Preparing Buffers

Buffers are usually prepared by starting with a measured amount of either a weak acid (HA) or a weak base (B). Then OH is added to HA to make a mixture of HA and A (a buffer) or H is added to B to make a mixture of B and BH (a buffer). 

How many milliliters of 0.500 M NaOH should be added to 10.0 g of tris hydrochloride (BH, Equation 9-3) to give a pH of 7.60 in a final volume of 250 mL  

The Henderson-Hasselbalch equation allows us to find x, because we know pH and pATai 

To solve for x, raise 10 to the power of the terms on both sides, remembering that 10 °g = z  

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Multiprotic weak acids can be used to prepare buffers at as many different pH s as there are acidic protons. For example, a diprotic weak acid can be used to prepare buffers at two pH s and a triprotic weak acid can be used to prepare three different buffers. The Henderson-Hasselbalch equation applies in each case. Thus, buffers of malonic acid (pKai = 2.85 and = 5.70) can be prepared for which... 

In the laboratory, chemists prepare buffer solutions in three different ways. Each results in a solution containing a weak acid and its conjugate base as major species. The most straightforward way to produce a buffer solution is by dissolving a salt of a weak acid in a solution of the same weak acid, as described in Example. ... 

C18-0006. Which of the following sets of chemicals can be used to prepare buffer solutions For each one that can, specify the weak acid and its conjugate base that are major species in the buffer solution (a) HCl and KCl (b) HCl and KNO2 (c) HCl and NH4 Cl (d) NaOH and Na2 HPO4 and (e) NaCl and NaC2 H3 O2. 

C18-0051. Which of the following sets of chemicals can be used to prepare buffer solutions For each one... 

Serum samples are prepared for assay by a modification of a previous method serum is used instead of whole blood (B18, T3). Serum is diluted 1 10 with buffer at pH 6.1 to which fresh 0.05% ascorbic acid has been added. To prepare buffer dissolve 27.8 g of NaH2P04 H20 in 1000 ml distilled water (Solution 1) dissolve 71.7 g Na2HP0412 H20... 

Procedure Weigh accurately about 0.1 g of benzylpenicillin in DW and dilute to 100 ml in a volumetric flask. Transfer 10.0 ml to an iodine flask, add 5 ml of N sodium hydroxide and allow to stand for 20 minutes. Now, add 20 ml of freshly prepared buffer solution, 5 ml of N HC1 and 25.0 ml of 0.02 N iodine solution. Close the flask with a wet glass-stopper and allow to stand for 20 minutes in a dark place (i.e., protected from light). Titrate the excess of iodine with 0.02 N sodium thiosulphate, employing freshly prepared starch solution as an indicator added towards the end-point. 

Sodium acetate is a mordant in dyeing. Other applications are in photography, as an additive to food, in purification of glucose, in preservation of meat, in tanning, and as a dehydrating agent. In analytical chemistry it is used to prepare buffer solution. 

Some weak acids and bases have more than one buffer range, for example phosphoric acid has three ionisable protons with three different pA"a values and can be used to prepare buffers to cover three different pH ranges. The ionic species involved in the ranges covered by phosphate buffer are ... 

Buffer Solutions, Prepare buffer solns of the following pH s at 25° C by mixing the... 

Logarithms to the base 10 are used in both equations. These equations are useful in preparing buffers and in thinking about what fraction of a substance exists in a given ionic form at a particular value of pH. From Eq. 3-7 it is easy to show that when the pH is near the pKa relatively large amounts of acid or base must be added to change the pH if the concentrations of the buffer pair A and HA are high. 

To prepare buffers with pH intermediate between the points listed in Table A.2A.4, prepare closest higher pH, then titrate with solution A. 

FIGURE 16.5 Prepackaged buffer solutions of known pH, and solid ingredients for preparing buffer solutions of known pH. 

The pH s of Tris-based buffers are sensitive to temperature changes. Always prepare buffers at the same temperature in which they will be used, and be aware that refrigeration and heating can cause changes in the pH of temperature-sensitive buffers. Always allow reagents to equilibrate to room temperature before use. 

Calculate the pH and acetate ion concentration when a buffer solution is prepared by mixing 400 ml of 0.1 M formic acid and 200 ml of 0.1 M sodium acetate. The pKa values of formic and acetic acid are 3.75 and 4.76, respectively. Is there an advantage to preparing buffers of this sort as opposed to simple acetate and formate buffers ... 

Cacodylic acid, (CH3)2As02H, is a toxic compound that behaves as a weak acid. It is used to prepare buffered solutions. For the following reaction pKa = 6.19 ... 

Pre-prepared buffers for metal-ion determinations are commercially available from a range of suppliers. 

Listed below are some acids and bases that are useful in preparing buffers for enzyme assays. The choice of a particular compound depends on many factors. For example, multicarboxylic acids would be poor choices for reactions involving metal ions as cofactors amino acids may be poor choices for reactions involving amino acids as substrates. The number of buffer components can be kept to a minimum by using an acid and a base to cover the desired region. For example, maleic acid and Tris can be mixed to produce Tris-maleate buffers of pH 5.7 to 8.6 (rather than using maleic acid-NaOH and Tris-HCl). 

A solution of a weak acid and its salt (conjugate base) or a weak base and its conjugate acid acts as a buffer solution. The quantities of buffer components required to prepare buffers solutions of known pH can be calculated from the Henderson-Hasselbalch equation. The buffering capacity of a buffer solution is maximum at the pK of the weak acid component of the buffer. Universal buffers are mixtures of polybasic and monobasic acids that are effective over a wide range of pH. 

NH4F is commonly used to prepare buffered solutions for etching of silicon and its oxides. For NH4F-buffered HF solutions, the equilibrium is further complicated by the reaction... 

Control of pH is vital in synthetic and analytical chemistry, just as it is in living organisms. Procedures that work well at a pH of 5 may fail when the concentration of hydronium ion in the solution is raised tenfold to make the pH 4. Fortunately, it is possible to prepare buffer solutions that maintain the pH close to any desired value by the proper choice of a weak acid and the ratio of its concentration to that of its conjugate base. Let s see how to choose the best conjugate acid-base system and how to calculate the required acid-base ratio. 

The label should indicate if a tablet or capsule contains one, two or three adult standard dosage forms of the drug. Liquid preparations should indicate similarly if there is one, two or three adult standard dosage forms per teaspoon of the preparation. Buffered salicylate products must have at lezist 1.9 milliequiveilent of acid neutralising capacity per adult dosage unit. 

Triton X-100 (Sigma-Aldrich, Athens, Greece). Triton is used as a 10% v/v solution in the liposome preparation buffer (see below). Usually 1 L solution is prepared, stored at room temperature and used for up to 3 months. 

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