Journal Question

If you have ever seen a photograph of Earth from space, you know that much of the planet is covered by water. Water makes life on Earth possible. If life as we know it exists on some other planet, water must be present to support that life.

a.) Try to make a list of 10 things that have water in them

b.) Compare your list to another student and add to your list

c.) Did either list contain any living things?

Properties of WaterBiology - Irwin

Why is Water So Important??

The Water Molecule – H2O

In your journal, draw the hydrogen and oxygen atom like we have done earlier in the unit (Bohr Model)

How many protons (+) are in the nucleus of an oxygen atom?

How many protons (+) are in the nucleus of a hydrogen atom?

Does the nucleus of the oxygen atom or the hydrogen atom attract electrons more strongly?

Water molecules are polar

Polar because of an uneven distribution of electrons between the oxygen and hydrogen atoms

A water molecule has both partial negative charges and partial positive charges.

O

HH

(-)

(+) (+)

Journal Question

Think of the interaction of two magnets and how they either are attracted to each other or repel. Then draw a picture of how you think the water molecules will interact with each other.

Hydrogen Bonding

Polar water molecules can attract each other.

Hydrogen atom with partial positive charge (+) is attracted to the partial negative charge (-) of another atom (oxygen) This is known as a hydrogen bond

Not as strong as covalent or ionic bonds

Bonding between molecules

Activity #1 – Penny Wars

For this mini lab you will need: Penny Paper towel Small beaker (cup) of water Dropper

Each student will write down their prediction for how many drops of water that can be held on the penny (heads or tails) until the water spills over onto the paper towel.

Properties of Water

Cohesion

Cohesion

Attraction between molecules of the same substance (water)

Water molecules can form up to four hydrogen bonds at the same time so it is very cohesive.

Examples: Beads of water on leaves Raft spider Surface tension – glass of milk that is poured to

very top and somehow doesn’t spill.

Activity #2

Part 1: For this mini lab, you will add water to the Petri dish from a small beaker. Use your fingers to “float” the small paper clip on the surface of the water. Record your observations

Part 2: Add two drops of soapy water with a dropper to your Petri dish Record your observations

Follow-Up Lab Questions

Penny Wars: How many drops of water could your penny hold before it spilled over onto the paper towel?

Penny Wars: What property of water made it possible for so many drops of water to stay on the penny? Explain!

Soap and Paper Clips: How did the paper clip “float” on top of the water?

Soap and Paper Clips: Why did the paper clip sink once the soap was added to the Petri dish?

Properties of Water

Adhesion

Activity #3 – Water in Graduated Cylinders

In your group, add water into your glass graduated cylinder until it is about half full. Remember how we discussed earlier in the year that the meniscus is the curvature you see at the the water level line. Draw a sketch of your water in the graduated

cylinder and label the meniscus

Adhesion

Attraction between molecules of different substances

Ex.) Water forms “meniscus” in graduated cylinder Adhesion between water molecules and glass

molecules is stronger than cohesion between water molecules

Activty #4 – Capillary Action in Flowers

We know that plants are mainly made up of water, but how does it get from the soil up to the leaves of the plant?

Capillary Action!

Question:

Think about an extremely hot day in the summer that is followed by a very cold rainy day. Are the fish and other aquatic organisms in Lake Michigan in danger due to very high or low water temperatures?

NO. Water absorbs large amounts of heat with only very small changes in temperature, so aquatic organisms are protected by drastic temperature changes.

High Heat Capacity

Heat Capacity: Amount of heat energy needed to increase waters temperature

Water had a high heat capacity due to the hydrogen bonds between molecules A large amount of heat energy is needed to cause

the molecules to move faster and raise the temperature of water.

Ice

Why does ice float in water?

Why does ice float in water?

Water is less dense as a solid than a liquid Solid water (ice) = less dense Liquid water = more dense Example: Rocks and water

Solid water floats

Mixture

Mixture: Material composed of two or more elements or compounds that are physically mixed together but not chemically combined.

Examples: Salt and pepper mixed together Sugar and sand mixed together

Two types of mixtures: Solutions Suspensions

Solutions

Solution: all components are evenly distributed throughout the solution

Solute: substance that is dissolved

Solvent: substance in which the solute dissolves

Aqueous solutions: Solutions where the solvent is water

Mini Lab

At your table, fill your test tube up about half way with water.

Add a small pinch of salt and gently mix together until dissolved.

Identify the solvent, solute and solution.

Is this an aqueous solution? Why?

How does water dissolve table salt?

Table salt (NaCl)

Remember that NaCl is bonded together by an ionic bond. Write out the two ions with their charges for table salt.

Draw a solid piece of salt at the molecular level.

Draw a water molecule, and add its partial charges. Remember water is POLAR!

How do you think water dissolves table salt?

http://www.4shared.com/video/I9Huy_EY/Dissociation_of_salt.html?cau2=403tNull

Water is the Best Solvent on Earth!

Since water is polar, it can dissolve ionic compounds and other polar molecules

Can dissolve salts, sugars, minerals, and some gases

Mini Lab Part 2

Dump out the water and salt solution and add about 15 mL of water and a large spoon full of salt.

Gently shake the solution until the salt is dissolved

What did you notice?

Saturated solutions: when solvent has dissolved all of the solute possible

Unsaturated: not all of the solute have been dissolved by the solvent

Suspensions

Suspensions: when some materials do not dissolve when placed in water Materials separate into very small pieces so they do

not settle out right away. Water molecules are always moving so they keep

small particles suspended for a period of time

Examples: Blood is a suspension Flour in water is a suspension

Acids and Bases

Water molecules sometimes split apart to form ions.

H2O H+ + OH-

Water hydrogen ion + hydroxide ion

Pure water is neutral # H+ = # OH-

pH Scale

Indicates concentration of H+ ions in a solution

pH Scale

Neutral: pH of 7 Concentration of OH- and H+ are equal

Acids: Compounds that form H+ ions in a solution More H+ than OH-

Bases: Compound that produces hydroxide (OH-) ions in solution Alkaline More OH- than H+

Buffers

Buffers prevent drastic changes in pH

Buffers: weak acids or bases that can react with strong acids or bases to prevent sudden changes in pH