Transcript Water Properties & pH

Biology I
Water
 About 60-90 percent of an
organism is composed of
water
Water is
used in most
reactions in the body
 Water
is called the
universal solvent
 Water
is the single
most abundant
compound in living
thing
Question:
• What are the three
states of water?
• Answer:
• 1.ice
2.liquid
3.water vapor (gas)
The
States
of
Water
GAS
LIQUID
SOLID
Water Properties
Polarity
Cohesiveness
Adhesiveness
Surface
Tension
Polarity of Water
Water is a “polar” molecule, meaning that there is
an uneven distribution of electrons.
Water has a partial negative charge near the
oxygen atom due to the unshared pairs of
electrons, and partial positive charges near the
hydrogen atoms.
This causes them to stick like small magnets,
making a hydrogen bond (weakest bonds, easy to
break & easily formed again)
Water (H2O)
Cohesion & Adhesion
1. Hydrogen bonds (H-bonds) cause water
molecules to stick together.
2. Aides in the transport of water from roots to
the leaves.
3. Water is attracted to other water, this is called cohesion.
4. Water can also be attracted to other materials. This is
called adhesion.
The oxygen end of water has a negative charge and the hydrogen end has a
positive charge. The hydrogen of one water molecule are attracted to the
oxygen from other water molecules. This attractive force is what gives
water its cohesive and adhesive properties.
Surface tension
Surface tension
1. Related to cohesion
(H-bonds)
2. Allow water striders
(insects) to walk on water.
Surface tension is the name we
give to the cohesion of water
molecules at the surface of a
body of water.
Capillary Action
• Surface tension is related to the
cohesive properties of water. Capillary
action however, is related to the
adhesive properties of water. You can
see capillary action 'in action' by
placing a straw into a glass of water.
The water 'climbs' up the straw. What is
happening is that the water molecules
are attracted to the straw molecules.
When one water molecule moves closer
to a the straw molecules the other water
molecules (which are cohesively
attracted to that water molecule) also
move up into the straw.
Water (H2O) & Solutions
Water is known as the universal solvent
Water dissolves an enormous variety of solutes.
solvent (water) + solute (salt)  solution
Not all things are pure substances. Some are
mixtures that contain more than one substance.
Solutions are mixtures in which one or more
substances are evenly distributed in another
substance
Water (H2O)
• Remember:
1. Water is a good solvent and is
hydrophilic (water loving) for other
polar molecules and ions.
2. Hydrophobic (water hating)
interactions occur between water and
non-polar molecules like fat (lipids).
Solutions & Suspensions
• Solute-substance being dissolved in the solution
• Solvent-substance in which solute is being dissolved
• Aqueous solution-solution in which water is the
solvent
• Suspensions-mixtures of non-dissolved material and
water
Acids & Bases
• The degree of acidity or alkalinity (basic) is
important in organisms
• The force of attraction between molecules is so strong
that the oxygen atom of one molecule can actually
remove the hydrogen from other water molecules;
called Dissociation
• H20-----GOES TO----- H+ + OH• OH- called hydroxide ion; H+ called hydrogen ion
Acids & Bases Cont…
• Acidity or alkalinity is a measure of the
relative amount of H+ and OH- ions
dissolved in a solution
• Neutral solutions have an equal number of
H+ and OH- ions
• Acids have more H3O+ ions than OH- ions;
taste sour; and can be corrosive
• Bases contain more OH- ions than H3O+
ions; taste bitter; & feel slippery
Acids and Bases
• One of the most important aspects of a living
system is the degree of acidity or alkalinity
Acids
• Number of hydronium ions in solutions is
greater than the number of hydroxide ions
• HCl  H+ + Cl-
Bases
• Number of hydroxide ions in solution is
greater than the number of hydronium ions
• NaOH  Na+ + OH-
Examples of Common
Acids
•citric acid (from certain
fruits and veggies,
notably citrus fruits)
•ascorbic acid (vitamin C,
as from certain fruits)
•vinegar (5% acetic acid)
•carbonic acid (for
carbonation of soft
drinks)
•lactic acid (in
buttermilk)
Examples of Common
Bases
•detergents
•soap
•lye (NaOH)
•household ammonia
pH Scale
• Compares the relative
concentration of H3O+
ions and OH- ions
• Scale ranges from 0 to 14;
0-3 is very acidic; 7 is
neutral; 11-14 is very
basic or alkaline
• Litmus paper,
phenolphthalein, pH paper,
& other indicators that
change color can be used to
measure pH
pH Cont…..
• Using litmus paper:
An acid turns blue
litmus paper red and a
base turns red litmus
paper blue.
pH Scale
• Scale for
comparing the
relative
concentrations
of hydronium
ions and
hydroxide ions
in a solution
• Scale ranges
from 0 to 14
• The lower the pH the stronger the acid
• The higher the pH the stronger the base
• pH 7.0 is neutral
Acids
• Proton donor
• High number of H+ - protons and low # of OH• Examples:
HCl (hydrochloric acid)
H2SO4 (sulfuric acid)- ACID
RAIN
H+H+H+H+H+
H+H+H+H+H+
H+H+H+H+H+
OH- OH-
Base
• Proton acceptor
• Low number of H+ and high # of OH• Examples:
NaOH (sodium hydroxide)
NH3 (ammonia)
OH-OH- OHOH-OH-OHOH-OH-OHOH-OH-OHH+H+
Neutral Solution
•
•
•
•
pH of 7 is neither acidic or basic.
It is said to be neutral.
This means that there are as many H+ as OH-.
Pure water and blood are neutral.
H+ H+ H+
OH-OH-OHOH-OH-OHH+H+ H+
Buffers
• Control of pH is
important to
organisms
• Enzymes function
only within a narrow
pH range; usually
neutral
• Buffers neutral acids
or bases in organisms
to help control pH