Standard II, Objective 1

Biology

Standard II, Objective 1

Title: Properties of Water

Description: Students visit a series of stations to learn about water’s properties of heat capacity, pH, capillary action, cohesion, adhesion, surface area/evaporation, surface tension and as a solvent.

Time needed: 60-90 minutes

Materials: listed by station below

Procedures:

1. Set up the stations before class and label them clearly. A description of each station is below. Two of each station will prevent students having to wait long for a new station.

Another option is to do each station as stand alone experiment over a series of days. Each takes about 10-15 minutes.

2. Have the students start in groups of 3-4 at different stations and move when they are done with each. The student directions for each station are also below.

3. Discuss the results after students finish and before they begin the analysis questions.

Station 1: Heat Capacity

Materials: two glass beakers (label A and B), two thermometers, water, hot plate, stopwatch or clock with seconds hand.

Students will add 50 mL of tap water to beaker “A” and nothing to “B”. They will heat both to 30 degrees C and then time how long it takes them to cool to 25 degrees C.

Station 2: pH

Materials: pH paper (any type that measures both acids and bases), weak acid, weak base, beaker, water, stirring rods or wooden splints

Students will add a few drops of acid to the water, test it and then try and get it back to neutral.

Station 3: Capillary action

Materials: capillary tubes, small beakers with different liquids (water, vinegar, salt water, sugar water) metric rulers

Students will test each substance for its ability to travel up the capillary tube.

Station 4: Cohesion, adhesion, surface tension

Materials: penny, dropper or pipette, water, pepper or paper dots from papercutter

Station 5: Surface area and Evaporation

Materials: paper towel, drinking straws, 3 graduated cylinders. Prepare the “leaves” the night before. The paper towels are twisted into the straws. The leaf with the large surface area needs to have a longer piece of paper towel than the medium. The medium needs to be longer than the small. The water will evaporate much more rapidly off the large leaf, emptying the graduated cylinder more rapidly

Station 6: Water as a Solvent

Materials: small beakers or dilution trays, various chemical substances (such as salt, sugar, baking soda, potassium nitrate) rubbing alcohol, water

Station 7: Water Density & Temperature

Materials: Density tank, hot water & cold water, & colored ice

Station 8: Water Density & Buoyancy

Materials: Tall glass or beaker, oil, water, corn syrup, lego piece, Styrofoam piece, metal nut

Properties of Water Name______per___date___

Introduction: Water composes about 70% of most living things and is essential to live as we know it. Water has properties that make it useful in living things. In this series of activities you will experiment with the properties and apply them to how they influence life.

Question: Name as many properties of water as you can:

Procedures:

1. Listen as your teacher describes the location of the 6 stations you will visit. You will work in a group and travel from station to station together.

2. Each station contains directions on how to perform each test. Follow them carefully and write down your data. You may have time to start answering the questions or you may need to move on quickly to the next station.

3. As you finish, start or continue to answer the questions for each. Write a conclusion that contains one sentence about each property.

Station 1-Heat Capacity

Data: time for air to cool______time for water to cool______

Analysis:

1. Heat capacity describes the ability of a substance to gain and lose heat energy. How is water’s heat capacity different than that of air?

2. How might the heat capacity of water affect living things?

3. If our cell were full of air instead of water, what problem would we have in maintaining homeostasis in our body temperature?

Station 2-pH

Data:

Analysis:

1. How are acids related to bases?

2. Living things can tolerate only a narrow range of pH, near 7 or neutral. What does this experiment show about changing pH?

3. Our body has a group of chemicals called buffers that help keep pH in the correct range. Why is this necessary?

Station 3: Capillary Action

Data:

Analysis:

1. Rising up the capillary tube requires the liquid to stick to the sides of the tube (adhesion). Another factor, cohesion makes the liquid molecules want to stay together. Which liquid had the most adhesion? Why so you think so?

2. Which had the most cohesion? Why do you think so?

3. In a tree, capillary action can pull water to enormous heights. What would happen if one of the substances you tested were in the place of water?

Station 4: Cohesion, Adhesion and Surface Tension

Data: 1 2 3

Drawings:

Analysis:

1. Which test shows the property of surface tension? Why?

2. Which test shows adhesion? Why?

3. Which test shows cohesion? Why?

Station 5: Surface Area and Evaporation

Data: water left in cylinder A______cylinder B______cylinder C______

Analysis:

1. Which “leaf” was largest? Which had the most water evaporate?

2. Write a sentence that compares the amount of evaporation with the size or surface area of a leaf:

3. What size leaves would you expect desert plants to have?

Station 6: Water as a Solvent

Data:

Substances (dissolved? Yes/no)

Analysis:

1. Which was a better solvent water or alcohol?

2. Do water and alcohol look different? Smell different?

3. Alcohol is composed of non-polar molecules, water is composed of polar molecules. Why might a polar solvent (the water) be better at dissolving most substances?

Station 7: Water Density and Temperature

Data: Draw what happened in the tank.

Description of the tank:

1.  How does the density of cold and warm water compare?

2.  How does the density of ice compare to water?

3.  Describe what happened as the ice melted and explain why you think it happened in terms of density.

4.  Why is the density of ice important to life on Earth? (think oceans & lakes)

Station 8: Water Density & Buoyancy

Data:

Draw the results in the beaker: Observations of beaker:

1.  Explain why the liquids layered the way they did.

2.  Why did the objects go where they did in the water?

3.  How is water’s density important for living things?

Conclusion: (one summary statement for each station)