TEACHER NOTES Properties of Water Key Concept The properties of water make it a unique substance on Earth. Skills Focus observing, inferring, predicting Time 60 minutes Materials (per group) plastic cup tap water 3-cm square of metal window screening dark food coloring paper towel scissors 250-mL beaker distilled water hot plate thermometer, metal spoon salt hot pad wax pencil Alternate Materials If possible, use alcohol thermometers rather than mercury thermometers. Advanced Preparation You may want to form the screening containers for Part A ahead of time. Consider setting up separate stations for Parts A, B, and C. Teaching Tips Dark food coloring will make the water movement easier to see. Students can complete Part C while waiting to observe the results from Part B.
Name Date Class Properties of Water Pre-Lab Discussion Water is the only substance on Earth that commonly exists in all three states solid, liquid, and gas. Water also has some other unusual properties. In this investigation, you will examine some properties of the substance that covers most of Earth s surface. 1. What are three properties of water that are caused by the attractions among water molecules? 2. Why can water dissolve so many other substances? Problem What are some of the unique properties of water? Materials (per group) plastic cup tap water 3-cm square of metal window screening dark food coloring paper towel scissors 250-mL beaker distilled water hot plate thermometer, metal spoon salt hot pad wax pencil Safety Review the safety guidelines in appendix A of your textbook. Handle the thermometer carefully. If it breaks, do not touch it and immediately tell your teacher. Use tongs or a hot pad when handling hot objects. Always wear safety goggles when heating objects.
Name Date Class Procedure Part A: Surface Tension 1. Fill a plastic cup three-fourths full with tap water. 2. Bend up the sides of the window screening to form the shape Figure 1 shown in Figure 1. Be careful of any sharp edges on the screen. 3. Predict what will happen if you place the screening on the water s surface. Explain your reasoning. 4. Carefully set the bottom of the container flat on the surface of the water in the cup. Do not touch the water with your hand. Observe whether the container sinks or floats. Record your observations under Observations. Part B: Capillary Action 1. Put about 2 cm of tap water in the plastic cup. Add 2 or 3 drops of food coloring to the water. 2. Cut a strip of paper towel about 1 cm wide. Drape it over the lip of the cup so that one end is in the water. See Figure 2. 3. Predict what will happen to the paper strip. Explain your reasoning. Figure 2 4. Set the cup aside. After about 20 minutes, observe the strip of paper towel. Record your observations under Observations. Part C: Changing States 1. CAUTION: Put on your safety goggles and apron. Fill a 250-mL beaker two-thirds full of distilled water. Place the beaker on a hot plate. 2. Heat the water until it boils. Measure the temperature of the boiling water. CAUTION: Handle the thermometer carefully; it is breakable. 3. Let the water cool slightly. Add a spoonful of salt to the water. Predict how adding salt will affect the water s boiling point. Explain your reasoning. 4. Heat the water until it boils and record the temperature of the boiling water in the Data Table under Observations. 5. Repeat Steps 3 and 4 three more times. CAUTION: Use a hot pad or beaker tongs to handle the beaker.
Name Date Class Properties of Water (continued) Observations Part A 1. What happened when you placed the screening on the water s surface? Part B 1. What did you observe about the end of the paper towel that was outside the cup? Part C Data Table Boiling-Point Temperature Distilled water Distilled water + 1 spoon of salt Distilled water + 2 spoons of salt Distilled water + 3 spoons of salt Distilled water + 4 spoons of salt Analyze and Conclude 1. Explain your observations in Part A based on what you know about the surface tension of water. 2. Explain your observations in Part B based on what you know about capillary action. 3. How does dissolving salt in water affect the temperature at which the water boils?
Name Date Class Critical Thinking and Applications 1. What do you think would happen if you put a penny on the screening? Give a reason for your answer. 2. If you cut off a centimeter from the bottom of a celery stalk and put the cut end into water colored with blue food coloring, in about an hour the stem would be streaked with blue. Explain what happens in terms of capillary action. 3. When some people cook vegetables, they add salt to the cooking water. They say this makes the vegetables cook faster. Are they correct? Give a reason for your answer. More to Explore New Problem Does dissolving salt in water change the freezing point of the water? Possible Materials Consider what materials you will need. Write a list of your materials. Safety Handle thermometers carefully. Wear your safety goggles and apron. Procedure Write a procedure you could follow to find the answer to the problem. Have the teacher approve your procedure before you carry out the investigation. (Hint: You do not necessarily need to make salt water freeze to answer this question.) Observations Make a data table and record your observations. Analyze and Conclude 1. How does dissolving salt in water affect its freezing point? 2. Why do some communities spread salt on icy roads in winter?