Materials
- water
- white vinegar
- hydrogen peroxide
- corn syrup
- mineral oil
- clear soda
- salt (for solubility)
- pepper (for surface tension)
- sugar (solubility)
- baking soda (solubility/chemical reactions)
- corn starch (solubility)
- wax paper (surface tension, cohesion)
- aluminum foil (to use for chemical reactions)
- Hot and cold water baths (evaporation, condensation, specific heat)
- Ice (density)
- A Scale (mass)
- Paper Clips (surface tension)
- Toothpicks (density, surface tension)
- Food coloring (density)
- Thermometers (temp., phase change)
- pH strips (acidity)
- Liquid soap (surface tension)
- Safety Goggles
- Beakers/Cups
- Petri dishes
- Pipettes
- Glass rods
Procedure
Part I:
1. Present the following situation to the students: You are stranded on a deserted island. You are running low on fresh water. If given six clear liquids would you be able to determine which one is water?
2. Have students brainstorm words and phrases to describe water. Try to get them to use all five senses. List the words on the board. It should prove to be more difficult then they think!
3. Divide the students into groups of 3 or 4. Remind the students that there is no eating/drinking in the lab. Also, remind them that they should never put their nose up to an unknown substance and safety goggles should be worn at all times!
4. Provide each group with the six clear liquids (water, white vinegar, hydrogen peroxide, corn syrup, mineral oil, clear soda) in beakers/cups labeled with the group number and the letter assigned to that liquid. Try to vary which liquid is assigned to which letter for each group. This will add to the mystery and ensure that students are working within their own group. Ask the question - Which one is water?
5. Have the students work with their partners to brainstorm questions they have about the liquids. They should also write out ways to answer these questions. Put out materials that are available to them (see materials list). This should help them decide what to test. The material list above also describes some of the tests that can be conducted. If students are having difficulty determining what to test, you should question them on what they know about water and testing chemicals. Often students determine the tests they would like to conduct after they begin experimenting, this should be encouraged. Each student should write out the questions/procedures on the worksheet provided.
6. Before the students begin testing the liquids, you may need to remind them about ensuring that their experiments are controlled. In other words, there should be only one independent variable while everything else is controlled. Also, remind them that the liquids are a limited supply (after all we're on a deserted island). They should be careful not to contaminate their liquids or cause the whole batch to be useless for future experiments. Adding something to the liquid could potentially change its chemical makeup.
7. At this point, the students may begin conducting their tests. Of course, they will need to record their results in a data table. You should choose whether students will construct their own data or use one provided.
8. At this point, the groups should begin using any of the materials provided to attempt to determine which liquid is water.
9. Following the investigation, students must draw conclusions based on their results. Even if students did not narrow it down to just one liquid, they should describe which liquids they know are not water. Make sure the students are specific and cite their results. Also, have students describe the properties of water that make it different from other clear liquids.
Extensions
- Students could prepare a presentation to explain to the class which one is liquid water and how they know.
- Students could research what would happen to the human body without water.
- Connections to other activities: This activity is related to a lesson that involves students investigating why one should not drink seawater. Students use potato cells to represent animal cells and learn how salt water dehydrates cells faster than not drinking anything at all!
Description
This activity is intended for middle school students following lessons on the properties of water and how they are tested.
- Students are faced with the situation of being stranded on a deserted island and the need to determine which liquid is water so that they may drink it to survive.
- Students will need to make observations and conduct tests necessary to determine which liquid is water.
- Students will discover what they know, and do not know, about the properties of water.
- Students should have an understanding of the following concepts: solubility, surface tension, evaporation/condensation, density, temperature, and acidity.
Assessment
Students may be assessed on:
- Investigation design
- Their conclusions to their investigation and how it related to their results
- Their description of the properties of water that distinguish it from other clear liquids.
Reflections
When selecting materials for this activity be sure to use tonic water that is still highly carbonated!
Be sure that students rely on more than one test before determining a liquid is not water. Do not allow them to just rely on smell. Explain that the smell of water and other substances can be easily tainted with trace amounts of chemicals.
Reference
This activity was adapted from Project Wets' "Water on Zork" activity.
Project WET Curriculum and Activity Guide (1995). The Water course and the Council for Environment.
Time Required
Approximately two 40-minute class periods.
