid that falls out of solution is called a precipitate.

2. Stalactites and stalagmites in caves are precipitates of minerals that were dissolved in water.

D. Solutions can be made of different combinations of solids, liquids, and gases.

1. In a liquid solution, the solute can be another liquid, a solid, or a gas. a. Salt water and sugar water are liquid-solid solutions.

b. Carbonated beverages are liquid-gas solutions. c. Vinegar is a liquid-liquid solution made of water and acetic acid.

2. In a gas-gas solution such as air, the larger amount of gas (nitrogen) is the solvent and the smaller amount of gas (oxygen) is the solute.

3. A solid-solid solution made from two or more metals is called an alloy; sometimes nonmetal elements are included in an alloy.

a. Brass is an alloy of copper and zinc. b. Steel is an alloy of iron and carbon, which makes the steel stronger and more flexible.

Ch What is Solubility A. Water, called the universal solvent, forms an aqueous solution with a solute.

Ch What is Solubility 1. Some molecular compounds share electrons in a nonpolar covalent bond; water is a molecule with polar covalent bonds.

Ch What is Solubility 2. Some atoms in compounds lose or gain electrons and become charged atoms called ions.

Ch What is Solubility 3. When an ionic compound is mixed with water, the different ions of the compound are pulled apart, or dissolved, by the water molecules.

Ch What is Solubility 4. Water dissolves molecular compounds like sugar by separating the molecules and spreading them throughout the water.

Ch What is Solubility B. Substances that dissolve in another substance are called soluble in that substance; substances that do not dissolve in another substance are termed insoluble in that substance.

Ch What is Solubility 1. “Like dissolves like” means that polar molecules dissolve other polar molecules, and nonpolar molecules dissolve other nonpolar molecules.

Ch What is Solubility 2. Nonpolar molecules will not dissolve polar molecules, and vice versa.

Ch What is Solubility C. Solubility - measurement that describes how much solute dissolves in a given amount of solvent at a given temperature.

Ch What is Solubility 1. Several factors, including time, motion, temperature, and contact area, affect the rate of dissolving.

Ch What is Solubility 2. Some solid solutes become more soluble as the temperature of the liquid solvent increases.

Ch What is Solubility 3. An increase in temperature decreases the solubility of gas in a liquid-gas solution.

Ch What is Solubility 4. A saturated solution contains all the solute it can hold under a given condition.

Ch What is Solubility D. The concentration of a solution is how much solute is present compared to the amount of solvent.

Ch What is Solubility 1. Concentrated solutions have more solute per given amount of solvent than dilute solutions.

Ch What is Solubility 2. Concentrations can be stated as a percentage of the volume of solution that is solute.