Learning science is more than just learning the facts of science and learning the skills and concepts necessary to understand those facts. Science is also about investigating nature to find out how things work. The nature of science is that no conclusion that we draw can be trusted unless it can be verified by experiment. But coming up with just the right experiment to perform, and having the skills necessary to perform it, can be a challenge. This is science at its most creative: how do we write a testable, possible explanation (a hypothesis) and then test it conclusively? In this activity you will practice and extend your skills as a scientist.
Your teacher will demonstrate an experiment in which something interesting and/or unexpected happens. You will discuss the experiment as a class and perhaps witness it again with additional instructions. Then you will attempt to re-create the demonstration. After you do this you will work with a partner to come up with possible explanations. First, anything will do but you will ultimately need to narrow down your choices to just those you can test and rule out by observation and experimentation. Follow the procedure below and keep careful notes in your lab notebook of your procedures, hypotheses, and conclusions. Check in frequently with your teacher to be sure you’re on track.
Possible Demonstrations and Extensions
Light a small piece of wood or paper. Drop it into a flask. Let it burn out and then quickly cover the top with a tightly fitting piece of balloon rubber. Explain why the rubber is pulled into the flask, making a tight seal.
Extension: try burning a piece of wood or paper and then without moving anything, do it again. Explain why the new piece will not burn.
Generate a gas (CO2, but don't say this) by reacting baking soda and vinegar in a tall flask or beaker. Gently pour the vessel over the flame of a burning candle so that it goes out. Why does the candle go out?
Extension: blow out the candle, use a lighter or lit match to re-light the candle by putting the flame into the stream of smoke from the extinguished candle.
Turn a flask or cup (without a pour spout) upside down while full of water, holding a piece of paper or plastic over the lip of the vessel. The water does not fall out.
Extension: do the same thing but with a piece of porous plastic screen.
Light a candle. Fill a small paper cup with water. The flame will not burn the paper cup when the cup is full of water.
Extension: Try it with a wet piece of paper towel held in tongs or forceps. It burns and smolders while the cup didn’t.
Set a candle in a shallow dish of water. Light the candle and then cover it with a glass container which seals at its mouth by being covered with the water. The candle goes out and then the water level rises: it has to do with heat expanding the air inside the container and not with using up the oxygen.
Extension: Try using a timer to mark down the sequence of events. Also, try heating the container with hot water and leaving out the candle.
Use a spring scale to weigh small objects. Then weigh them again suspended in water. Ask students to come up with a mathematical way to predict how much the object weighs when suspended in water. Use large rubber erasers, lab flask stoppers or anything dense enough to sink in water. Items with very small volumes might be difficult to use if typical classroom balance precision is all that is available. If necessary, provide objects with specific, whole-number volumes (in cm3 if using g and mL). Or provide masses with regular shapes (coins, cylinders, cubes, etc.) which have a calibrated mass: borrow them from a physics teacher or bring in a roll of nickels or quarters.
Alternatively, weigh the item on a three-beam balance submerged in water, then weigh the item on the balance while it is submerged in water and suspended from a string. When the mass of the beaker and the water are subtracted the mass in the first case is the mass of the item. The mass measured when the item is suspeded from a string will equal only the mass of the water that has been displaced. Ask students what the rule is that governs how much mass is measured. Also ask them whether the mass is changing when it is in water.
Extension: Provide a supply of saturated salt water, which has a density of 1.1 g/mL. Prior to allowing experimentation have students carefully work out what they predict will happen with the same object when suspended in water and salt water.
Show students how to measure the mass lost from the total mass of a container of vinegar and a container of baking soda when they are mixed and the CO2 escapes. Ask them to determine for a constant amount of vinegar the maximum mass that is lost and to find out how much baking soda is required for this. Ask them what they would have to do to make more carbon dioxide. Ask them to figure out how many grams of carbon dioxide they get for each gram of baking soda.
Before trying these with students make sure you understand them completely. Try them yourself and attempt to create your own definitive experiments/observations to prove your answer.
Watch the demonstration. Carefully note details of the procedure. Carefully observe what happens. Discuss with the whole class and share your observations. Write down others’ observations when they add to what you know. Ask questions of your teacher. You are no longer a student but a scientist about to commence an investigation. Try to think like one.
Work with a partner to write (each in your own lab notebook) what is happening in the demonstration and identify the variables that affect the outcome.
Perform the demonstration yourself. Have your partner do it, too. Try some variations and in general play with the materials to see what you can find out. Your teacher may provide you with an extension activity which expands upon the basic demonstration. Investigate this along with the original demonstration. Write down additional observations and ideas that you have about what’s going on.
Discuss what you've seen so far with your teacher and your partner. Brainstorm and be creative. Identify the variables that matter. Write them down. Write statements in the form: “If (my explanation or hypothesis) is true, and I observe the results of (the experiment I design), then (my hypothesis is supported/refuted).” The key to writing a good hypothesis is that you will know what experimental outcome will prove it wrong.
Once all groups have had a chance to get to this point your teacher will call you together for a group discussion so that the class can work together to refine their experimental procedure. After doing this, take the resulting experimental statements and investigate them in the lab.
Design your experiments with care, being sure to abide by lab safety and best laboratory practices.
Carefully carry out your experiments and write down detailed observations and measurements, as appropriate. In your lab notebook record your actual procedure: not what you planned to do but what you actually did.
Reflect as you work: does the result of this experiment support the hypothesis or does it refute it? Is the result of the experiment even relevant to deciding the truth of the hypothesis. Write down a brief reflection in your lab notebook.
If necessary, devise other “If...and...then...” statements, consider possible experiments, consult with your teacher, and then proceed to further your investigation with additional experiments. Remember, you are trying to find a way to prove your hypothesis wrong. Evidence that you cannot prove it wrong is the only good evidence in its favor.
As this process winds down for the various groups in the room your teacher will call the class together for another discussion. Be prepared to share your experiments, your results, and your analysis. In particular, evaluate the usefulness of the observations you made: can they support or refute the hypothesis? Also, be ready to evaluate the hypothesis itself: is it the best hypothesis for investigating this demonstration?
Write a short informal report of your work. Include the following as separate paragraphs:
Include one or more original drawings or photographs which illustrate your work in the lab and/or how you came to your conclusions. Your written work should refer to your drawing/photo at least once.
Display your collected data in a professional format. For example, if you have sets of related numbers then put them in an organized table with clear labels and units. If you have experiments without numerical data then find a way to display your results clearly in a table.
Describe the demonstration you investigated. Include the extension activity, if appropriate. Give enough detail that a reader could perform the demonstration given the right materials. Do not try to explain what is happening or why it is happening.
Give your final hypothesis (or hypotheses) as a “if...and...then...” statements.
What experiments did you perform? Describe them in terms of the physical actions taken.
Hypothetically, what experimental outcome would have proven your hypothesis (or hypotheses) wrong?
Give a good explanation of what is happening in the demonstration and why it is happening. Provide evidence for your explanation using your observations and/or data.
Parts of the text on this lab will
not print out. This is by design. The parts that won’t print are
notes for teachers. Students don’t need those notes and they are
automatically excised from the printout.
This lab was written and designed by Mr. Keller but he used ideas he found in the following article:
Moore, J. C. (2012). Transitional to Formal Operational: Using Authentic Research Experiences to Get Non-Science Students to Think More Like Scientists. European J. of Physics Education, Special Issue 2012, 1-12. Questions specific to the buoyancy lab Sample report for the buoyancy lab.