Strength of acids or bases

Cabbage Juice Color Relative Strength of Acid or Base... 

Differentiating solvent n. A solvent, which will discriminate among the strengths of acids or bases. 

Deciding whether reactants or products are favored in an acid-base reaction Given an acid-base reaction and the relative strengths of acids (or bases), decide whether reactants or products are favored. (EXAMPLE 163)... 

The pH depends on the concentration of the solution. The strength of acids or bases depends on the extent to which they dissociate in aqueous solution. 

To make neutrality more quantitative, it is useful to devise an expression of the strength of acid or base. This is pH. You might have heard an expression such as pH-balanced shampoo. Technically pH is equal to the negative of the logarithm of [H+], the molar concentration of H+. [Suppose that you dissolve a chemical species A in water. You would then obtain a solution of A in water (aqueous solution of A). Notation [A] is called the molar concentration of A and indicates how many moles of chemical species A in a solution of 1 Liter (L) (technically in units of mol/L)]. So pH is related to the concentration of H+ species (more precisely, H O ) in a solution, but not in a straight way. As you saw before, a number can be expressed as something like a x 10 . A small number or a large number is often expressed in this... 

The amphoteric character of water offers a way to standardize the strength of acids or bases. For that purpose, we consider how an acidic or basic substance reacts with water as a standard reaction partner following the general scheme Ai + H2O Bi + HsO. This equilibrium is characterized by an equilibrium constant K, the acid dissociation constant. Often the common logarithm of Ka, pfCA, is used. The corresponding formulation of the law of mass action is given Eq. (2.22). 

Each acid and base has its own ionization constant. Some acids (or bases) have two or three hydrogen (or hydroj l) ions per atom, each of which has its own constant. The ionization constant determines the pH for a given strength of acid or base. Consider the example of an acid... 

Experimental values of K, ATb vary over many orders of magnitude. Rather than deal with such an unwieldy range of values, it is more convenient to express strengths of acids or bases on a logarithmic scale. The logarithmic exponent (pAT) of a dissociation constant is defined as... 

Because of its relative simplicity HSAB principle is widely used to predict directions of different donor-acceptor reactions in liqnid media of different kind. However, in order to obtain correct results, not only the snbgronp acids and bases should be taken into account, but also the properties of reagents in a given solvent. If there are no considerable distinctions in the strength of acids or bases, then the nse of HSAB principle for estimation is sufficiently correct. If opposite is the case, a lot of exclusions should be considered. For example, aqueous solutions of mercury (II) chloride are known to interact with potassium iodide, but this interaction proceeds according to the HSAB concept predictions ... 

The type of data produced in a f.a.b. experiment is affected by the pH and ionic strength of the matrix. The former may be controlled either by the addition of acids or bases, although, in practice, it is usually preferable to keep the matrix acidic. The ionic strength is partly dictated by the purity of the sample (many biological compounds are still contaminated with salts, even after extensive purification) and partly by exogenous additives. Three additives are especially useful for carbohydrate work. They are as follows. 

Acid/hase potentiometry enables the surface charge density to be measured. This involves comparison of the titration curves obtained for the suspension of oxide at several different ionic strengths (10 10" M) with that of the electrolyte alone, followed by calculation of the net consumption of protons or hydroxyl ions (mol g ) at each pH. The data is presented as a plot of excess of acid or base (Fh - Toh ) mol g or mol m ) vs pH (adsorption isotherm) or as a plot of surface charge, cr, (coulombs m ) vs pH (charging curve) (Figure 10.5). 

In the Bronsted definition, an acid donates a proton and a base accepts a proton. The strengths of acids and bases are measured by the extent to which they lose or gain protons, respectively. In these reactions acids are converted to their copjugate bases and bases to their conjugate acids. Acid-base reactions go in the direction of forming the weaker acid and the weaker base. 

Relative quantitative strengths of acids and bases are given either by their ionization constants, and K, or by their pK and pK values as defined by ... 

We can use the information in Tables 10.1 and 10.2 to determine the relative strengths of acids and bases in solution. For example, suppose we need to decide which member of (a) HF or HI03 (b) NOz or CN is the stronger acid or base in water. We need to know that the higher the K, of a weak acid, the stronger the acid and the weaker its conjugate base. Similarly, the... 

At present the dye techniques are very useful and economical but are somewhat approximate. Advances in use of indicator dyes for measuring surface acidity and basicity may be expected to include a two-parameter measure of acid or base strength similar to the E and C equation of Drago, and the use of fluorescent indicators for colored solids. 

The acid and base sensitivity of condensation polymers whether or not under stress, e.g. polycarbonate, polyesters, polyamides and polysilanes under influence of acid or base the condensation bonds are hydrolysed under the cooperative action of mechanical stresses and the environment. A striking example is shown in Fig. 26.11, where the strength retention of PpPTA fibres is plotted versus pH after an exposure of 3 months at room temperature (Van den Heuvel and Klop). The hydrolysis of the polyamide is acid or alkali catalysed, in particular below pH = 3 and above pH = 9. 

Adsorption of ETES and VTES on Alumina. In the absence of acid or base catalysts it was not possible to obtain ETES films on a-alumina by retraction and the VTES films were unstable toward the organic test liquids as well as water. This failure of both the ETES and VTES to form strongly held films can be attributed to the weakly basic character of alumina surfaces. The isoelectric point of alumina is usually at a pH of 7.5 to 9.0 (11) which is a rough measure of the base strength of the —A1—OH surface groups. Silica, on the other hand, has an isoelectric point at a pH of 2, signifying a moderately strong acid character for the... 

ACID-BASE DISSOCIATION EQUILIBRIA. STRENGTH OF ACIDS AND BASES The dissociation of an acid (or a base) is a reversible process to which the law of mass action can be applied. The dissociation of acetic acid, for example, yields hydrogen and acetate ions ... 

These equations represent a transfer of a proton from A, (Acid,) to B2 (Base2). Reactions between acids and bases are hence termed protolytic reactions. All these reactions lead to equilibrium, in some cases the equilibrium may be shifted almost completely in one or another direction. The overall direction of these reactions depends on the relative strengths of acids and bases involved in these systems. 

The great merit of glass and porcelain apparatus is that it can be employed with any strength of acid and base it is also preferred when weakly coloured compounds (especially yellow) are produced or when the test depends upon... 

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