September 6-October 18 Unit 1: The Hydrosphere

We will introduce our Hydrosphere (water) unit by talking about the properties of water, and make some initial observations about our outdoor habitat I will understand what to expect in our water unit and when taking notes and engage with the environment around me Soap is a…lipid!

The AMAZING Properties of Water

Water is a very COHESIVE substance COhesion = attraction between particles of the same substance Results in Surface Tension (measure of the strength of the water’s surface) Co means 2 Produces a surface film on the water that allows insects to walk across the surface

Water Strider Insect http://www.youtube.com/watch?v=RphuMEUY3Og Ask them first – how do you think they do this? Cohesion produces a surface film on the water that allows insects to walk across the surface Anatomical adaptations and uses the surface tension of water! Why can’t humans do this?

So why does water have such strong cohesion?

Water Structure A water molecule is made up of three atoms: 2 Hydrogen and 1 Oxygen H O

Hydrogen Bonding between Polar Water Molecules  Cohesion Formed between the oxygen atom of one water molecule and the hydrogen atom of another…opposite partial charges attract One hydrogen bond is weak but many are strong.

Similar to Cohesion, is Adhesion Adhesion = Attraction between two different substances Water will make hydrogen bonds with other surfaces (e.g., glass, cotton) What concept from our lab demonstrated this? Capillary action, paper towel (have they done this???). Graduated cylinder and its meniscus!

Capillary Action Capillary action: adhesion and cohesion enable water molecules to move upward through narrow tubes against the force of gravity

Density of Water What is density? Density = mass per unit volume. What do we think if as more/less dense? Does ice float or sink in water? So is it more or less dense? All goes back to the arrangement of hydrogen bonds…

Water as a “Solvent” = ? + Solute, Solvent, Solution What happens when we put table salt (NaCl) into water? + = ? NaCl = the solute (what is being dissolved) Water = solvent (substance into which the solute dissolves)

Make a prediction: How do you think water molecules arrange themselves around Na+? Around Cl- ? https://www.youtube.com/watch?v=EBfGcTAJF4o Based on what you know about water’s polarity.

Are any bonds being broken in this process? Are any bonds being formed? In our bodies: we need Na+ and Cl- in separate form in order for our nerves to work!

Types of Mixtures Homogenous Heterogeneous

Suspension Examples: Sand + Water Oil + Vinegar

Water has a High Specific Heat Specific Heat = amount of heat required to raise 1 gram of a substance by 1˚C Why is the specific heat of water so high? Will the temperature of a lake rise quickly in the summer? Why would water have a high specific heat? When water is heated, most of the thermal energy that water absorbs breaks the hydrogen bonds between the molecules…only after these bonds have been broken does the thermal energy increase the motion of the molecules and raise the temperature of the water Around water, takes longer for temperature to change! Periods 2 and 4 stopped here!

Water has a High Heat of Vaporization Related to Specific Heat What does this mean? A lot of energy is required to turn water into a vapor. Why is this important? Water evaporates slowly and small amounts of water will not routinely dry up.

Water has a Neutral pH pH = relative concentration of hydronium (H30+) ions pH (of water) is neutral (value = 7) when the number of hydronium ions equals the number of hydroxide ions Log scale for pH Dissociation of water: due to strength of attractive forces

Acids and Bases Acids: pH range = 0-7 Bases: pH range = 7-14 Examples = HCl (hydrochloric) and HCH3COO (acetic) Related to H+ concentration (from H30+) Bases: pH range = 7-14 Examples = NaOH or NH3 (Ammonia) pH scale is logarithmic – every step is a power of 10 Noun = acid, Adjective = acidic “Sour taste” Common elements; acetic acid = vinegar! Focus on the H and OH as identifying components!

What is the pH range of Biological Molecules? Enzymes can only function within a certain pH range Buffers = chemical substances that neutralize small amounts of either an acid or base added to a solution More about enzymes later… How do we keep the pH range in our bodies constant?

Properties of Water Jigsaw Cohesion Adhesion Water as a Solvent Water’s High Specific Heat Water’s Neutral pH Your challenge: come up with an everyday example of each property that we did not go over in class! Time dependent, may be for homework. In groups of 5-6, students will explain the property of water in their own words. They will then find a resource online that represents an example of this property! Jigsaw and share out. ***Pass out AFTER notes…

Outdoor Habitat – Initial Observations Four corners (facing center), from stream If mobile, observe it several times on an interval Guidelines Be generous with details If you can’t today, think about how you might take quantitative data Use Mr. Koons for reference info, if you need it! What are things you could look for in our interval observations?