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Acid-Base
LO1 - Define the terms acid, base, pH, acidosis and alkalosis
Acids and bases
• Acids and bases are electrolytes - they ionise and dissociate in water and conduct as an
electrical current
• Acids
- Have a sour taste, can dissolve metals
- A substance that releases hydrogen ions, H+, a proton donor
- An acid in water releases a proton and an anion
- The concentration of protons determines the acidity of a solution
- Anions have little or no effect on acidity
- Acids in the body are hydrochloric acid, HCl, acetic acid, HC2H3O2, and carbonic
acid, H2CO3
• Bases
- Have a bitter taste and feel slippery
- Takes up hydrogen ions, is a proton acceptor
- Inorganic bases include hydroxides, which dissociate in water, but hydroxyl ions, OH-,
are liberated
- After dissociation the hydroxyl ion binds to a hydrogen ion, creating water
- Bicarbonate ion, HCO3-, is an important base in the body and is abundant in the
blood
- Ammonia, NH3, is a common waste product of protein breakdown, which has a pair of
unshared electrons that strongly attracts protons
• pH: acid-base concentration
- The more hydrogen ions in a solution, the more acidic the solution is, and the lower
the pH
- The more hydroxyl ions in a solution, the more basic, and the higher the pH
- pH scale is from 0 to 14 and is logarithmic, meaning it is defined as the negative
logarithm of the hydrogen ion concentration
- At a pH of 7 a solution is neutral, a pH of below 7 is acidic, and above 7 is basic
• Neutralisation
- Occurs when an acid and base are mixed together
- The joining of the H+ of the acid and the OH- of the base create water, neutralising
the solution
- A reaction is written with the salt together, but it is still dissociated in the solution
• Buffers
- Living cells are extremely sensitive to slight changes in pH
- Homeostasis of pH is regulated by the kidneys and lungs and by chemical systems,
buffers
- Buffers act as acids when pH rises by releasing H+, and as acids when pH drops by
binding H+ ions
- If pH varies from a pH of 7.35 to 7.45, it can possibly be fatal
- Strong acids and bases dissociate completely in water altering pH a lot, whereas
weak acids and bases only partially dissociate and hence only altering pH a little
- Chemical equilibrium between carbonic acid, a weak acid, and a bicarbonate ion, a
weak base, resists changes in blood pH by shifting to the right or left of the equation
as H+ ions are taken or added to the blood
• As pH rises, the equilibrium shifts to the right which forces more carbonic acid to
dissociate
• As pH drops, the equilibrium shifts to the left as bicarbonate ions begin to bind with
protons
• Strong bases are replaced by a weak acids, and protons released by strong acids
are tied up in a weak one
LO2 - Describe the 3 ways in which plasma pH is regulated: chemical
buffer system, the lungs (respiratory system) and the kidneys (changes in
excretion of acid)
All functional proteins are influenced by H+ concentration due to their abundant hydrogen
bonds
The acid-base balance of the body is closely regulated as nearly all biochemical reactions
are influenced by the pH of surrounding fluids
Optimal pH varies from one body fluid to another - pH is lower in cells and venous blood
reflects their greater amounts of acidic metabolites and carbon dioxide, which when
combined form carbonic acid
When the pH of arterial blood is above 7.45 alkalosis is diagnosed, and when it is below
7.35 acidosis or academy is diagnosed
pH between 7 and 7.35 isn't technically acidic, so it is referred to as physiological acidosis
Small amounts of acidic substances enter the body through the food that we eat, with most
hydrogen ions originate as metabolic by products or end products
H+ concentration is regulated by chemical buffers, brain stem respiratory centres, and
renal mechanisms
Chemical buffers act within a few seconds, respiratory changes including rate and depth
occur within 1 to 3 minutes to deal with alkalosis and acidosis, and the kidneys requires
hours or even over a day to alter blood pH
Chemical buffer systems
• Weak acids, although they don't dissociate fully, are efficient at preventing pH changes