Case 4: Too much or too little? BBS1001 2023/2024
15 september 2023
PBS phosphate buffered saline prevents cells rupturing or shriveling up due to
osmosis.
Keywords
- Blood sample
- PBS
- Activity of enzymes in blood
- Target enzymes
- Interactions with enzymes
- pH and pKA
- Control sample
- Acid and base
- Chemical buffers
-
Problem statement
Controlling of body pH
Learning goals
1. What is acidity/ alkalinity / pH.
2. How pH works.
3. Types of acids and bases + differences
4. What are buffers + important buffers system.
5. How buffers regulate solutions.
6. Different types of solution + what is osmolality and why is it important.
7. What is the Henderson-Hasselbalch equation? How to use it?
, Case 4: Too much or too little?
1. What is acidity(acid)/ alkalinity (base) / pH.
Acidity and alkalinity
There are two main theories of acidity and alkalinity: the Brønsted-Lowry theory and the
Lewis theory.
The Brønsted-Lowry theory defines an acid as a proton (H+) donor, and therefore, alkalines
are proton acceptors. This is the most useful current theory of acids and bases. For a
compound to be able to act as a Brønsted-Lowry acid, it must have a hydrogen atom which
it can lose but still remain somewhat stable. Some compounds can act as both acids and
bases – such as water because it can either lose a hydrogen atom to form OH - or gain one to
form H3O+. These compounds are called amphiprotic.
The Lewis theory is a little more complicated and focuses on electron pairs. It defines an
acid as an electron pair acceptor, and therefore, alkalines are electron pair donors. This
definition is much broader than the Brønsted-Lowry theory because it includes compounds
that, whilst they do not have protons, they still show acid/base behavior.
One important thing to remember is that, on the pH scale, the smaller the pH, the greater
the concentration of protons.
pH
The pH of a solution is a measure of its acidity or alkalinity. The range goes from 0 – 14, with
7 being neutral. pH’s of less than 7 indicate acidity, whereas a pH of greater than 7 indicates
a base. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in
the water. Solutions that have more hydrogen ions (H+) is acidic, whereas solutions that
have more hydroxide ions (OH-) is basic (alkaline). Since pH can be affected by chemical in
the water, pH is an important indicator of water that is changing chemically. pH is reported
in ‘logarithmic units.’ Each number represents a 10-fold change in the acidity/basicness of
the water. Water with a pH of five is ten times more acidic than water having a pH of six.
The blood in our veins is slightly alkaline (pH= 7,4). The environment in our stomach is highly
acidic (pH= 1 to 2).
pH + pOH = 14,00
Ka = [H+] [A-] / [HA]
2. How pH works.
The equation for calculating pH pH = -log[H+] or pH = -log[H3O+].
Where log is the base-10 logarithm and [H+] stands for the hydrogen ion concentration in
units of moles per liter solution.
Rough pH measurements can be made using litmus paper or another type of pH paper
known to change colors around a certain pH value. Most indicators and pH papers are useful
only to tell whether a substance is an acid or a base or to identify pH within a narrow range.
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