Representing Data Chemistry A

Representing Data A goal for most scientists is to discover whether a pattern exists in their data. Graphs help visualize the data and determine if there are patterns present. Tables help organize data but patterns are not that obvious.

“ A picture is worth a thousand words.” Graphing As mentioned before a graph can help reveal a pattern if one exists. Graph = a visual display of data. “ A picture is worth a thousand words.” Three types of graphs: Line, Circle, and Bar graphs.

Circle Graphs (Pie Charts) This graph is sometimes called a pie chart because it is divided into wedges like a pie or pizza. A circle graph is useful for showing parts of a fixed whole. Data is usually represented in percents and the whole circle adds up to 100%

Bar Graph A bar graph is often used to show how a quantity varies with factors such as time, location, or temperature. The dependent variable is on the y-axis. The independent variable on the x-axis. The different heights of the bars show how the quantities vary. A bar graph can be used to compare data.

Line Graphs In this class this will be the graph we will use the most. The points on the line graph represent the intersection of data for two variables The dependent variable is on the y-axis. The independent variable on the x-axis. Because the points can be scattered, we can’t pass a straight line through all them.

Best Fit Line The straight line must be drawn so that equal amount of points fall above and below the line. Best fit line shows the linear relationship between variables and that variables are directly related. The relationship can be further described by the slope

Slope A positive slope, rises to the right. It also indicates that the dependent variable increases as the independent variable increases. A negative slope, rises to the left. The dependent variable decreases as the independent variable increases. Either way the slope of the line is constant.

Slope You can calculate the slope using two data points. Slope = y2 – y1 = Δ y X2 – x1 Δ x The slope is the change in y divided by the change in x.

Interpreting Graphs 1st identify the independent and dependent variables 2nd Look at ranges of data and consider what measurements were taken 3rd decide if the relationship between variables is linear or nonlinear.

4th If the relationship is linear, is the slope negative or positive? 5th If the graph has multiple regions or line, look at one at a time. 6th When points are connected, data considered continuous.

7th Interpolation- reading data that falls between measured points. 8th Extrapolation- reading points that go beyond the plotted data, an estimate.