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Different Graph Types

• Bar• Point• Pie

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Why use different kinds of graphs?

• Bar graphs give a clear picture/visual of different categories of data for ease of comparison.

• Pie graphs show what part/percentage of the whole sample (pie) each portion supplies.

• Point graphs (most useful in chemistry) reflect continuously changing and measured data and how they relate to each other mathematically. Two types – curve (point to point) and best fit line.

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Very Important Graph Parts

• Title• Appropriate scales (bar and point) on both X

axis and Y axis. • X axis and Y axis labeled with appropriate

units (bar and point)

Look back at the sample graphs on slide 2 – does each graph have the VIGPs???

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Point Graphs

• Title should tell the reader what has been measured and graphed. Write in “Y” versus “X” form .

• X axis (independent variable) – data that changes on its own.• Y axis (dependent variable) – changes in response to what X

did.• Number scale on each axis should be large enough for

measured data to fit within the minimum and maximum scale values. Can you increase by 1s, 2s, 5s, 10s? Do not increase values randomly – scale should show a pattern and be consistent.

• Each axis should have a label that describes what was measured and the unit with which the data are measured.

• If multiple point graphs use the same axes and scales, a key should be used to identify the graph for each set of points

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Temperature

(°C)

Time (seconds)

10 20 30 40 50 60 70 80 80 100

50

40

30

20

10

60

Temperature versus time in a chemical reaction

Title

Y Axis (vertical) and consistent scale

X Axis (hortizontal) and consistent scale

Y Axis label and (units)

X Axis label and (units)

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Examine this point graph and then answer each of the accompanying questions on your Graphing Exercise worksheet.

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Best Fit Line Point Graphs

• Once all data points have been graphed, use a ruler to “find a path” or best fit line through the plotted data (not doing point to point).

• Best fit line should come as close to as many data points as possible, even if the “path” doesn’t intersect the data points. Choose carefully and try several options before committing and drawing the line.

• Best fit line is an graphic average. What mathematical relationship does it average? Calculate slope using 2 points from the line (not the plotted data points).

• “rise” (Y) over “run” (X)• Slope usually has units.

Units are: Y units X units

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12

xx

yyslope

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Notice not all the data fit on the line. Data points are plotted first, and then the best fit line is drawn.

Where the best fit line is drawn is guided by finding the best fit through the data points – most of the data points are close to, if not directly on, the best fit line.

“Bad” data are then obvious, because they don’t fit anywhere near the line.

Bad data? It’s farthest from best fit line, but not by much

Notice how these 2 points “split the difference” and are the same distance (but on opposite sides) of the best fit line. Ideal!

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Examine this point graph and then answer each of the accompanying questions on your Graphing Exercise worksheet.

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Bar Graphs• Not often used in Chemistry• Should have the VIGPs although 1 scale is more description than

measured data• Represents information that is static - that means it’s not changing,

it represents only 1 moment in time, instead of one variable responding to a change in another

• Visual• Each bar occupies a “column” – columns may be separated or not• A key identifies each bar when there are multiple categories of data• Bar graphs can be done vertically or horizontally

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Title

Y axis and label with units

X axis and label

Y axis scale

X axis “scale”

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Examine this point graph and then answer each of the accompanying questions on your Graphing Exercise worksheet.

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Pie Charts• Pie charts aren’t used very often in

Chemistry, because the data represented in it is static

• Very visual and newspapers like using them for this reason. Can be “intact” or “exploded”

• The pie chart should still have a clearly labeled title

• When doing a pie chart, each part of the pie is labeled or a color key is provided that identifies each part. Percentages should be clearly identified

To create a pie chart, you’ll need a calculator, protractor, and compass.

• Make sure all data are converted into a % of the total information – check to make sure all %s add up to 100..

• Convert each % into a matching number of degrees, since circles total 360 degrees – check to make sure all the degrees total 360.

• Use the compass to draw a circle and the protractor to draw a radius for the circle

• Using the first radius as a base, measure the first part’s degrees. Mark the limit of this part with a new radius and then continue until all parts have been measured and marked

• If you’ve done everything correctly, the last piece of the pie should meet the first piece

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Title

Key

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Examine this point graph and then answer each of the accompanying questions on your Graphing Exercise worksheet.

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