Unit 2 BioChemistry
Section 2 Water
Most abundant compound, exists in 3 phases
70% of earth is covered with water & 60% of body is made of water.
H2O : Molecule – more than one atom
Compound – more than one type of element
O has 1 covalent bond with each H
Polarity : Oxygen and hydrogen are held together by a strong covalent bond
O (8 protons) has a stronger electronegativity than H
electrons are shared unequally
the electrons surround oxygen more
makes oxygen side of the molecule partially negative
makes the hydrogen side of the molecule partly positive
Polar molecule is a molecule where charges are unevenly distributed.
Hydrogen Bonds: Weak bond between molecules
(Not between atoms to create a molecule, that’s covalent and ionic)
Hydrogen is often partially positively charged and makes weak bonds with partially
negatively charged Oxygen of other molecules.
H2O molecules sticking together;
H+ area of one atom attracting the O- areas of a different atom.
1 H2O molecule can form hydrogen bonds with 4 other H2O molecules
Draw 5 Water
Polarity of water molecules
molecules here
Allows them to form hydrogen bonds with each other
Contributes to the various properties water exhibits
Properties of Water
Cohesion :
Same type of molecule attracted to each other
Ex: H2O molecules stick together and form droplets
Surface tension:
Due to cohesion surface of water appears & act as membrane (invisible skin)
Ex. Insects walk on water surface.
Adhesion
Different types of molecules attracted to each other
Water molecules stick to other polar molecules
Ex: H2O sticks to the glass forming meniscus
Capillary Action – Cohesion and adhesion lead to capillarity
H2O rises in a narrow tube against gravity.
This is how water gets from the roots of a plant to the leaves.
Water Expands upon freezing and ice is less dense than water
Ice floats on the top
prevents entire pond or lake from freezing
acts as blanket to moderate temperatures below life
allows more organisms to survive winter
High specific heat:
takes a long time to heat up
takes a long time to cool down
(doesn’t transfer heat quickly)
High heat of vaopization
phase change from liquid water to gas (water vapor) requires heat
that heat is pulled from your body as sweat evaporates
Universal solvent
dissolves polar substances by making hydration shell
does not dissolve nonpolar molecules
Mixture : 2 or more substances physically mixed, but NOT chemically combined
(so NOT H2O, H is chemically bonded to the O)
Ex. Earth’s atmosphere is a mixture of gases
1.Solution – Homogeneous mixture (one sub is dissolved in another)
mixture where solute (ex: salt) is dissolved in the solvent (ex: water)
Particles are evenly distributed
H2O is the greatest solvent in the world
2. Suspension -Mixture that is not dissolved but remains suspended
Ex. Sand in water, blood with cells
pH : The concentration of H+ ions
(parts hydrogen or percent hydrogen)
neutral
pH Scale
Acids
1
Bases
7
more H+ions
less OH- ions
14
less H+ ions
more OH- ions
Each step is 10X more or less concentrated than the previous step.
EX:
pH 4 has
pH 3 has
pH 2 has
pH 5 has
pH 6 has
10
_____
_____
_____
_____
H+ ions
H+ ions
H+ ions
H+ ions
H+ ions
Acid is a compound that forms H+ ions in solution
Base is a compound that forms OH- ions in solution
Buffers – weak acids or bases that help maintain homeostasis.
They react with strong acids or bases to prevent sharp sudden changes in pH.