# Lesson 1: The Hydrosphere

## Day 2

### Activity 2: Water and Its Behavior

Materials: blue food coloring (kit), graduated cylinder (kit), green food coloring (kit), measuring cup, red food coloring (kit), scale (kit), yellow food coloring (kit)
For this activity, you will find the mass and density of four solutions and record your findings in a data table.

First, create a Data Table as shown below.
 Data Table Solution Name Solution Mass (grams) Solution Volume (mL) Solution Density (grams/mL) Tap Water 100 25% 100 50% 100 100% 100
Next, you will create 100 milliliters of each of the four different solutions, similar to how you created them when you made the ice cubes. In this case, however, you will be creating exactly 100 milliliters of each solution.
First, set out your four clear plastic containers (the ones labeled "Tap Water," "25%," "50%," and "100%"). Then follow these instructions:
 Salt Solutions for Measuring Mass and Density Salt Percentage Instructions Food Coloring 0% Pour 100 milliliters of tap water into the "Tap Water" container Add 2 drops of green food coloring and mix well. 25% Mix 25 milliliters of 100% solution with 75 milliliters of water, and put this solution in the "25%" container. Add 2 drops of blue food coloring and mix well. 50% Mix 50 milliliters of 100% solution with 50 milliliters of water, and put this solution in the "50%" container. Add 2 drops of yellow food coloring and mix well. 100% Pour 100 milliliters of "100% Salt Water Solution" into the "100%" container. Add 2 drops of red food coloring and mix well.

#### Measuring Mass

Before measuring the mass of each solution, use one of the empty clear cups to "zero" the scale. Place an empty cup on the scale. (Be sure to use a cup that is the same size as the ones that contain your solutions.) Then adjust the knob on the top of the scale until the dial reads exactly zero.

Next, measure the mass of each of your solutions and record them in your data table. (Be sure you are reading the mass in grams and not ounces.)

Note that the volume of each solution should be 100 mL.

For your consideration: Is there a difference in the mass of the substances? If you were to pour two solutions together (assuming that they do not mix), what would you expect to see?
Check your child's answer for the "For your consideration" question, "Is there a difference in the mass of the substances?"

Answer: Yes, each substance has a different mass. The differences may be very small, but they are there. Also, ask him to consider why the masses are different. (The salt in each solution adds mass.)

Answer: The more dense solution (the one that has the greater mass than the other) would "settle" on the bottom of a container while the less dense solution would settle on the top.

#### Determining Density

In the table you created, you have recorded the mass and volume of the liquids measured. Now use those two measurements to calculate density. To determine the density of each solution, use the following formula:
 Density = Mass/Volume
Your child's mass measurements and density calculations should be similar to the values shown in the table below. (Your child's numbers may not match these exactly because he may have slightly different measurements for the mass of each solution.)
 Activity 2 Table Solution Name Solution Mass (grams) Solution Volume (mL) Solution Density (g/mL) Tap water 100 100 1 25% solution 105 100 1.05 50% solution 110 100 1.1 100% solution 120 100 1.2

### Activity 3: Density Variables

Materials: eye droppers (kit), small clear cups (kit)
In this activity, you will explore different factors that can affect solution density. Ask a parent which option to complete.
Both options of this activity will require your child to think about how different factors affect density. Option 2 is more involved and time-consuming than Option 1 as it requires your child to observe two variables. Assess how much time you have to devote to this activity and then tell your child which option to complete.

Note: If you choose Option 2, your child will use the directions from Option 1 to fill out the table in Option 2.

#### Option 1

You will conduct an investigation to determine the movement of water and how density influences this movement. During the experiment, you will use the table at the top of the "Movement Based on Density" page to record information.

For this activity, you will use the ice cubes you made yesterday. Follow these steps:
1. Fill four clear cups or glasses with room-temperature tap water.
2. If the solution froze to form ice cubes, place an ice cube in one of the cups of tap water. Record your observations in the "Observation 2 (Top)" column of the table on the "Movement Based on Density" page. (For solutions that froze to ice cubes, you will leave the "Observation 1 (Bottom)" column blank.)
3. If the solution did not form ice cubes, fill an eye or medicine dropper with the solution. Be sure to wipe down the outside of the medicine dropper. Insert the medicine dropper into the tap water and gently squeeze out the colored solution with the tip of the medicine dropper at the bottom of the glass. (See the "Water Density" illustration below.) Observe what happens and record this in the "Observation 1 (Bottom)" column of the table.
4. For solutions that did not form ice cubes, you will again fill a medicine dropper with the solution and wipe down the outside, but this time you will place the tip of the medicine dropper at the top of the glass (just above the water) and squeeze out the solution. Observe what happens and record this in the "Observation 2 (Top)" column of the table.
Be sure to repeat Step 2 (for solutions that froze to ice cubes) or Steps 3-4 (for solutions that did not freeze completely) for each solution.

Once you have completed the activity, answer the "Things to Ponder" questions at the bottom of the activity page. Your answers may be as short as one sentence or as long as a brief paragraph.
Student Activity Page
Water Density

Observation One (Bottom): The saline solutions that did not freeze should remain at the bottom of the cup. Eventually, the solution will disperse throughout the cup. Because the saline is denser than the tap water, however, the food coloring should remain at the bottom of the cup. If the food coloring does disperse, it will take awhile. You may want to let your child put the cups to the side and see what happens over the course of time.

Observation Two (Top): Observe the water slowly move towards the bottom of the cup as the ice cube melts or as the solution enters the tap water. While the 100% solution is the most dense, it is not likely that the students will observe a difference in how quickly the solutions settle.
Questions to Ponder:

How does the density of the water influence its behavior?
The denser water sinks to the bottom or remains at the bottom.

Explain how the density of water influences its movement in the oceans (consider the readings on density currents) and other bodies of water.
Density causes currents in the ocean. Heavier waters sink and lighter waters rise to the top. The movement of these different density currents influences the movement of nutrients in the oceans and also influences climate by influencing water temperatures. The same process occurs in other bodies of water such as lakes and ponds.

#### Option 2

In this activity, you will experiment with a new variable. The new variable will be the temperature of the water that you place the saline solutions in. You will also be able to experiment with the saline solutions at different temperatures.

Additions to activity for Option 2
Use the directions from Option 1 to complete the table on the "Making Guesses" sheets. In addition to the observations from the first option, you will also be able to guess or hypothesize about what the outcome will be.
Repeat the steps from Option 1 using one of the following changes:
• Use chilled tap water
• Use heated saline solutions and room-temperature tap water
• Have both the saline solutions and water at the same temperature
• Have both the saline solutions and water chilled
• Have both the saline solutions and water at room temperature
• Have both the saline solutions and water heated
You may also want to consider mixing different saline solutions or come up with additional changes.

For each entry in the "Solution Combination & Temperature" column, be sure to fill in the "Expected Outcome" box before you perform the experiment.

NOTE: For each additional variable used, you will need to add three to four new rows to the table. Refer to the "Sample Table: Option 2" graphic as an example.
Sample Table: Option 2
Student Activity Page
Student Activity Page
In developing the chart, your child will want to create room for a lot more data to be collected. He can carry out the Option 1 trial as well as additional trials that involve changing temperature variables (tap water is chilled versus at room temperature, for example). See "Sample Table: Option 2" for what your child's chart might look like. The sample table is based on using two different temperature variables for the activity.

Skills in developing observation tables and learning to work with experimental variables will progress through the unit. At first the experiments will have a lot of structure (created tables, very explicit directions and illustrations), but as your child progresses through the curriculum, the goal is to have him be able to think through and develop tables that will be beneficial for collecting data and analyzing it.

In general, higher saltwater concentrations and cooler samples will sink faster than lower concentrations or warmer samples; they will also remain at the bottom of the cups longer.

Encourage your child to think about the huge difference in the amounts of water in oceans or lakes compared to the small samples with which he is working. Encourage your child to think critically about what he expected and factors that may have influenced the results.