Students conduct tests to determine common properties of bases.
After completing this tutorial, you will be able to complete the following:
Bases are most commonly defined as substances that increase the concentration of hydroxide ions in a water-based solution. Bases have a pH greater than 7.0, with the strength of the base increasing with the pH value.
Bases usually are clear when in an aqueous solution. In order to determine if a substance is a base, a number of tests can be done. The most common is to place a drop on a piece of litmus paper. Litmus paper is a thin sheet of paper treated with dyes that are extracted from lichens, which may change color in the presence of an acid or base. In the case of a base, both red and blue litmus paper will turn blue.
A useful pH indicator is red cabbage juice. Red cabbage is boiled in water to produce a blue-purple colored liquid. This liquid will change to green in the presence of a base. If a couple drops of a solution are placed into the juice, and the juice turns green, the solution has a pH above 7 and is basic. A chemical indicator, which can identify a substance as an acid or base, is phenolphthalein. If a couple of drops of the indicator are placed in an acidic solution, the solution will remain colorless. If the solution turns pink, it is a base.
Eggshells are comprised of calcium carbonate, which reacts with acids but not bases. If a solution is dropped onto eggshells, and no reaction occurs, the solution is potentially a base.
|Approximate Time||20 Minutes|
|Pre-requisite Concepts||Students are familiar with the concepts of ions, pH, and solutions.|
|Type of Tutorial||Experiment|
|Key Vocabulary||acid, ammonia, base|