26 May 2014

Thinking scientifically about graphing: a classroom exercise for general chemistry

In-Class Activity

Submitted by Jennifer Look, Mercer University
Course Level: 

This excercise explains the basics of drawing graphs for an introductory chemistry class. It give examples of common pitfalls and how to avoid them. Students are guided through graphing a data set, adjusting axes, adding trend lines, modifying legends and adding appropriate labels. The excercise also provides several examples of graphs and asks students to critically evaluate them. 

Learning Goals: 

After completing this activity, students will understand basic requirements for scientific graphing. They will be able to interpret graphs, identify common mistakes, and use Excel 2010 (available in campus computer labs) efficiently to generate graphs. Student will gain experience critically analyzing graphs, and communicating about data interpretation.

Equipment needs: 

Computer, Microsoft Excel 2010

Implementation Notes: 

Students typically work in groups of 3 -4 students. We do this exercise during the third week of our first semester General Chemistry class.

Figure 1  You can put ANY data with an irregular axis here. The graph shown is based on the song “99 problems” which is rather vulgar and misogynistic. I use this because it gets students thinking about how any data, even JayZ lyrics, can be graphed. You don’t need an equation or explanation to look at a relationship. Some years I use a version of the pirate vs global temperature graph from “An Open Letter to the Kansas School Board”, other times I just put rainfall versus year (skipping some years).

Selecting groups I ask the students to line up in terms of how comfortable they are with computers. I give them two examples of "expert" Excel tasks - using a concatentate formula to combine data and using conditional formatting to change cells colors - and have people very comfortable with those tasks stand at one end of the room, and people who aren't sure how to turn a computer on at the other.  Then I ask them to talk to each other and pick a group of people to work with. I explain that the goal is to get everyone to complete the activity within the 75 minute period, so the faster students need to help out the others and everyone needs to help each other stay focussed and on track. 


  • Group selection takes about 10 minutes, including logging on to computers.
  • They have about 5 minutes for reading and brainstorming about section 1 (parts of a graph).
  • Section 2 (graph types) takes the slower groups about 10 minutes.
  • Section 3 (drawing a graph) is fast - only about 2 minutes.
  • Section 4 (axes) is where some of the more proficient groups typically provide a lot of assistance to the others. This typically takes about another 10 - 15 minutes for all groups to complete.
  • Section 5 (lines) takes about 5 minutes, except for groups that get into deep conversations about what is science, and the difference between laws and theories. I love those conversations, but this is an easy section to cut in the interest of time.
  • Section 6 (labels) takes the remainder of the period. Groups submit their graphs as well as the answers to the worksheet questions.


Time Required: 
75 minutes
Evaluation Methods: 

I check in with all of the groups periodically during the activity to make sure they are writing what I consider to be thorough, thoughtful answers to each question. If a group is rushing to get done rather than focussing on understanding, I give them additional tasks. For example, I may ask them to come up with an example for each different graph type (pie, column, line and scatter) where that specific type is the best way to displaythe data. Then I ask the to come up for general rules for each type about when it should and should not be used.

I grade fairly leniently, giving 70% for completion and 30% for correct answers. I have office hours in the computer lab the week we do this, so any students who need extra time can have it. The 30% graded portion breaks down:

Figure 1 discussion 5 pt - If the answer is superficial (e.g. "The presentation is ok") or a not every question is answered, I give partial credit. I do not take off if they say that it is expotential.

Figure 2 & 3 5 pt - Full credit requires correctly identifying the graph types and labelling problems. The large amount of white space in Fig 2 we discuss, but I don't take off points for.

Section 4 fill in the blanks are worth 6 points (correct order and units)

Section 5 law versus theory 4 points. Full credit awarded for answers that communicate effectively about  laws/theories and accuracy/precision. If there is no support ("It's not science, precision") they get no points regardless of correctness.

Section 6 - 8 points for completed, correct graph. 1 point each for meaningful titles/legends for the last 2 graphs.

Evaluation Results: 

I have implemented several variations of this activity over the last several years. The quality of graphs submitted with lab reports throughout the semester has improved drastically. Even though students often have difficulty with the assignment as we do it, having this resource to look back at proves a very useful resource.

Groupwork skills are the part of this assignment that students struggle the most with. Learning to work efficiently as a group is a daunting task, and sometimes group members get left behind or the group does not complete the assignment. Depending on the students, I adjust the assignment for each class. For example, I may have one section of the worksheet be take-home work or give an additional assignment to find a critique a graph from the news. I try to be proactive in spotting and pointing out groupwork issues. If a student is racing ahead without input from the rest of the group, I ask them to teach another student to do something. If a student looks lost, I try to get them to ask questions or contribute to the group on a specific question.

The question most students get wrong is the laws versus theories discussion. The misconceptions that "laws are True" and "theories are guesses" is hard to overcome, even after class discussions.

I have one teaching assistant and 30 students for a 75 minute period, and the vast majority of students have enough computer literacy skills to do a great job on this assignment. However, the students that have never used a computer before are overwhelmed. Identifying these students early in the semester and figuring out how to get help with  this assignment (office hour graphing practice, meeting with a tutor in the computer lab, etc)  lets these students recognize that techology support available and appropriate for this class.

Creative Commons License: 
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