Experimental Design Scientific Method Includes qualitative and quantitative observations, hypotheses, predictions and controlled investigations. Hypothesis Proposed answer or explanation to a scientific question using evidence that has to be testable Theory Well-tested scientific explanation of phenomena supported by evidence that is supported by the scientific community Independent Variable The one factor you change on purpose. Dependent Variable - The factor that is the measured response. Control Factors that you do not change or are held constant.

What is the structure of water? Water is a compound that contains two hydrogen atoms (+) and one oxygen atom (-). Chemical formula is H 2 O. Looks like Mickey Mouse.

Covalent vs. Hydrogen Bonding Covalent Bond Hydrogen Bond

Covalent Bond Hydrogen Bond

Water is a Polar covalent Molecule Covalent bond = sharing of electrons Polar = unequal sharing of electrons Why polar? Oxygen atom pulls on the shared electrons in each hydrogen causing a partial POSITIVE charge on each hydrogen and a partial NEGATIVE charge on the oxygen What is the net charge of a water molecule?

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Covalent Bonding Overview Two Types 1.Polar covalent bond – unequal sharing of electrons Ex: water molecules 2.Nonpolar covalent bonds – equal sharing of electrons Ex: Methane (CH4)

Hydrogen Bonds WEAK bond Slightly positive Hydrogen is attracted to a slightly negative charge atom *Think of magnets* H-bonds form and break easily H-bonding allows water molecules to bind to other polar molecules

Is Water Polar or Nonpolar? Answer: Water is a polar molecule, because it contains a positive and negative charge. Examples: - Polar molecule mix with polar molecule. (saltwater) - Polar and nonpolar do not mix. (oil and water) - Nonpolar mix with nonpolar. (milk and chocolate syrup)

Properties of Water 1. Universal Solvent 2. Adhesion 3. Cohesion 4. Capillary Action 5. Surface Tension 6. Density/Buoyancy 7. High Specific Heat

How is water a universal solvent? Definition: Water’s unique property to dissolve most substances (solutes).

Solution is made up of two parts… Solute – Substance that is dissolved Solvent – Does the dissolving Example: Ice Tea: water = solvent; Tea and Sugar = solutes Solution, Solute, & Solvent + =

Real-World Examples: - Salt and water - Instant pancake mix - Kool-aid - Alka-seltzer Question How would our lives be different if water could not dissolve most substances? Water as a Universal Solvent

Why does a suction cup stick better when you put water on it? Suction cups use water’s property of adhesion Adhesion = water to sticks to other substances Real-World Examples: - Suction cup on a window - Rain on a rain jacket - Rain drops on your car windshield

Water’s property of cohesion allows water to bubble on top of the penny Cohesion = water molecule H-bonds to another water molecule Water molecules are very attracted to each other How can a penny hold drops of water?

Capillary Action What will happen when the straw is lowered into water?

Capillary Action How does water move a straw? Because of both Adhesion + Cohesion When adhesion and cohesion work together = capillary action *Think water in a straw*

How do plant roots get their water from the soil? Plants roots rely on water’s property of capillary action Capillary Action = the process that moves water through a narrow porous space. Real-World Example - How all plants get their water

Capillary Action in Organisms Capillary action allows roots to absorb H 2 O from soil Transpiration (evaporation from leaves) H2OH2O H2OH2O

When entering a swimming pool your body is breaking the water’s surface tension Surface Tension = t he force that acts on the particles in water that allow it to become tight Why do belly flops hurt?

Turn and Talk Topic: What property of water allows ice to float? How would our world be different without this property?

How do cruise ships float if they are so big? Upward force of buoyancy & density. - Density = is the mass to volume ratio - Buoyancy = the ability of a water to exert an upward force on an object that is immersed Density of water is 1.0 g/ml

Water has a high heat capacity. “ The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. ” High Heat Capacity

High Specific Heat Properties of Water High specific heat H 2 O acts as a heat reservoir and its temperature remains relatively stable Helps reduce temperature fluctuation in plants and animals High heat of vaporization It takes a lot of heat to evaporate just a little H 2 O This keeps water in lakes and ponds in the summer High heat of fusion It takes much longer for lakes and streams to freeze in winter

Evaporative Cooling During evaporation (liquid  gas), surface temperature of water decreases Mammals sweat to stay cool in high temps

1. Universal Solvent 2. Adhesion 3. Cohesion 4. Capillary Action 5. Surface Tension 6. Density/Buoyancy 7. High specific heat Properties of Water