Question

Whether you agree or disagree with the concept of global warming, one thing is clear....the oceans are becoming more acidic with time. Although the changes in pH are small in number, it is enough change to have a detremental effect on the coral systems living within the ocean (as remember pH operates on a logarithm). In many real world applications, as with the coral systems in the ocean, small changes in pH can cause death. However, some of these systems have built in buffer mechanisms to maintain pH in cases where it could be deadly in cases of very small changes.

In this week's discussion:

A) Describe the term pH and and the pH scale briefly.

B) Describe the chemistry behind a physiological buffer system.

C) Describe a scenario (other than the oceans and blood) where small changes in pH are critical and whether that described system has a buffer mechanism.

Answer 1

A) pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14. A pH level of 7.0 at 25°C is defined as 'neutral' because the concentration of H₃O⁺ equals the concentration of OH⁻ in pure water, pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.

Very strong acids may have a negative pH, while very strong bases may have a pH greater than 14.

The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6.

The equation for calculating pH was proposed in 1909 by Danish biochemist Søren Peter Lauritz Sørensen:

pH = -log[H⁺]

where log is the base-10 logarithm and [H⁺] stands for the hydrogen ion concentration in units of moles per liter solution.

B) Physiological buffers are chemicals used by the body to prevent large changes in the pH of a bodily fluid which include bicarbonate, phosphate, hemoglobin, and protein systems.

The pH of a buffer is determined by the Henderson-Hasselbalch equation:

pH = pKa+log[A] [HA]

Buffer has the capacity to resist changes in pH when the pH of the buffer is close to the pH of blood (7.37 to 7.42), So the pKa of the acid should be close to 7.4.

Phosphate buffer system consists of H₂PO₄⁻ and HPO₄²⁻ ions.

Carbonate buffer - The enzyme carbonic anhydrase converts H₂CO₃ into CO₂ that is dissolved in the blood and is then exhaled as CO₂ gas.

The general equation for Hemoglobin is:

HHb⁺+ O₂ + H₂O ⇌ HbO₂ + H₃O⁺ ; pKa=6.8

Proteins

A protein is a long chain of amino acid residues, but this long chain still has free carboxylate groups COO⁻ and free amino groups NH₂.

C) Our body works within the pH range of 7.0-7.8. Our system produces HCl which helps in the digestion of food. During indigestion, the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases such as antacids.