Why are we spending so much money going to Mars?

Gusev Crater on Mars (taken by the Mars Exploration Rover Spirit on Jan. 10, 2004

Solid

Liquid

Gas

The Amazing Water Molecule

Water covers 75% of the Earth’s Surface and makes up 45%-95% of living organisms

Water is polar.

Hydrogen bonds form betweenwater molecules.

-

+ +

+-

H H

O

Water is both cohesive (sticks to itself) and adhesive (sticks to other types of molecules)

Figure 3.3 Walking on water

In ice, water molecules form a crystal lattice.

In liquid water, no lattice forms, so liquid water is denser than ice.

As a result, ice floats.

Figure 3.5 The structure of ice (Layer 2)

Ice floats and frozen benzene sinks

Liquid

Gas

Molecules have thermal energy

Thermal energy = the kinetic energy of molecular motion

• Temperature = a measure of how much thermal energy the average molecule of an object possesses

• Heat = the total amount of thermal energy that an object has: can be transferred from warmer to cooler objects

Heat vs. Temperature

The Pacific Ocean has a low temperature, but a lot of heat

Ice water steam

Water has high specific heat = the amount of energy required to raise the temperature of 1 gram of substance 1° Celsius

Areas near large bodies of water have a fairly stable temperature

Evaporative cooling

Water has a high Heat of Vaporization: the amount of heat that must be transferred to a

liquid to change it from liquid to gas

Water as a solvent

Since water is polar, the positive and negative

ends of a water molecule will be attracted to

charged ions or other polar molecules

Solvent

Solute

Solution

Like dissolves Like

Hydrophilic: ionic or polar substances that have an affinity for water

Hydrophobic: non-ionic or nonpolar substances that do not have an affinity for water

Chemical reaction: hydrogen bond shift

€

H2O ⇔ H++OH−

OR

Acids, Bases, and the pH scale

Acids = substances that release H+ ions (increasing H+ concentration)

• HCl H+ + Cl-

Bases = substances that release OH- ions or accept H+ ions (decreasing H+ concentration)

• NaOH Na+ + OH-

• NH3 + H+ NH4

Figure 3.9 The pH of some aqueous solutions

pH = -log[H+]

Example: Water[H+] = 10-7 M

So the pH is-log(10-7) = -(-7) = 7

Buffers are substances that help maintain a constant pH in a solution

Example: Carbonic acid

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H2CO3rising pH ⏐ → ⏐ ⏐ HCO3

-+H+

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lower pH← ⏐ ⏐ ⏐