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
€
H2CO3rising pH ⏐ → ⏐ ⏐ HCO3
-+H+
€
lower pH← ⏐ ⏐ ⏐
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