Last week, we did another lab, Elephant’s Toothpaste. Now, the class should learn how to write a report and draw conclusions. Lab design, creating hypotheses, and drawing conclusions are tedious to teach. Here is the lab rubric I use for Chemistry. Last week Elephant’s Toothpaste uses hydrogen peroxide, yeast, and dish soap. The kids varied the number of grams of yeast and timed the soapy solution as it reached the top of the test tube. Here goes the lesson.
1. What is the hypothesis? A hypothesis has two parts: null and alternate
a. The null hypothesis for this lab is, “There is no relationship between the number of grams of yeast and the time it takes for the soapy solution to reach the top of the test tube—or The time of reaction is independent of the amount of yeast.”
b. The alternate or alternative hypothesis (your best guess) is, “The more grams of yeast, the shorter the time for the soapy solution to reach the top of the test tube—or The more yeast, the faster the reaction.”
2. The next section is background material. Yeast contains the enzyme, catalase, in the cell’s peroxisome organelles. Hydrogen peroxide is a common waste product in cells. (Waste is bad.). The catalase breaks down hydrogen peroxide. In this lab, the yeast is allowed to bloom and produce catalase, which breaks down hydrogen peroxide. Kids can write the background in quotes—but must cite the source.
3. Next is the chemical reaction for this experiment., if pertinent. Hydrogen peroxide breaks down in the presence of catalase into water and oxygen. Students may write the balanced reaction neatly in pen or 2 H2O2 —— H2O + O2
4. On to the materials. The materials include the following items: test tube rack, six test tubes, a test tube holder, scoopula, one disposable, graduated, transfer pipette, a 50 mL graduated cylinder, a 10
mL graduated cylinder, cell phone stop watch, three plastic beakers, one digital thermometer, a tray or trough for overflow, a digital scale, one weigh boat, 20 grams of yeast, 30 mL dish soap, 200 mL water, and one craft stir stick. Note the grammar! Numbers ten or fewer are spelled and greater are written in Arabic character, one and 50. Please note a colon follows a noun. The sentence above is an example of the use of third person, present tense, active voice, and indicative mood.
5. The next section, results, includes the data, ideally a table or chart. The student may write the results. For example, the results are five grams of yeast produces suds in 4.9 seconds.
6. The procedures must be discussed step by step. The controlled variables are the water temperature, the amount of water, dish soap, and hydrogen peroxide. The independent variable is the number of grams of yeast. The student completes three trials. For each trial, the student adds one milliliter of yeast solution to one milliliter of dish soap and five milliliters of hydrogen peroxide in a 25 mL test tube. The student measures each trial with a stopwatch to assess the time the soapy solution travels to the top of the test tube. The student records each trial in a table.
7. The discussion section follows the data. This section has any observations or mistakes. The student notes that 25 grams of yeast causes an eruption of suds to quick to measure. This is the point
the student determines if the results support or refute the null or alternate hypotheses. It is not
unusual for the results to refute both. Here, the child should use the Claim Evidence Reasoning approach to describe the results. The claim is that more yeast results in a faster reaction. The student’s data table should indicate shorter intervals. The reasoning is that more yeast produces more catalase, consequently breaks down more hydrogen peroxide.
8. Lastly is the conclusion. My standard conclusion is this one, “More trials are indicated.” “More study is needed to determine the results support the alternate hypothesis.”
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