The Quality of Science Labs

Both types of observations have different purposes, but they ultimately come together to create the knowledge we have of the world today.  ~Katie                

Beginning two labs of the year, "Lab Techniques" and "Observations in Scientific Inquiry", initiate chemistry students into the two sides of data collection: quantitative data and qualitative data. Our first lab gave the students practice into using measurement tools of chemistry, specifically the mass balance and the graduated cylinder. Dry starch was massed in a weigh boat, added to a beaker with 50 mL of water, stirred, decanted into a second beaker, then filtered, the filter paper dried and massed. Finally, students conduct calculations to determine how much starch was "lost" during all these steps. Rather a sneaky choice for a product to track since starch is sticky so product loss will be substantial, but it drives home the need for precision in measurements and care in lab techniques. 

The second lab was all about making qualitative observations. Copper chloride was added to water and observed for ten minutes. Aluminum foil was then dropped onto the solution and observed for five minutes, after which the solution was stirred vigorously and then filtered. Finally, the filtrate was added to 6M hydrochloric acid and observed for ten minutes. Students were required to make a minimum of 24 observations during this lab experience. Because this is the beginning of the year, students were not expected to understand what happened, and were directed to make just observations -- no inferences or assumptions.  A blank page was left in their lab journals for further notes when they begin to understand the chemistry involved.

To tie the two labs together and emphasize how both types of observations must be recorded, students were asked to write a paragraph discussing the qualitative and quantitative data in terms of the labs that they did. In closing, here are two sample responses, one in partial form:

Quantitative and qualitative observations are two very different things. A quantitative observation includes specific numbers and measurements of a substance. For example, in the density lab with the tin foil, we had to measure the length and width of the tin foil, and then figured out the density, thickness, and volume. These observations all contained numbers so they are quantitative. A qualitative observation includes specific physical traits such as color and size. In the observations in scientific inquiry lab, we had to record the color of the water with copper chloride added and how the color of the water changed. We also had to record the color of the tin foil when we put it in the solution. These observations are more about physical traits so they are qualitative. ~Paige

            A qualitative observation is an observation that can be described. This could be the size or color or the looks of a physical change. A qualitative observation is an observation that involves numbers such a measurements. The reason that qualitative observations are so important is because they can describe a change that is going on and what it looks like. No measurement is going to be able to tell this. In the most recent lab I did, Observations in Scientific Inquiry, I had to do an experiment and make qualitative observations about it. I had to describe the color of the water, whether or not it was bubbling, and what the tin foil seemed to be doing in the solution. Things changed a lot so I had to write down a lot of observations. The reason a quantitative observation is important is because it shows the measurements of something and can help to find out other things about the thing that is being observed. . I took the metal pieces and recorded the mass by weighing them on a balance.... ~Connor

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