Lesson 2: Water and Its Characteristics
Getting Started
In this lesson, you will continue to explore the unique features of the hydrosphere as well as the qualities of the hydrosphere's primary component, water. Understanding these characteristics will help you to understand the uniqueness and importance of water for life.
You will also study polarity, cohesion, and surface tension in this lesson. Polarity is the presence of two different charges (positive and negative) on an object, cohesion is the attraction between two molecules, and surface tension is a property of the surface of a liquid that allows it to resist an external force. For this lesson, you will conduct investigations to further your understanding of each of these characteristics and how polarity, cohesion, and surface tension influence the behavior of water.
You will also study polarity, cohesion, and surface tension in this lesson. Polarity is the presence of two different charges (positive and negative) on an object, cohesion is the attraction between two molecules, and surface tension is a property of the surface of a liquid that allows it to resist an external force. For this lesson, you will conduct investigations to further your understanding of each of these characteristics and how polarity, cohesion, and surface tension influence the behavior of water.
Stuff You Need
- Protecting Earth's Water Supply by Ron Fridell
- 10-12 quarters, nickels, and pennies
- 2 eggs
- bubbles or detergent solution
- candle (kit)
- funnel (kit)
- saline solution, rubbing alcohol, clear diet soda, or other solution* (Activity 2 - Option 2)
- small clear cups (kit)
- tall drinking glass
- vinegar
* - denotes an optional material that may or may not be needed
Ideas to Think About
- How does the chemical nature of water influence its behavior?
- What would happen if water did not have the chemical properties it has?
Things to Know
- Cohesion is the attraction between two molecules of the same type; adhesion is the attraction between two molecules of different types.
- Polarity is the presence of two different charges (positive and negative) on an object.
- The polarity of molecules allows cohesion to occur.
- Surface tension is a property of the surface of a liquid that allows it to resist an external force.
- Surface tension is caused by the cohesion of like molecules and is responsible for many of the behaviors of water.
Skills
- Observe, collect, organize, and analyze data. (S)
- Analyze evidence to explain observations, make inferences and predictions, and develop the relationship between evidence and explanation. (S)
- Use oral and written language to communicate findings. (LA)
- Analyze and evaluate information from a scientifically literate viewpoint by reading, hearing, and/or viewing scientific texts, articles, and events in the popular press. (S)
- Analyze the unique properties of water: polarity, cohesion, and surface tension. (S)
Introducing the Lesson
In this lesson, your child will continue developing an understanding of the characteristics associated with water. She will proceed in activities that focus on observing polarity, cohesion, and surface tension and how these characteristics impact the behavior of water.
As your child makes observations and increases her understanding of the characteristics of water being studied, she will be further developing the ability to make connections between what she sees in an activity and her day-to-day life. The challenge for your child will be to continue developing inquiry skills such as observation and inference. These skills are important in all scientific investigations and are present in the claims and evidence that scientists have used and continue to use to develop and shape investigations. As in the previous lesson, the focus is for your child to understand how polarity, cohesion, and surface tension are present on the water planet and how they can mean the difference between life and death on a global scale.
As your child makes observations and increases her understanding of the characteristics of water being studied, she will be further developing the ability to make connections between what she sees in an activity and her day-to-day life. The challenge for your child will be to continue developing inquiry skills such as observation and inference. These skills are important in all scientific investigations and are present in the claims and evidence that scientists have used and continue to use to develop and shape investigations. As in the previous lesson, the focus is for your child to understand how polarity, cohesion, and surface tension are present on the water planet and how they can mean the difference between life and death on a global scale.
Materials: Protecting Earth's Water Supply by Ron Fridell
Today you will focus on polarity, cohesion, and surface tension. Do the following:
— Read pages 4-8 in Protecting Earth's Water Supply.
— Read the web articles "Water Properties" and "Adhesion and Cohesion of Water" from the United States Geological Survey (found at the following web links)
— Watch the video "How Polarity Makes Water Behave Strangely" by TED-Ed.
Use the video and readings from the book and web articles to answer the following questions:
Web Link
Web Link
Questions
- What is cohesion and why is it important?Cohesion is the attraction between two molecules. There is cohesion between water molecules. Cohesion is important because it prevents water from evaporating quickly.
- If there was no cohesion between water molecules, what would happen?Lack of cohesion would lead to fast rates of evaporation. The Earth's surface would be much drier.
- What is adhesion and how is it different from cohesion?Adhesion describes how water molecules stick to other molecules. Cohesion describes how water molecules stick together.
- What causes the polarity of water?The positive and negative charges of the hydrogen and oxygen atoms that make up water molecules make water molecules be attracted to each other.
- Why does water form drops rather than thin sheets?Molecules of water attract one another strongly enough to make them clump together into rounded droplets rather than spread out in a thin film.
- What property of water allows some bugs and objects to stand on top of it?Surface tension, which is caused by the cohesion of water molecules, is a property of water that allows it to resist external forces. This property allows some objects to sit atop the surface of the water.
Web Link