I’m not a fan of the scientific method. Experimentation doesn’t always take a linear approach. Some experiments have hypotheses and others have a purpose. Still other labs replicate a classic experiment. I loathe trying to construct ‘if than’ statements to govern a lab. Most of the labs completed in Physical Science classes (or any high school, science class ) has a purpose rather than a hypothesis. Here is an entire book about experimental design, which is much messier than the Scientific Process or the Scientific Method.
It is a good idea to teach about experimental design. I use Mummifying Apples to teach experimental design. First, the Egyptians used natron; therefore the experiment includes salt (NaCl, sodium chloride), baking soda, (NaHCO3, sodium bicarbonate), washing soda (NaCO3, sodium carbonate—Arm & Hammer), and Epsom salts (MgSO4*7H2O, magnesium sulfate*heptahydrate). This is a good blend of chemicals to simulate nation. Now comes the hard part. Ask the kids to determine which salts actually draws out water. How can you determine which salt actually does the work? The answer is to design an experiment. This is the independent variable. More in a bit.
It takes time to understand the masses of the apple slices must be the same. The cups must be the same. The mass of salt or salt mixture must be the same. These are controlled variables. You try to control as many aspects of the experiment as possible. We put ours in a box to control light.
There are confounding variables to any experiment: the relative humidity, temperature, cats, anything which could disturb the experiment.
The kids should have a total of 50 g in each cup. I made a chart below. I find numbering the chemicals to be helpful: 1. NaCl, 2. NaHCO3, 3. NaCO3, and 4. MgSO4*7H2O. Be sure to use the same proportions of each chemical.
Now is the time to determine a hypothesis. Which combination will draw out the most water? A hypothesis has two parts: the Null and Alternative hypotheses. The null hypothesis is that each combination will draw out water to the same extent. The alternative hypothesis is that one combination, say 1&2 will draw more water than any other.
The kids should weigh the apples every few days for a ten day period. Teens should keep good records. If they knocked over the contents of a cup or forgot to enter an apple slices, that should be in the notes. Eventually, one Apple slice will weigh the least. Now is the time for a conclusion.
The conclusion should explain whether the results support the null hypothesis, the alternative hypothesis, or neither. Finally, more trials are indicated. Typically, kids put one slice of each combination in a cup, essentially one trial. Three cups for each slice would be better. I just don’t want to spend $50 on one lab.
Here is a lab report as a slide show. Here is an example with the Co-op class data—at least some of it. This is the same process used to build a science fair project. Yes, this is hard! Apple Mummies works for elementary to high school students as a tool to understand experimental design.