Properties of WaterProperties of Water

Chapter 2: Section 1Chapter 2: Section 1

SOL 6.5 a,b & cSOL 6.5 a,b & c

How would you describe How would you describe water?water?

What we tend to describe it What we tend to describe it as...as... No colorNo color No tasteNo taste No odorNo odor Plain, ordinaryPlain, ordinary

Chemists think differently!Chemists think differently!

Water is made up of atoms. Water is made up of atoms. 2 hydrogen and 1 Oxygen atom form 2 hydrogen and 1 Oxygen atom form

a water molecule (Ha water molecule (H22O)O)

Hydrogen = slight (+) or positive Hydrogen = slight (+) or positive chargecharge

Oxygen= slight (–) or negative chargeOxygen= slight (–) or negative charge

Polar molecule= a molecule that has Polar molecule= a molecule that has electrically charged areas. Substances electrically charged areas. Substances with polar molecules are called polar with polar molecules are called polar substances.substances.

Water is a polar molecule.Water is a polar molecule.

The positive hydrogen ends of one water The positive hydrogen ends of one water molecule attract the negative oxygen ends molecule attract the negative oxygen ends of nearby water molecules. As a result, of nearby water molecules. As a result, the water molecules tend to stick together.the water molecules tend to stick together.

Question: What makes water a polar Question: What makes water a polar molecule? molecule?

•Because it is a polar substance, water has Because it is a polar substance, water has many unusual properties:many unusual properties:

Surface tension= the tightness across the Surface tension= the tightness across the surface of water that is caused by the polar surface of water that is caused by the polar molecules pulling on one another. The pulling molecules pulling on one another. The pulling forces the surface of the water into a curved forces the surface of the water into a curved shape. It also causes raindrops to form round shape. It also causes raindrops to form round beads when landing on a windshield of a car.beads when landing on a windshield of a car.

Question: Why does water seem to have a Question: Why does water seem to have a “skin” on its surface?“skin” on its surface?

Capillary Action= the combined force Capillary Action= the combined force of attraction among water molecules of attraction among water molecules and with the molecules of and with the molecules of surrounding materials. surrounding materials. Causes water molecules to cling to the Causes water molecules to cling to the

fibers of materials like paper and clothfibers of materials like paper and cloth Allows water to move through materials Allows water to move through materials

with pores or narrow spaces insidewith pores or narrow spaces inside

Question: How does a paper Question: How does a paper

towel soak up water? towel soak up water?

Solution= a mixture that forms when one substance dissolves another. (ex. Solution= a mixture that forms when one substance dissolves another. (ex. Lemonade)Lemonade) The substance that does the dissolving is called the solvent. (in this The substance that does the dissolving is called the solvent. (in this

example= water)example= water)

Solvent dissolves Solute Solvent dissolves Solute (water is solvent and lemonade powder would be (water is solvent and lemonade powder would be solute)solute)

Question: Give me another example of a solution. (not lemonade)Question: Give me another example of a solution. (not lemonade)

Water is often called the “universal Water is often called the “universal solvent” because it dissolves so many solvent” because it dissolves so many substances because it is made up of polar substances because it is made up of polar molecules, which attract other substances molecules, which attract other substances with polar molecules. with polar molecules. It can dissolve sugar, salt, soap, liquids such It can dissolve sugar, salt, soap, liquids such

as bleach and rubbing alcohol, and gases such as bleach and rubbing alcohol, and gases such as oxygen and carbon dioxide. as oxygen and carbon dioxide.

It cannot dissolve oils and wax because they It cannot dissolve oils and wax because they are made up of non-polar molecules which do are made up of non-polar molecules which do not dissolve well in water.not dissolve well in water.

Question: Why is water called the universal Question: Why is water called the universal solvent?solvent?

Water exists on Earth in all three states: Water exists on Earth in all three states: solid, liquid and gas.solid, liquid and gas. The molecules in solid ice are close together and The molecules in solid ice are close together and

form a rigid structure. (cold temperatures <0 form a rigid structure. (cold temperatures <0 degrees C)degrees C)

In liquid water, the molecules move more freely In liquid water, the molecules move more freely and the water takes the shape of its container. (0 and the water takes the shape of its container. (0 to 100 degrees C)to 100 degrees C)

The molecules in gaseous water vapor move The molecules in gaseous water vapor move very freely and spread out to fill a space. (> 100 very freely and spread out to fill a space. (> 100 degrees C)degrees C)

Question: Describe the structureQuestion: Describe the structureof molecules in liquid water.of molecules in liquid water.

Temperature is a measurement of the Temperature is a measurement of the average speed of the molecules. Ice has average speed of the molecules. Ice has the lowest temperature/speed and the lowest temperature/speed and Gaseous water vapor has the highest.Gaseous water vapor has the highest.

Energy must be added or released for Energy must be added or released for water molecules to change state:water molecules to change state: Evaporation is the process by which molecules Evaporation is the process by which molecules

at the surface of a liquid absorb enough at the surface of a liquid absorb enough energy to change to the gaseous state.energy to change to the gaseous state.

Condensation is the process by which a gas Condensation is the process by which a gas changes to a liquid.changes to a liquid.

Question: What is it called when water vapor in Question: What is it called when water vapor in the air changes to a liquid on a glass? the air changes to a liquid on a glass?

When water cools below 4 degrees C the When water cools below 4 degrees C the molecules begin to line up in a grid-like molecules begin to line up in a grid-like crystal structure which takes up more crystal structure which takes up more space than as a liquid even though there space than as a liquid even though there is still the same amount of matter. is still the same amount of matter.

Ice cubes are less dense than water Ice cubes are less dense than water which makes them float!which makes them float!

This property of water is important to fish This property of water is important to fish and other organisms that live in lakes and and other organisms that live in lakes and ponds that freeze over during the winter.ponds that freeze over during the winter.

Question: Explain what happens to liquid Question: Explain what happens to liquid water as it freezes.water as it freezes.

Water has an unusually high specific heat.Water has an unusually high specific heat. Specific heat=the amount of heat needed to increase the Specific heat=the amount of heat needed to increase the

temperature of a certain mass of a substance by 1 degreetemperature of a certain mass of a substance by 1 degree Compared to other substances, water requires a lot of heat Compared to other substances, water requires a lot of heat

to increase its temperature. This is due to the many to increase its temperature. This is due to the many attractions among water molecules. attractions among water molecules. Other substances, such as air and rocks, have fewer Other substances, such as air and rocks, have fewer

attractions between their molecules, and their attractions between their molecules, and their temperature increases more quickly when heated the temperature increases more quickly when heated the same amount.same amount.

Effects: land areas located near large bodies of water Effects: land areas located near large bodies of water experience less dramaticexperience less dramatic temperature changes than temperature changes than areas far inland.areas far inland.

Q: Explain why it takes a pot of hot water a long time Q: Explain why it takes a pot of hot water a long time to heat up. to heat up.

QuestionsQuestions

1. What causes water molecules to 1. What causes water molecules to be attracted to one another?be attracted to one another?

2. Why does sugar dissolve well in 2. Why does sugar dissolve well in water?water?

3. Describe what is happening to the 3. Describe what is happening to the water molecules as ice melts.water molecules as ice melts.

4. What unusual fact about ice 4. What unusual fact about ice causes it to float in liquid water?causes it to float in liquid water?