Experiment 7 Acid-Base Titration

Morel, J.-P. et al.. Effect of temperature on the acid-base properties of the alumina surface Microcalorimetry and acid-base titration experiments, J. Colloid Interf. Sci., 298, 773, 2006. 

In this experiment the overall variance for the analysis of potassium hydrogen phthalate (KHP) in a mixture of KHP and sucrose is partitioned into that due to sampling and that due to the analytical method (an acid-base titration). By having individuals analyze samples with different % w/w KHP, the relationship between sampling error and concentration of analyte can be explored. 

A 100-gal pilot-plant reactor is agitated with a six-blade pitched turbine of 6 in diameter that consumes 0.35 kW at 300 rpm. Experiments with acid-base titrations showed that the mixing time in the vessel is 2 min. Scale up to a 1000-gal vessel with the same mixing time is desired. 

Experiment 7 Determination of Concentration by Acid-Base Titration... 

Experiment 11 Determination of Appropriate Indicators for Various Acid-Base Titrations... 

In an acid-base titration you may either add acid to base or base to acid. This addition continues until there is some indication that the reaction is complete. Often a chemical known as an indicator will indicate the endpoint of a titration reaction, the experimental end of the titration. If we perform the experiment well, the endpoint should closely match the equivalence point of the titration, the theoretical end of the reaction. All the calculations in this section assume accurate experimental determination of the endpoint, and that this value is the same as the equivalence point. 

In this experiment the neutralizing power of various antacids will be determined. Antacids contain basic compounds that will neutralize stomach acid (stomach acid is HC1). The amount of base in the antacid tablets will be determined by an acid-base titration. It is a back titration method. This method is used because most antacids produce carbon dioxide gas, which can interfere with the titration. By initially adding an excess of acid, one can drive off the C02 by boiling the solution before titrating the excess acid. There are many brands of commercial antacids with various ingredients. A few of the common ones are listed below ... 

This experiment is an acid-base titration similar to those performed in Chapters 4 and 5. It is the titration of 0.10 M HC1 with 0.10 M NaOH, as in Experiment 8, but a combination pH probe will be used to monitor the pH during the titration, as in Experiment 10. The pH meter to be used has an RS232 output to interface with a microcomputer. We will use this special feature of the pH meter to feed the pH data directly to a microcomputer in an example of data acquisition by computer, and observe the titration curve traced on the screen in real time. 

It is possible to monitor the course of a titration using potentiometric measurements. The pH electrode, for example, is appropriate for monitoring an acid-base titration and determining an end point in lieu of an indicator, as in Experiment 10 in Chapter 5. The procedure has been called a potentiometric titration and the experimental setup is shown in Figure 14.11. The end point occurs when the measured pH undergoes a sharp change—when all the acid or base in the titration vessel is reacted. The same... 

A student performed an acid-base titration. The student began Part I of the experiment by determining the exact concentration of a base through the standardization of a basic solution using a primary acidic HCl standard. The student measured out approximately 10 mL of 6.00 M NaOH and diluted it to approximately 600 mL. The student discovered that 48.7 mL of the NaOH solution was needed to neutralize exactly 50.0 mL of a 0.100 M HCl solution. 

A student performed an acid-base titration. The student began Part I of the experiment by determining the exact concentration of a base through the standardization of a basic solution using a primary acidic HCl standard. 

In Acid-Base Titration and the Global Carbon Cycle, the scenario and the application laboratory were developed in conjunction with a field ecologist who simply stated, We can have the students set up in the laboratory what we have done in the field. They just have to set up an apparatus that traps the leaves and collects the C02. This experi-... 

It has been well known for a relatively long time that micellar, i.e. association colloidal, systems have a considerable effect on such indicator equilibria. Indeed, in the 1920 s and early 1930 s experiments were carried out in order to elucidate the so-called colloid or indicator error (Hartley, 1934 Hartley and Roe, 1940). In addition, the protein error was noted in investigations involving acid-base titrations in the presence of proteins (Sorensen, 1929 cf. Hartley, 1934). These errors are, of course, the consequence of micellization and the subsequent effects of micelles on equilibrium (34). The importance of many indicators in the dye, textile, and photographic industries, and the analytical utility of the shifts in indicator equilibria prompted much of the research in this area. 

Skills Toolkit 1, on the next two pages, has step-by-step instructions to help you carry out an acid-base titration. Study and understand all of the steps before you start to perform a titration experiment. If your attention alternates between book and buret, you re likely to make mistakes. Experience helps, and your second titration should be much better than your first. 

According to Chapter 11, an acid is a substance that upon dissolving in water increases the concentration of hydronium (H30 ) ions above the value found in pure water, and a base is a substance that increases the concentration of hydroxide (OH ) ions above its value in pure water. Despite the careful language, it is commonplace to view acids and bases as substances that dissociate to give protons (which upon hydration become hydronium ions) and hydroxide ions, respectively. If the dissociation is complete, we can easily calculate the concentration of hydronium and hydroxide ions in the solution and then calculate the yield of acid-base neutralization reactions, and acid-base titrations, by the methods of stoichiometry in solution. But experience shows that many acid-base reactions do not go to completion. So, to predict the amount (or concentration) of... 

It is important to know the dissociation constant of an indicator in order to use it properly in acid-base titrations. Spectrophotometry can be used to measure the concentration of these intensely colored species in acidic versus basic solutions, and from these data the equilibrium between the acidic and basic forms can be calculated. In one such study on the indicator wj-nitrophenol, a 6.36 X 10 M solution was examined by spectrophotometry at 390 nm and 25°C in the following experiments. In highly acidic solution, where essentially all the indicator was in the form HIn, the absorbance was 0.142. In highly basic solution, where essentially all of the indicator was in the form In , the absorbance was 0.943. In a further series of experiments, the pH was adjusted using a buffer solution of ionic strength I, and absorbance was measured at each pH value. The following results were obtained ... 

Koretsky et al. calculated site densities for particular low index faces of six oxides and six silicate minerals and average site densities for cleavage and growth faces, and showed that these methods lead to very different results. Full documentation of depth, length of broken bond and Brown bond strengths of broken bonds for particular types of sites is presented. The ranges of TVs calculated by Koretsky et al. [7] and in their literature data collection (tritium exchange, acid-base titrations, NMR, adsorption and desorption of water at various conditions, and saturation experiments with different adsorbates in solution) for six oxides are listed in Table 5.1. 

To obtain reliable data we need to carry out well-defined procedures, whose operational details depend on the goal of the experiment. Imagine, for example, that our problem is to determine the concentration of acetic acid in a vinegar sample. Traditionally, this is done with an acid-base titration. Following the usual method, we need to... 

Santschi, P., U. P. Nyffeler, R. F. Anderson, S. L. Schiff, P. O Hara R. H. Hesslein, 1984. Response of radioactive trace metals to acid-base titrations in controlled experimental ecosystems evaluation of transport parameters for application to whole lake radiotracer experiments. Can. J. Fish. Aquat. Sci. 43 60-77. 

By referring to Experiment 25 (Acid-Base Titration and Molecular Weight of an Unknown Acid), devise a reasonable method for determining the molecular weight of aspirin. Your instructor must approve an outline of your method and the quantities you plan to use before you begin work. The pKa... 

Experience shows marked deviation from the Henderson-Hasselbalch equation. There are examples of acid-base titration curves with curves broader than predicted by the Henderson-Hasselbalch equation, an effect called negative cooperativity, and there are examples of acid-base titration curves with curves sharper than predicted by the Henderson-Hasselbalch equation, an effect called positive cooperativity. These deviations from Equation (5.16) can be demonstrated by cooperative interactions involving the charged functional group. 

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