Transcript H + + HCO 3

Chemical Reactions
In a chemical reaction, the reactant(s) is (are) what
you start with, while the product(s) is (are) what
you end up with.
A + B ------> A-B
reactants
product
A-B ------> A + B
reactants
product
The chemical bonds that hold atoms and ions
together contain potential or stored energy.
This means that when chemical bonds are formed,
energy is required, and when chemical bonds are
broken, energy is released.
Forming a chemical bond: energy in
Energy
A + B ------> A-B
• requires energy
• small molecules ---> larger molecules
• synthesis reaction
• anabolic reaction
Ex:
amino acids ---> proteins
Breaking a chemical bond: energy out
Energy
A-B ----> A + B
• releases energy
• larger molecules ---> smaller molecules
• decomposition reaction
• catabolic reaction
Ex:
protein -----> amino acids
Classification of chemicals in living systems:
Inorganic
Organic
• usually not contain C
• usually contain C
• use ionic and some
covalent bonding
• use covalent bonding
• relatively small
• relatively large
• many dissolve in
water to release ions
• most not readily soluble
in water; do not release
ions
• ex: acids
bases, salts
• ex: proteins, sugars,
fats
Inorganic chemicals
Acids:
chemicals that dissociate in water to
release one or more hydrogen ions (H+)
and one or more anions.
HCl
H+ + Clstrong acid
Strong acids tend to dissociate or ionize completely to
produce large numbers of H+. This is indicated by the
arrow which runs in only one direction.
Here is a second example of an acid, carbonic acid.
This acid is described as a weak acid since it does not
completely dissociate (arrows going in two directions.)
H2CO3
H+ + HCO3-
carbonic acid
weak acid
bicarbonate
ion
It is “weak” since it produces fewer H+ in solution
than an acid that dissociates completely.
We will look at two definitions of bases.
Bases:
1) chemicals that dissociate in water
to release hydroxide ions (OH-) and
one or more cations.
NaOH
Na+ + OH-
This is an example of a strong base.
Bases: 2) chemicals that remove (H+) from solution
Looking again at NaOH:
NaOH
Na+ + OH-
When OH- are released into a solution they have a
tendency combine with any available H+ and to
remove them from solution
OH- + H+
H- OH (= H2O)
Summary:
acids – chemicals that add H+ to a
solution
bases – chemicals that remove H+ from
a solution
Salts:
chemicals that dissociate in water to
release a cation other than H+ and
anion other than OH-
NaCl ----> Na+ + Cl-
In biology, when measuring the acidity or alkalinity of
solutions one uses a special scale called the pH scale.
The pH scale describes the concentration of H+
present in a solution.
pH scale runs 0 - 14
0 - 6.9 = acidic range
7.0 = neutral
7.1 - 14 = basic range
decreasing concentration H+
less acidic
0………….7………….14
more acidic
increasing concentration H+
Although the pH scale only runs from 0 to 14, a
single unit change on the pH scale = 10X change in
H+ concentration.
example: pH 4.0
pH 3.0
concentration H+ increases 10 X
example: pH 4.0
pH 2.0
concentration H+ increases 100 X
In the same way, as one goes up the pH scale, and
acidity decreases, a single unit change on pH scale
reflects a 1/10 reduction in H+ concentration.
example: pH 6.0
pH 7.0
concentration H+ at 7.0 is 1/10 that at 6.0
example: pH 6.0
pH 8.0
concentration H+ at 8.0 is 1/100 that at 6.0
In order to maintain pH homeostasis, biological systems
often depend on chemical buffering systems.
buffer : chemicals or system of chemicals that
resist changes in pH
In order to maintain a relatively steady pH, a
good buffering system must be able to do two
things:
• remove H+ from a solution when there are
too many H+
and
• release H+ into solution when there are
too few H+
Example of a buffer system:
combination of
H+ + HCO3-
H2CO3
carbonic acid
and
bicarbonate ion
If pH drops due to increasing numbers of H+
H+ + HCO3-
H2CO3
the bicarbonate ion begins to pick up the
extra H+ from solution to form carbonic acid.
Removing the H+ from solution keep them
from lowering pH.
On the other hand, when pH rises due to the
loss or removal of H+
H+
+ HCO3-
H2CO3
the carbonic acid begins to dissociate to add
H+ to the solution.
Adding H+ to the solution will prevent the pH
from rising.
In this way, the buffer is able to handle both increases
and decreases in H+ and maintain a steady pH.
H2CO3
carbonic acid
H+ + HCO3bicarbonate ion