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Introduction

F7 Essay Writing (Buffer Solution) Q. Write an account of buffer solutions. Guidelines: In your answer you should consider, giving examples, (a) definition (b) their compositions --- weak acid and its salt (acidic buffer), e.g. CH3COOH / CH3COONa --- weak base and its salt (basic buffer), e.g. NH3 / NH4Cl (c) how they work --- equilibrium shift after addition of a small amount of strong acid / strong base to buffer, --- resistance to pH change upon addition of small amount of acid / base (d) their applications --- for checking indicator solution and calibrating pH meters --- for controlling solution pH for chemical / biochemical reactions, --- for preserving food (e) their importance in nature --- maintenance of blood pH __________________________________________________________________________ ~ Sample Essay ~ A buffer solution is one which resists changes in pH when small amounts of acid or alkali is added to it. It plays an important role in chemical processes where it is essential that a fairly constant pH is maintained. Buffer solutions could be classified into two types, namely acidic buffer and basic buffer solutions. ...read more.

Middle

Firstly, the ethanoic acid reacts with it and consumes the excess OH- ions: CH3COOH + OH- CH3COO- + H2O (eqn. 3) On the other hand, the hydroxide ions combine with the hydroxonium ions furnished by ethanoic acid (see eqn. 1) to form water. As soon as this happens, the equilibrium of eqn. 1 is disturbed and then it shifts to the right so as to replace the H3O+ in order to restore the equilibrium. This keeps on happening until most of the incoming OH- are removed, and the pH remains almost constant. Basic buffer solutions A basic buffer solution is one which has a pH higher than 7. They are commonly made from a weak alkali and its salt. A mixture of ammonia and ammonium chloride solutions is a typical example. Ammonia is a weak base, and the equilibrium position will be well to the left: NH3 + H2O NH4+ + OH- (eqn. 4) Adding ammonium chloride to this ammonia solution will shift the equilibrium position even further to the left, in accordance to Le Chatelier Principle. When a strong acid such as HCl is added to the buffer, there are two processes which can remove hydroxonium ions. ...read more.

Conclusion

In a good many of industrial and physiological processes, specific reactions occur at some optimum pH values. When the pH varies to any extent from the optimum value, undesirable reactions and effects may occur. For example, the pH of your blood lies at about 7.35. If this value drops below or rises above 7.0, the results are fatal. Fortunately our blood contains a buffering system which maintains the acidity at the proper level. The molecule of plasma proteins act as buffers as they bear both the carboxylic acid group (-COOH) and the basic amino group (-NH2). H2O + CO2 H2CO3 H+ + HCO3- (eqn. 7) The protein acts as a base, and thereby neutralizing the additional H+ ions formed at high concentration of CO2. Meanwhile, it can also function as an acid to remove the additional HCO3- ions. Hence, a fairly constant pH of blood is maintained. In conclusion, a solution of stable pH is always important in many chemical and biochemical processes, in which buffer solution undoubtedly plays an active role. Particularly, buffer solutions are important to human body: without the protection of the buffering system in our bodies, we could not eat and adsorb many of the acidic fruit juices and foods in our diet! ?? ?? ?? ?? 1/3 ...read more.

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