© 2019 Westlab Group Ltd. All rights reserved. Simply put, a buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. By definition, strong acids and bases can produce a relatively large amount of H+ or OH− ions and consequently have marked chemical activities. PKa = 9.25 B) A solution that resists dramatic changes in pH. *A conjugate acid is a species formed by the gain of a proton by a base while in reverse, a conjugate base is a species formed by the removal of a proton from an acid. HCl is a strong acid, not a weak acid, so the combination of these two solutes would not make a buffer solution. It is generally made from a weak acid and one of its salts (often called conjugate*). One solution is composed of NH3 and NH4NO3, while the other is composed of H2SO4 and Na2SO4. Buffers work by neutralizing any added acid (H+ ions) or base (OH- ions) to maintain the moderate pH, making them a weaker acid or base. Now there is a term we call, ‘Breaking of the buffer solution’ which arises when the entire base and its conjugate acid (in the above case NH3 and NH4+) are consumed to neutralize the added acid or base. Let’s take an example of a buffer made up of the weak base ammonia, NH3 and its conjugate acid, NH4+. (Technically, a buffer can be made from any two components.). Which solution should have the larger capacity as a buffer? Why or why not? Define buffer. Explain why NaBr cannot be a component in either an acidic or a basic buffer. Once either solute is completely reacted, the solution is no longer a buffer, and rapid changes in pH may occur. Let us use an HC2H3O2/NaC2H3O2 buffer to demonstrate how buffers work. Two solutions are made containing the same concentrations of solutes. The amount of strong acid or base a buffer can counteract. However, it is still an acid, and given that some people consume relatively large amounts of aspirin daily, its acidic nature can cause problems in the stomach lining, despite the stomach’s defenses against its own stomach acid. (Assume That There Is No Change In Total Volume When The Two Solutions Mix.) Thus the breaking of the buffer is its capacity, or in other words, it is the amount of acid or base, a buffer can absorb before breaking its capacity. For each combination in Exercise 3 that is a buffer, write the chemical equations for the reactions of the buffer components when a strong acid and a strong base is added. 3b: strong acid: NO2− + H+ → HNO2; strong base: HNO2 + OH− → NO2− + H2O; 3d: strong base: NH4+ + OH− → NH3 + H2O; strong acid: NH3 + H+ → NH4+, Buffers can be made from three combinations: (1) H3PO4 and H2PO4−, (2) H2PO4− and HPO42−, and (3) HPO42− and PO43−. If a strong acid—a source of H+ ions—is added to the buffer solution, the H+ ions will react with the anion from the salt. Which solution should have the larger capacity as a buffer? Two solutions are made containing the same concentrations of solutes. If a strong base—a source of OH−(aq) ions—is added to the buffer solution, those OH− ions will react with the HC2H3O2 in an acid-base reaction: Rather than changing the pH dramatically by making the solution basic, the added OH− ions react to make H2O, so the pH does not change much. The phosphate buffer should have the larger capacity. Similarly when NaOH (strong base) is added to this buffer system, the ammonium ion donates a proton to the base to become ammonia and water thus neutralizing the base without any significant pH change. The circled atoms are the acid part of the molecule. Each buffer is characterized by a set ‘capacity’ which is defined as the quantity of strong acid or base that must be added to change the pH of one liter of solution by one pH unit.
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