Monday, March 1, 2010

PROPERTIES OF WATER

Chapter 3

Remember: Polar—unequal sharing of electrons (as in an H20 molecules—oxygen is slightly negative, hydrogen is slightly positive)

Surface tension: measure of how difficult it is to stretch or break the surface of a liquid—> hydrogen bonds










http://www.societyofrobots.com/images/robot_JB_lizard1.jpg

The so-called "Jesus Lizard"

Water can moderate temperature because of its high specific heat. Specific heat is the amount of heat required to raise or lower the temperature of a substance by 1 degree Celsius and the specific heat of water is 1 cal/g C (water has very high specific heat, so it takes more heat energy to raise the temperature of water, and more energy must be lost from water before its temperature will decrease).

It would take a huge amount of energy just to bump up the temperature of the ocean 1 degree Celsius. Water has high specific heat for this reason, because otherwise, the critters would die.

Water is also an important solvent. Review: the substance that something is dissolved in is the solvent, while the substance being dissolved is the solute. Together, they are the solution. When the solution has water as its solvent, it’s called an aqueous solution.

Substances that are water-soluble are hydrophilic substances. They are ionic compounds, polar molecules (sugars), and some proteins. Oils, however, are hydrophobic and non-polar, meaning that they do not dissolve in water.

Water is at its densest at 4 degrees Celsius.

The dissociation of water molecules

When a hydrogen atom is transferred from one water molecule to another, it leaves its electron and is transferred as a hydrogen ion, which is a proton with a charge of +1. This transfer makes the water molecule that lost its proton the hydroxide ion (OH-) and the molecule that gains the proton is the hydronium ion, H30+ (lack of it would be a base, more of it would be an acid). This dissociation of water molecules happens such that the amount of hydronium and hydroxide ions is about even in pure water. But if acids or bases are added to water, this equilibrium shifts. Water has a pH of 7, which means it’s neutral.

Buffers: substance that minimizes large sudden changes in pH.

Are combinations of H+ donors and H+ acceptor forms in solution of weak acids or bases.

Work by accepting H+ ions from solution when they are in excess and by donating H+ ions to the solution when they have been depleted.

Eg. Bicarbonate is a buffer.

Chapter 4

Carbon skeleton—Every macromolecule has a carbon skeleton.

Linear

Branch

Ring

4 macromolecules:

1. Lipids

2. Nucleic acids

3. Carbohydrates

4. Proteins

Isomers are compounds with the same molecular formula but with different structures and hence different properties. Isomers are a source of variation among organic molecules.

There are three types of isomers:

Structural, geometric, and enantiomers

Structural isomers are isomers that differ in the covalent arrangement of their atoms

Salem molecular formula, skeleton may change, and can differ in location of double bonds.

Eg. C—C=C instead of C=C—C

Geometric isomers are isomers that share the same covalent partnerships, but differ in their spatial arrangement.

Double bonds are inflexible.

Enantiomers are isomers that are mirror images of each other

Usually one form is biologically active and its mirror image is not.

FUNCTIONAL GROUPS

Hydroxyl Group

-OH and OH+ (the negative out in front is a bond sign, not a negative sign)

Carbonyl group:

Aldehyde—carbonyl is at the end off the carbon skeleton. (A for Away)

Ketone—carbonyl is in the middle or near the end of the carbon skeleton.

Carboxylic Acids:

Since this group donates protons, it has acidic properties.

Amino Group:

Characterized by nitrogen joined to atleast one alkyl group. Tends to act as a weak base.

Sulfhydrol group:

Helps stabilize the structure of protein. Disulfide bridges help stabilize tertiary structure proteins.

Organic compounds with this functional group are called thiols.

Phosphate group:

PO4 3-

Has acidic properties since it loses protons

Organic phosphates are important in cellular energy storage and transfer.

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