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Graphing In Chemistry

Graphing In Chemistry. Year 11 DP Chemistry R. Slider. Why Graph?. In Chemistry, we make frequent use of graphs to provide a visual representation of data. This will often make the data easier to interpret. We can easily see trends or relationships. We can predict unknown values.

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Graphing In Chemistry

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  1. Graphing In Chemistry Year 11 DP Chemistry R. Slider

  2. Why Graph? • In Chemistry, we make frequent use of graphs to provide a visual representation of data. • This will often make the data easier to interpret. • We can easily see trends or relationships. • We can predict unknown values. • Line graphs for continuous data. • Bar graphs for non-continuous data. Fig1. Favourite Subject

  3. What is a Graph? • A graph is a visual representation of numerical systems and relationships. • For example, a straight line can be represented by the equation to the right where: • y = the value on the vertical axis • x = the value on the horizontal axis • m = the slope of the line (Δy/Δx) • b = the y intercept • What is the slope of this line and what would the slope represent?

  4. Components of a line Graph Title Error Bars (not shown here) Reasonable scale Key (if needed) Labels (units) Smooth lines Big enough: (takes up more than ½ the graph For detailed rules on constructing a graph click HERE

  5. Plotting a line Graph • there are two axes - horizontal (called the x-axis) and vertical (called the y-axis), • a point on the graph is denoted by an ordered pair (or coordinates (e.g., (3,8)) where: • the first number refers to horizontal position on the x-axis, • the second number refers to vertical position on the y-axis, • sometimes the ordered pairs are listed in tabular format with headings that correspond to the labels on the axis • the two axes intersect at point called the origin with coordinates (0,0), • the reason that we plot data is so that we can more easily observe trends or behaviour of the data • (modified from Anderson and Swanson, 2005)

  6. Types of linear Line Graphs Fig. 2 Inversely proportional Fig. 1 Directly proportional Directly proportional graphs show variables that are directly related to one another while inversely proportional graphs show an inverse relationship (e.g. P = 1/V as in Boyle’s Law.)

  7. Non-Linear line graphs • These non-linear graphs show exponential relationships – growth (right) and decay (left)

  8. Line of Best Fit • When presenting data, it is most likely that the point-to-point connection of the data points will not result in a smooth curve or straight line. • Often you will need to draw a “best fit line” to show the overall relationship that is present. This will allow you to make predictions about other data points or to measure gradients. • Look at the graph below. How would you draw a best fit line? • The line should represent the general trend as close as possible • There should be as many points above as there are below the line • Excel and Logger Pro will draw best fit lines for you.

  9. Bar/Column Graphs • Bar graphs can also be used in scientific reporting. • We choose to use a bar graph when we have non-continuous data. That is, there is no reason to show data between two points on the graph. • Notice that it would make no sense to draw a line between testosterone and prolactin as there is no data between them (i.e. non-continuous) • If there is only one set of data, we use a bar graph (i.e. no x and y data) • You must still fully label your bar graph.

  10. What’s wrong with these graphs? A B D C

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