Chemical reactions acid-base neutralization

We now discuss chemical reactions in further detail. We classify them as oxidation-reduction reactions, combination reactions, decomposition reactions, displacement reactions, and metathesis reactions. The last type can be further described as precipitation reactions, acid-base (neutralization) reactions, and gas-formation reactions. We will see that many reactions, especially oxidation-reduction reactions, fit into more than one category, and that some reactions do not fit neatly into any of them. As we study different kinds of chemical reactions, we will learn to predict the products of other similar reactions. In Chapter 6 we will describe typical reactions of hydrogen, oxygen, and their compounds. These reactions will illustrate periodic relationships with respect to chemical properties. It should be emphasized that our system is not an attempt to transform nature so that it fits into small categories but rather an effort to give some order to our many observations of nature. 

The last definition has widespread use in the volumetric analysis of solutions. If a fixed amount of reagent is present in a solution, it can be diluted to any desired normality by application of the general dilution formula V,N, = V N. Here, subscripts 1 and 2 refer to the initial solution and the final (diluted) solution, respectively V denotes the solution volume (in milliliters) and N the solution normality. The product VjN, expresses the amount of the reagent in gram-milliequivalents present in a volume V, ml of a solution of normality N,. Numerically, it represents the volume of a one normal (IN) solution chemically equivalent to the original solution of volume V, and of normality N,. The same equation V N, = V N is also applicable in a different context, in problems involving acid-base neutralization, oxidation-reduction, precipitation, or other types of titration reactions. The justification for this formula relies on the fact that substances always react in titrations, in chemically equivalent amounts. 

When acids and bases come into contact with one another, a chemical reaction called a neutralization reaction takes place. A neutralization reaction is a double displacement reaction. In a double displacement reaction, the positive ions from one reactant take the place of the positive ions in the other reactant. For example, if hydrochloric acid and sodium hydroxide react with one another, the positive sodium ion in sodium hydroxide will take the place of the hydrogen ion in the hydrochloric acid ... 

Normality applies mostly to acid-base neutralization, but the concentrations of other chemicals used in other kinds of reactions, such as in oxidation-reduction reactions, may also be expressed in normality. 

There are some cases where a reaction, that is, the formation or dissolution of a chemical bond, is involved along with ion exchange phenomena (Helfferich, 1983). Examples of this are acid-base neutralization, dissociation of weak electrolytes in solution or weak ionogenic groups in ion exchangers, complex formation, or combinations of these (Table 5.2). With some of these, very low apparent D in ion exchangers have been noted. 

The addition of a strong base to a strong acid (or the reverse) is the simplest type of titration. The chemical reaction is the neutralization ... 

Mixing effects can change the apparent kinetics of the reaction so that the measured kinetics is limited by the rate of mixing rather than by the rate of reaction. This problem is so pervasive that the rate of mixing for fast reactions is often mistaken for the rate of a chemical reaction. For a very fast chemical reaction, for example, an acid-base neutralization with a half-life of 0.001 sec, the rate of the chemical reaction depends on the rate of the mixing, which is much slower. If the reaction rate was measured, the result would be the mixing rate and not the molecular chemical reaction rate. The result is the apparent reaction rate. 

The donor-acceptor principle is an important basic concept in modern chemical education acid-base reactions, redox reactions and complex reactions explain a huge number of chemical changes. One important group of donor-acceptor reactions are the acid-base reactions protons (H+ ions) transfer from one species to another species. One example, in the neutralization of sulfuric acid with sodium hydroxide a proton is moving from one hydronium ion H30 + (aq) of the acid solution to one hydroxide ion OH (aq) ion of the hydroxide solution. Broensted s key concept will be considered in this chapter. 

Rules for Reactivity Prediction. Rules for predicting reactivity of given chemical species were developed as simply as possible, in order that they would be appropriate for later pedalogical use. The use of reduction potentials for the prediction of redox reactions has already been mentioned, as has the use of pKa and pKfe values to satisfy the rule that the strongest acid will react with the strongest base to undergo acid-base neutralization reactions. 

Quantitative studies of acid-base neutralization reactions are most conveniently carried out using a technique known as titration. In titration, a solution of accurately known concentration, called a standard solution, is added gradually to another solution of unknown concentration, until the chemical reaction between the two solutions is complete. If we know the volumes of the standard and unknown solutions used in the titration, along with the concentration of the standard solution, we can calculate the concentration of the unknown solution. 

In order to analyze energy changes associated with chemical reactions we must first define the system, or the specific part of the universe that is of interest to us. For chemists, systems usually include substances involved in chemical and physical changes. For example, in an acid-base neutralization experiment, the system may be a beaker containing 50 mL of FlCl to which 50 mL of NaOFl are added. The surroundings are the rest of the universe outside the system. 

It is important to realize that the fact that a process is spontaneous does not necessarily mean that it will occur at an observable rate. A chemical reaction is spontaneous if it occurs on its own accord, regardless of its speed. A spontaneous reaction can be very fast, as in the case of acid—base neutralization, or very slow, as in the rusting of iron. Thermodynamics tells us the direction and extent of a reaction but nothing about the speed. 

One requirement for a reaction to occur is that the chemicals involved must be able to mix and interact with one another. Thus the physical state of the reactants can be important. In particular, an aqueous solution is often used as the medium for a reaction. To describe reactions in the aqueous phase effectively, we often need to specify the molar concentration of the solutions used. We also have options about how to write the chemical reaction itself—as a molecular equation, for example, or a net ionic equation. Several classes of chemical reactions, such as precipitation reactions or acid-base neutralizations, are sufficiently common that additional definitions have been established to improve our ability to communicate about them. 

There is very little published on chemical reactions occurring at the polymer/water interface in polymer colloids beyond the simple acid-base neutralizations of the counterions mentioned above. Some evidence has been developed to indicate that certain secondary reactions must have occurred either during the emulsion polymerization or subsequently on storage. 

Among them, volumetric methods are presumably the most widely used for water analysis. They are titrimetric techniques which involve a chemical reaction between a precise concentration of a reagent or titrant and an accurately known volume of sample. The most common types of reactions as used within this method are acid-base neutralization, oxidation-reduction, precipitation, and complexation. The use of an indicator which identifies the equivalence point is required to develop this kind of method. The modem laboratories usually employ automated endpoint titrators, which largely improve the efficiency and reliability of the determination. Moreover, spectrophotometric, potentiometric, or amperometric methods to determine the endpoint of the reaction can... 

In Sections 4.2 and 4.3 we encountered two types of chemical reactions that can occur when two electrolyte solutions are combined precipitation, in which ionic compounds exchange ions, and acid-base neutralization, in which a proton is transferred from an acid to a base. In this section, we will learn about oxidation-reduction reactions, commonly called redox reactions. A redox reaction is a chemical reaction in which electrons are transferred from one reactant to another. For example, if we place a piece of zinc metal into a solution that contains copper ions, the following reaction will occur ... 

An important question for the design of continuous flow systems is When can the classic perfectly mixed assumption (ideal CSTR) be used in a continnons flow stirred tank reactor The blend time concept can be used here. If the blend time is small compared to the residence time in the reactor, the reactor can be considered to be well mixed. That is because the residence time is proportional to the characteristic chemical reaction time. A 1 10 ratio of blend time to reaction time is often used, but often, larger values result because the mixer must do other jobs, which lead to even smaller blend times. Frequently, residence time distributions are used to determine whether a reactor is well-mixed. It is usually easy to achieve well-mixed conditions in continuous flow, turbulent stirred vessels unless the reactions are very fast, such as acid-base neutralizations. Even in laminar systems the blend time can be made much less than the required residence time for the chemical reaction mainly because required residence times are so long for high viscosity reactants. For discussions of residence time distribution analysis, see Chapter 1, Levenspiel (1972), and Nauman (1982). 

Chitosan, a widely used natural biopolymer, has been studied for the adsorption of various metal ions from dilute solutions. Unfortunately, the inherent properties of chitosan, such as hydrophilicity and metal-binding capability, are often insufficient to meet the requirements of a number of applications. To improve these properties, both chemical and physical modifications of chitosan are required. Thus, Aliquat 336-functionalized chitosan as adsorbent was prepared. In fact, the new chitosan adsorbent can also be described as P-SIL containing quaternary ammonium ionic liquid [23]. Unlike the previous reported structure, the Aliquat 336-functionalized chitosan, which was prepared by acid/base neutralization reaction, consists largely of cations and anions (Fig. 5.12). The structure was so flexible that the adsorption ability could be controlled precisely. Moreover, incorporation of Aliquat 336 into the chitosan backbone could significantly enhance its metal ions extraction ability. It has been shown to have much improved affinity for Pb " than pure chitosan. This may be explained in that the new strategy doesn t reduce the original amino active sites besides, the synergistic effect between cation and anion also contributes to the enhancement of adsorption capabilities. On the other hand, the effort to increase selectivity of the adsorbent for one metal ion over others is to make the adsorbent sterically efficient with that metal ion only. The new chitosan-... 

Case 2 The gas-phase concentration here increases in the positive direction so that no transfer of solufe from gas to liquid can fake place. No transfer can occur in the opposite sense, because the liquid concentration rises in the negative direction. Such profiles arise only in cases when solufe is generated by chemical reaction af the gas-liquid interface. The producf solufe fhen diffuses from the interface info fhe bulk fluids using the profiles shown. The case is a relatively rare one because the products of a chemical reaction — typically an acid-base neutralization — tend to be nonvolatile and do not transfer back into tile gas phase. 

The dramatic way in which research chemists have recently discarded the apology that reactions such as acid-base neutralization are immeasurably fast or instantaneous should compel the attention of every student of chemistry. Developments in electronics during and since World War II have made the long needed snapshots of simple instantaneous chemical processes possible. However, if we do not bother with the distinction between fast and very fast chemical reactions, those having half-lives greater and less than 10 sec, respectively, the study of fast chemical reactions is a comparatively old one as topics in physical chemistry go. 

---