buffer
Post on 24-Oct-2014
243 Views
Preview:
TRANSCRIPT
PELEKEKAE
TUMO LERANG SENWELO
201000004
BIO 211: CELL BOLOGY
EXERCISE 4: BUFFERS IN BIOLOGY
07/09/2011
INTRODUCTION
All living organisms are made up of living units called cells. The cells contain a structure called
the nucleus which is a site for chemical reactions. Chemical reactions are affected by
concentration, pressure and pH so the body needs to make sure that they are in the right amount
to maintain a constant internal environment (Stevens, 2008). One way to minimize pH changes
in a chemical solution is to add a buffer. A buffer in Jones & Atkins (2000) is defined as a
mixture of weak conjugate acids and bases that stabilizes the pH of a solution by both accepting
and providing protons for reaction with added acid or base. The Henderson-Hanselbach equation,
also called the buffer equation is:
pH= pKa+ log [conjugate base]
[Acid]
Buffer work best at controlling pH at pH values roughly equal to the pKa of the component
acid or base i.e. the [salt] is equal to the [ acid] (Cairns, 2000).
The aim of this experiment is to find to distinguish between extracellular and intracellular
buffers, to find out if there are natural buffers in higher animals and also to find out their
effectiveness in controlling hydrogen ion fluctuations.
METHODOLOGY
The groups were merged such that when others titrated with a base (NaOH) others titrated with
an acid (HCl) in order to cover all the solutions provided in three hours. Our group titrated with
HCl while the other titrated with NaOH.
Two solutions were provided; succinic acid (solution 1) and glycine (solution 2) working with
50ml of a 0.1M concentration. Measured out 25ml volume of succinic acid and poured it into a
conical flask provided. Read the pH of the succinic acid in the conical flask and titrated this
solution with hydrochloric acid (HCI). Small volumes of about 0.5ml were added at a time,
swirled the contents of the beaker before recording the pH, the volume added and the pH was
recorded after each addition. The titration was carried until the pH reached 2. The procedure
was repeated as above but in this case succinic acid was replaced with glycine.
The results from the titration with NaOH were collected from the other group that we had
merged with.
The results from this experiment were used to plot a graph and were analyzed.
RESULTS
The plotted graphs are in the next pages
From the graph on the titration of succinic acid with hydrochloric acid (HCl) it can be seen that it
requires less HCl for the pH to drop to 2 than it is required for glysin as the former needed only
10.02ml of HCl while the latter needed 32.98ml of HCl.
However it should be noted that when HCl was replaced with Sodium hydroxide the solutions
required even greater volumes to be added to raise the pH to 12. Because the NaOH is a base it
raises the pH of succinic acid and glysin, the graphs are upward sloping to indicate an increase in
pH whereas with HCl the graphs are downward slopping because the pH is being decreased.
DISCUSSION
With increasing amounts of added base, the overall slope of a graph of pH is downward but
without a buffer, the slope is steep. Inside the buffering range of an added buffer, the slope is
shallow. At very high and very low values of pH, where the buffer is ineffective, hence the
slopes are much steeper. Even when more NaOH was added to the solutions as it can be seen
from the graph, the pH changed slightly and this is in agreement with Sadava (2009) when he
says in the presence of a buffer, additions of even large quantities of base result in relatively
small changes in pH.
There are intra cellular and extra cellular buffers in the body. Intra cellular are buffers that are
inside/ in the interior of the cell while extra cellular refers to buffers outside of the cell. There are
different natural buffers, that can either be intra cellular or extra cellular found in higher animals.
Proteins, organic phosphates, inorganic phosphates (not natural) and in the erythrocytes,
haemoglobin (Cairns, 2000) are intracellular buffers. He goes on to say haemoglobin is the most
excellent because of its ability to bind to hydrogen ions forming a weak acid and carbon dioxide.
Extra cellular buffers include bicarbonate and ammonia and the bicarbonate is especially key as
carbon dioxide can be shifted though carbonic acid to H+ ions and bicarbonate.
Sadava (2009) goes on also to say that the major buffers in the blood are bicarbonate ions
(HCO3) that are formed from the dissociation of carbonic acid, which in turn is formed by the
hydration of CO2 according to the following equilibrium reaction:
CO2+ H2O ←→ H2CO3 ←→ H+ + HCO3-
If excess hydrogen ions are added to this reaction mixture, the reaction moves to the left and
absorbs the excess H+. If hydrogen ions are removed from the reaction mixture, however the
reaction will move to the right and supply more H+.
CONCLUSION
Most buffer systems in the body consist of a weak acid and the salt of that acid, which functions
as a weak base. Buffers prevent rapid drastic changes in the pH of body fluids by converting
strong acids and bases into weak acids and bases within fractions of a second (Tortora G J,
2009). The kidney is one of the organs that is involved in acid-base balance (Bulger, 1983)
In all multicellular organisms, the fluid within the cell and the fluids surrounding the cells have a
characteristic and nearly constant pH which can be maintained through buffer systems. There are
many buffers in higher animals but the principal of the body fluids are the protein buffer system,
the dihydrogen phosphate buffer system and the carbonic acid buffer systems. The phosphate
buffer system operates in the internal fluid of all cells which means that they are intra cellular
while the latter (carbonic acid systems) are extra cellular. Another most important buffer system
is found in the blood plasma because blood pH is a critical variable because it influences the
structure, and therefore the function, of proteins. In mammals, cellular fluid has a pH range 6.9
to 7.21 and the phosphate buffer is effective in maintaining this pH range
REFERENCES
D, C. (2000). Essentials of Pharmaceutical Chemistry. Chicago: Pharmaceutical Press.
E, B. R. (1983). The Urinary System. In W. L, Histology: Cell and Tissue Biology (pp. 867-912).
New York: Elsevier Science Publishing Co.,Inc.
Jones L, A. P. (2000). Chemistry: Molecules,Matter and Change. New York: W. H. Freeman and
Company.
Sadava D, H. D. (2009). Life: The Science of Biology. Sunderland, MA: Sinauer Associates Inc.
Stevens A, L. J. (2008). Human Histology. Philadelphia: Elsievier.
Tortora G J, D. B. (2009). Principles of Anatomy and Physiology. Hoboken: John Wiley &
Sons . Inc.
top related