When you added 2 of IN NaOH distilled water what happened to

When you added 2 of IN NaOH distilled water, what happened to the pH? What happened to the proton concentration? when you measured the pH of the buffer alone, how do you account for a reading other than pH 6? what evidence did you get from this exercise to support the definition of a buffer as a chemical that resists changes in pH? Name some biological solutions in which buffers are very important.

Solution

Ans: 3. The pH gets raised when two drops of 1N NaoH is added to the distilled water dut to raise in proton concentration.

Solid NaOH consists of Na⁺ and OH^- ions packed into a crystalline lattice. When this solid is added to water, the ions float apart leading to extra OH^- ions in the water: NaOH OH^- + Na⁺. The resulting large concentration of OH^- makes the solution more basic and leads to a dramatic increase in the pH. (Remember that since the product of concentrations, [OH^-][H⁺], remains fixed at K_w=10^-14, as the concentration of OH^- ions goes up, the concentration of H⁺ ions goes down.)

Ans:4. A buffer solution is a solution that resists changes in pH caused by the addition of acid or alkali. There are two types of buffers: acidic and basic.

Acidic buffers comprise of a weak acid and its salt. eg. ethanoic acid and sodium ethanoate. Basic Buffers comprise of a weak base and its conjugate salt. eg. aqueous ammonia and ammonium chloride.

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications.

Ans 5. solutions with a pH below 7.0 are termed acidic and solutions with a pH above 7.0 are termed basic.

Ans 6.  

1. Bicarbonate buffering system is used to regulate the pH of blood.

2.      Phosphate buffers
3.      Protein buffers

Importance of Buffers in Physiological Systems:

Processes that take place in living organisms are called physiological processes. Like blood circulatory system, respiration etc. The internal pH of most living cells is close to 7.0. The pH of human blood is 7.4. A blood pH of below 7 or above 7.8 can cause death within minutes. So buffering of blood pH is very important to stabilize it around 7.4. pH plays an important role in almost all biological processes. Small change in pH i.e. deceased or high pH can cause metabolic implications in human body like acidosis and alkalosis. Where metabolism is involved there would be definitely a need of buffer as within cells metabolism is associated with the release of protons (H⁺) i.e. decrease in pH or uptake of protons (H⁺) i.e. increase in pH. Important buffers that are dominant in human body are

1.      Bicarbonate buffers

2.      Phosphate buffers

3.      Protein buffers

Different factors are involved in choosing a buffer for a particular biological reaction or biological sites. These factors include

·         Temperature

·         Desired pH

·         Toxicity to the system

·         Interactions of buffer with other biological components

1.1.               Bicarbonates buffers (Buffering in blood)

Blood is a biological fluid in which Carbonic acid and Hydrogen carbonate buffer system plays an important role in maintaining pH around 7.40. In this buffer, carbonic acid (H₂CO₃) act as a weak acid and hydrogen carbonate ion (HCO₃^-) act as conjugate base of a weak acid or salt of weak acid.

H₂CO₃ H⁺ + HCO₃^-

When there is excessive amount of H⁺ in the blood it is consumed by HCO₃^- forming carbonic acid that is a weak acid which does not alter the blood pH so much and when there is excessive amount of OH^- in the blood it is consumed by H₂CO₃ as it will release the H⁺ ions upon excess amount of OH^-  in the blood forming H₂O.

Proportion of carbonic acid and hydrogen carbonate is also very much important in blood. Carbonic acid concentration is controlled by respiration through lungs while hydrogen carbonate concentration is controlled by urination through kidneys.

Carbonic acid buffer system is a critical buffer for blood as in the absence of this buffer system the pH may fall below this normal value within blood producing a condition a condition called acidosis ( acidosis may be respiratory or metabolic acidosis) or the pH may rise above normal level producing a condition known as alkalosis (alkalosis may be respiratory or metabolic acidosis).

As most of the metabolic activities in the human body release acidic materials in the blood so to control acidic conditions the much higher concentration of hydrogen carbonate ion than carbonic acid in blood should be present as acidic materials will react with hydrogen carbonate to produce weak acid called carbonic acid that does not alter the pH of the blood to great extent.

1.2.         Phosphate buffer (Buffering of internal cell fluids)

The phosphate buffer system works in the internal fluid of all cells. This buffer system consists of dihydrogen phosphate ions (H₂PO₄^-) as a weak acid and hydrogen phosphate ions (HPO₄^2-) as a conjugate base of weak acid. These two ions are in equilibrium with each other as indicated by the chemical equation below.

H₂PO₄^- H⁺ + HPO₄^2-

If additional hydrogen ions enter the cellular fluid, they are consumed in the reaction with HPO₄^2-, and the equilibrium shifts to the left. If additional hydroxide ions enter the cellular fluid, they react with H₂PO₄^-, producing HPO₄^2-, and shifting the equilibrium to the right. In the absence of phosphate buffer from cell fluid, sharp changes in pH of cell fluids may cause cell death or improper working of different proteins and cell organelles present within the cell.

1.3.         Protein buffer (Buffering in Cells and Tissues)

Proteins are mainly composed of amino acids. These amino acids contain functional groups that act as weak acid and bases when there are sharp changes in pH in order to stabilize the pH within the body cells. In short it can be said that proteins act as buffers themselves. Protein is a significant buffer the main buffering site for protein is cells and tissues but even in blood it act as a buffer consuming hydrogen ions producing due to the dissociation of the carbonic acid into hydrogen bicarbonate. To understand the proteins as a buffer we have to look into the structure of amino acids which consists of

From the above four groups COOH and NH₂ act as buffer systems for acidic and basic conditions.

At a near neutral pH, like the pH of blood, the carboxyl group is actually COO^- instead of COOH. Then, if a protein finds itself in a more acidic solution, the carboxyl group will be able to take on the extra hydrogen ions and return to the COOH configuration.

At a near neutral pH, like in blood, the amino group is actually NH₃⁺ rather than just NH₂. It actually tends to carry an extra hydrogen ion on it at a normal pH. Then, if a protein finds itself in a more basic environment, its amino groups on its amino acids can actually release their hydrogen ions and return to NH₂. As all cells and tissues are composed of proteins mainly so in the absence of protein buffer the sharp changes in pH may cause cell death or tissue damage of a living organisms.