PART I. How Much Do You Know About Water

The Wonders of Water!

PART I. How much do you know about water?? Directions: If the statement is true write a “T” in the space to the right. IF THE STATEMENT IS FALSE rewrite the statement to make it true in the space below the statement.

1. Water gets smaller when it freezes.

2. Water is polar because most of it is located near the poles of the planet.

3. Because water is polar it is a good solute.

4. Most of the water in the world is unusable because it is saltwater.

5. Water has the ability to “climb” upward.

PART II. Properties of Water Directions: Read each paragraph below, and make a 1-2 sentence summary for each paragraph on the side. Use a complete sentence. Then complete the questions below and the crossword puzzle, based on the reading.

Water is one of the most important molecules in the world! So, what are the properties of water that make it so unique and necessary for living things? When you look at water, taste and smell it - well, what could be more BORING? Pure water is colorless and has no taste or smell. But, it’s the hidden qualities of water make it a most interesting subject. Let’s zoom into the chemical and physical properties of water.

CHEMICAL PROPERTIES OF WATER The structure of the water molecule gives water unique properties. Water is a polar molecule, which means that it has a region with a slight negative charge (the oxygen atom), and a region with a slight positive charge (the hydrogen atoms). The oppositely charged regions of water molecules interact to form hydrogen bonds. A hydrogen bond is an attraction between a slightly positive hydrogen atom and a slightly negative atom. Hydrogen bonds are responsible for several important properties of water. • High specific heat: Water resists changes in temperature; it must absorb a large amount of heat energy to increase in temperature. • Cohesion: The attraction among molecules of the same substance is called cohesion. Cohesion due to hydrogen bonds makes water molecules “stick” together. • Adhesion: The attraction among molecules of different substances is called adhesion. Water molecules “stick” to many other materials because of hydrogen bonds.

Many compounds that are important for life dissolve in water because of its polarity. Water is the largest component of cells’ interiors, and chemical reactions in the cell take place in this water. When one substance dissolves in another, a solution is formed. The substance present in the greatest amount is called the solvent. Substances that are present in lower amounts and dissolve in the solvent are called solutes. Polar solvents, such as water, dissolve polar molecules and ions. Because of this water is consider to be a universal solvent.

When some substances dissolve in water they break up into ions. A compound that releases a hydrogen ion (a proton) when it dissolves in water is an acid. Bases are compounds that remove, or accept, hydrogen ions. A solution’s acidity, or its hydrogen ion concentration, is measured on the pH scale. An acid has a low pH (pH below 7) and a high hydrogen ion concentration. A base has a high pH (pH above 7) and a low hydrogen ion concentration. Organisms must maintain a stable pH. Even a small change in pH can disrupt many biological processes.

PHYSICAL PROPERTIES OF WATER Water is a weird molecule. Water is the only thing on Earth that is naturally found in all three states of matter -- liquid, solid (ice), and gas (steam). One thing that is strange and unique to water is that when it freezes and becomes solid, it actually gets less dense and lighter. Most things become heavier when they become solid, but not water! That is why solid ice floats in liquid water.

Because water is “sticky” and is held together by hydrogen bonds, it can still hold things heavier than itself on its surface. This strength is called surface tension. For example, there are some insects that can walk on water because the hydrogen bonds of the water are strong enough to keep the water molecules together.

PART III. Questions & Crossword Puzzle DIRECTIONS: Use the reading above to help you solve this crossword puzzle. 1. Explain why water is a polar molecule? ______2. How do hydrogen bonds form? ______3. What are the two parts of a solution? ______4. What types of molecules dissolve easily in water? What types do not dissolve easily in water? ______5. What does pH mean? ______

6. The polarity of water allows it to most substances. Because of this, it is referred to as the .

7. Water molecules “stick” to other water molecules. This property is called .

8. Water molecules “stick” to other materials due to its polar nature. This property is called

9. Explain how waters high specific heat is beneficial for living organisms?

Property of Water Explanation of Property Importance for Life Cohesion

Adhesion

Universal Solvent

Less Dense as a Solid

High Specific Heat