Answer to: A buffer solution contains 0.477 M NH4Cl and 0.356 M NH3 (ammonia). Figure 12.3 The Molecular Structure of Aspirin. Aspirin is well known as a pain reliever and antipyretic (fever reducer). The Kb Of Ammonia Is 1.8 X 10-5. (Technically, a buffer can be made from any two components.). The compound CH 3 NH 3 Cl is a salt made from that weak base, so the combination of these two solutes would make a buffer solution. Because the acid properties of aspirin may be problematic, many aspirin brands offer a “buffered aspirin” form of the medicine. In this equation H2O is the conjugate acid and its corresponding conjugate base is OH− while NH3 and NH4+ represent the base and its conjugate acid pair. A buffer is an aqueous solution that can resist significant changes in pH levels upon the addition of small amount of acid or alkali. 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. Define buffer. Once either solute is completely reacted, the solution is no longer a buffer, and rapid changes in pH may occur. One buffer in blood is based on the presence of HCO3− and H2CO3 [the second compound is another way to write CO2(aq)]. Which solution should have the larger capacity as a buffer? Every buffer is made up of a conjugate acid-base pair. When HCl (strong acid) is added to this buffer system, the extra H+ ions added to the system are consumed by the NH3 to form NH4+. Can a buffer be made by combining a strong acid with a strong base? The complete phosphate buffer system is based on four substances: H3PO4, H2PO4−, HPO42−, and PO43−. 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. Question: Calculate The PH Of The 0.30 M NH3/0.36 M NH4Cl Buffer. Inside many of the body’s cells, there is a buffering system based on phosphate ions. Question: A) What Will Be The PH Change When 20.0 ML Of 0.100 M NaOH Is Added To 80.0 ML Of A Buffer Solution Consisting Of 0.164 M NH3 And 0.182 M NH4Cl? 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−. What different buffer solutions can be made from these substances? The acid part is circled; it is the H atom in that part that can be donated as aspirin acts as a Brønsted-Lowry acid. If 1 mL of stomach acid [approximated as 0.1 M HCl(aq)] were added to the bloodstream and no correcting mechanism were present, the pH of the blood would decrease from about 7.4 to about 4.7—a pH that is not conducive to continued living. Explain why NaBr cannot be a component in either an acidic or a basic buffer. A very commonly used example of an alkaline buffer solution is a mixture of ammonia and ammonium chloride solution. Figure 12.2 "The Actions of Buffers" illustrates both actions of a buffer. Buffers can react with both strong acids (top) and strong bases (side) to minimize large changes in pH. Which combinations of compounds can make a buffer? A solution that resists dramatic changes in pH. 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. By definition, strong acids and bases can produce a relatively large amount of H+ or OH− ions and consequently have marked chemical activities. As useful and common as aspirin is, it was formally marketed as a drug starting in 1899. For each combination in Exercise 4 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. It is generally made from a weak acid and one of its salts (often called conjugate*). Why or why not? NH 3 is a weak base, but NaOH is a strong base. Correctly identify the two components of a buffer. A buffer is a solution that resists changes in pH when small amounts of H+ or OH- are added. For example, in a buffer containing NH3 and NH4Cl, NH3 molecules can react with any excess H+ ions introduced by strong acids: while the NH4+(aq) ion can react with any OH− ions introduced by strong bases: Which combinations of compounds can make a buffer solution? Let us use an HC2H3O2/NaC2H3O2 buffer to demonstrate how buffers work. Which solution should have the larger capacity as a buffer? PKa = 9.25 B) Because HC2H3O2 is a weak acid, it is not ionized much. HCl is a strong acid, not a weak acid, so the combination of these two solutes would not make a buffer solution. However, recently aspirin has been touted for its effects in lessening heart attacks and strokes, so it is likely that aspirin is here to stay. 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. For example, a buffer can be composed of dissolved HC2H3O2 (a weak acid) and NaC2H3O2 (the salt derived from that weak acid). As indicated in Section 12.4 "Strong and Weak Acids and Bases and Their Salts", weak acids are relatively common, even in the foods we eat. The amount of strong acid or base a buffer can counteract. *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. If these were mixed in equal molar proportions, the solution would have a pH of 9.25. You can change the pH of the buffer solution by changing the ratio of acid to salt, or by choosing a different acid and one of its salts.
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