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General Chemistry Principles, Patterns, and Applications, 2011

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are drawn using a “best-fit” approach; that is, data points are not connected as a series of straight-line<br />

segments; rather, a smooth line or curve is drawn that provides the best fit to the plotted data.<br />

The independent variable is usually assigned to the horizontal, or x, axis (also called the abscissa), <strong>and</strong> the<br />

dependent variable to the vertical, or y, axis (called theordinate). Let’s examine, for example, an<br />

experiment in which we are interested in plotting the change in the concentration of compound A with<br />

time. Because time does not depend on the concentration of A but the concentration of A does depend on<br />

the amount of time that has passed during the reaction, time is the independent variable <strong>and</strong><br />

concentration is the dependent variable. In this case, the time is assigned to the horizontal axis <strong>and</strong> the<br />

concentration of A to the vertical axis.<br />

We may plot more than one dependent variable on a graph, but the lines or curves corresponding to each<br />

set of data must be clearly identified with labels, different types of lines (a dashed line, for example), or<br />

different symbols for the respective data points (e.g., a triangle versus a circle). When words are used to<br />

label a line or curve, either a key identifying the different sets of data or a label placed next to each line or<br />

curve is used.<br />

Interpreting a Graph<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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