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.

Water’s Unique Properties

What is the structure of water?Water is a compound that contains

two hydrogen atoms (+) and one oxygen atom (-).

Chemical formula is H2O.Looks like Mickey Mouse.

Covalent vs. Hydrogen Bonding

Covalent Bond

Hydrogen Bond

Covalent Bond Hydrogen Bond

Water is a Polar covalent MoleculeCovalent bond = sharing of electronsPolar = 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?

Please sit quietly and wait for instructions.

Please get out your interactive notebooks .

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 BondsWEAK bond

Slightly positive Hydrogen is attracted to a slightly negative charge atom

*Think of magnets*

H-bonds form and break easilyH-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.Adhesion3.Cohesion4.Capillary Action 5.Surface Tension6.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

QuestionHow 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

adhesionAdhesion = 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 25-30 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 actionCapillary 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 H2O from soil

Transpiration (evaporation from leaves)

H2O

H2O

When entering a swimming pool your body is breaking the water’s surface tension

Surface Tension = the 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 HeatProperties of WaterHigh specific heat

H2O 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 H2OThis 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 Evaporative Cooling

During evaporation (liquid gas), surface temperature of water decreases

Mammals sweat to stay cool in high temps

1. Universal Solvent 2. Adhesion3. Cohesion4. Capillary Action 5. Surface Tension6. Density/Buoyancy 7. High specific heat

Properties of Water