Hydrogen carbonate-carbonic acid buffer

In the human body, carbon dioxide provides the buffer. This is called the carbonic acid-hydrogen carbonate ion buffer system. This buffer system maintains the body s blood pH within acceptable levels. The main threat to the bloods pH is excess hydrogen ions produced by various chemical reactions in the body. When hydrogen ions are produced, hydrogen carbonate ions in the blood pick them up and convert them to carbonic acid ... 

The most important type of mixed solution is a buffer, a solution in which the pH resists change when small amounts of strong acids or bases are added. Buffers are used to calibrate pH meters, to culture bacteria, and to control the pH of solutions in which chemical reactions are taking place. They are also administered intravenously to hospital patients. Human blood plasma is buffered to pH = 7.4 the ocean is buffered to about pH = 8.4 by a complex buffering process that depends on the presence of hydrogen carbonates and silicates. A buffer consists of an aqueous solution of a weak acid and its conjugate base supplied as a salt, or a weak base and its conjugate acid supplied as a salt. Examples are a solution of acetic acid and sodium acetate and a solution of ammonia and ammonium chloride. 

This proton transfer reaction involves the second acidic hydrogen atom of carbonic acid, so the appropriate equilibrium constant is. a 2 > whose p is found in Appendix E p. a 2 — 10.33. Because this is a buffer solution, we apply the buffer equation ... 

Transfer the residue prepared as in Section 6.1.1 into a 300-nL separatory funnel with 25 mL of phosphate buffer solution (0.1 M, pH 7.4). Add 10 mL of saturated aqueous sodium chloride and 50 mL of 0.5 M sodium hydrogen carbonate to the funnel and shake the funnel vigorously for 1 min. Add 70 mL of ethyl acetate to wash the aqueous layer to the funnel, shake, separate, and discard the ethyl acetate layer. Repeat this extraction procedure three times. Add 2 mL of phosphoric acid and 20 mL of an acetate buffer solution (0.1 M, pH 4) to the aqueous layer and extract the mixmre with 50 mL of ethyl acetate three times. Combine the extracts and filter into a 500-mL round-bottom flask through 60 g of anhydrous sodium sulfate supported by a plug of cotton wool in a funnel. Concentrate the filtrate to dryness under reduced pressure. 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

Acid-base reactions of buffers act either to add or to remove hydrogen ions to or from the solution so as to maintain a nearly constant equilibrium concentration of H+. For example, carbon dioxide acts as a buffer when it dissolves in water to form carbonic acid, which dissociates to carbonate and bicarbonate ions ... 

The principal buffer system in blood serum is based on the equilibrium between carbonic acid, H2C03(aq), and the hydrogen carbonate ion, HCO3 . Carbonic acid is unstable, however. It is also in equilibrium with carbon dioxide. Therefore, a second equilibrium reaction is involved in the hydrogen carbonate buffer system in the blood the reaction between carbon dioxide and water to produce carbonic acid, and its reverse. The two equilibrium reactions are summarized below. 

The sodium acetate-acetic acid combination is one of the most widely used buffers, and is usually referred to simply as acetate buffer. Other buffer combinations commonly employed in chemistry and biochemistry include carbonate-bicarbonate (sodium carbonate-sodium hydrogen carbonate), citrate (citric acid-trisodium citrate), phosphate (sodium dihydrogen phosphate-disodium hydrogen phosphate), and tris [tris(hydroxymethyl)amino-methane-HCl]. 

Hydrazines with at least one hydrogen substituent on nitrogen are oxidised in aqueous solution to the substituted diazene. Oxidation takes place in both acid and basic solution. Phenylhydraziiie is oxidised by inorganic reagents such as iodine buffered by sodium hydrogen carbonate to form benzenediazonium ion. The latter combines with the substrate to form the isolated product [140]. 1,1-Disubstituted... 

Predict the pH region in which each of the following buffers will be effective, assuming equal molarities of the acid and its conjugate base (a) sodium nitrite and nitrous acid (b) sodium formate and formic acid (c) sodium carbonate and sodium hydrogen carbonate (d) ammonia and ammonium chloride ... 

Activation energies for unimolecular 1,3-hydrogen shifts connecting ketones and enols are prohibitive, so that thermodynamically unstable enols can survive indefinitely in the gas phase or in dry, aprotic solvents. Ketones are weak carbon acids and oxygen bases enols are oxygen acids and carbon bases. In aqueous solution, keto-enol tautomerization proceeds by proton transfer involving solvent water. In the absence of buffers, three reaction pathways compete, as shown in Scheme 2. 

The oxidation of oximes offers an attractively simple route to nitroalkanes from carbonyl compounds. The most effective reagent is pertrifluoroacetic acid in acetonitrile in the presence of sodium hydrogen carbonate as a buffer. Yields are improved by the addition of small quantities of urea to remove oxides of nitrogen. The reaction is illustrated by the conversion of dipropyl ketoxime into 4-nitroheptane (Expt 5.190). 

V-Formylkynurenine is one of the 16 autoxidation products of tryptophan (51) (Fig. 8). The dye-sensitized photo-oxygenation of tryptophan in sodium carbonate - acetic acid buffer (pH 7) gave TV-for my Iky n urenine as the major product (52). This is also the oxidation product of tryptophan with hydrogen peroxide (53) and with ozone (54). This is an interesting case the same degradation impurity can be obtained in different ways, probably... 

The fact that the hydrogen ion is an important chemical species in these reactions is indicative of the major role that carbonic acid plays in influencing the pH and buffer capacity of natural waters. Furthermore, the activity of the carbonate anion in part determines the degree of saturation of natural waters with respect to carbonate minerals. Determination of the activity or concentration of CO32- is not an easy task nevertheless, it is necessary to the interpretation of a myriad of processes, including carbonate mineral and cement precipitation-dissolution and recrystallization reactions. 

In summary, peracetic acid in aqueous solution is an efficient reagent for the epoxidation of a variety of substrates, however, it should be used relatively quickly after its preparation. Sensitive substrates like isoamylene also require a buffer such as sodium hydrogen carbonate to affect high yield of the epoxide. Solvent extraction of an appropriate source of a peracid can lead to organic solutions of the oxidation species. Such methods have been available for many years,43 however, very few are amenable to more than a small scale operation. 

This reaction prevents a large pH drop in the system. A similar buffering behavior is observed when a base is added to the buffer solution. Here, the OH of the base reacts with the acid, forming more hydrogen carbonate ions ... 

---