Dissociation equations, strong bases

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

As the salt solution has a pH >7, it is the salt of a weak acid and strong base. The strong base is KOH and, as it is fully ionised, we cannot write an equilibrium equation for its dissociation. 

As potassium sorbate forms an alkaline solution in water, it is the salt of a weak acid and a strong base. Therefore sorbic acid must be a weak acid. (It is not necessary to know its formula or write an equation for its dissociation to be able to state that it must be a weak acid.)... 

For the reaction of a weak acid with a strong base, a similar neutralization occurs, but we must write the molecular formula of the acid rather than simply H + (aq), because the dissociation of the acid in water is incomplete. Instead, the acid exists primarily as the neutral molecule. In the reaction of HF with KOH, for example, we write the net ionic equation as... 

Because NaOH and Ca(OH)2 are strong bases, they are 100% dissociated and their [OH ] is directly related to their initial concentrations. To calculate the [OH ] in a solution prepared by dissolving CaO, we must first do a mass-to-mole conversion and then use the balanced equation for the reaction of CaO with water to find the number of moles of OH-in the solution. In each case, [H30 + ] = Kw/[OH-] and pH = — log[H30 + ]. 

I. Salt of Weak Acid and Strong Base.—When a salt, e.g., NaA, of a weak acid HA is dissolved in water, it may be regarded as undergoing complete dissociation into Na and A ions, provided the solution is not too concentrated. Since HA is a weak acid the conjugate base A will be moderately strong hence the latter will react with the solvent molecules (II2O) giving the type of hydrolytic equilibrium represented by equation (15) in the particular case of water as solvent, this may be written... 

IV. Very Weak Acid and Strong Base.—For very weak acids, whose dissociation constants are less than about 10, or for very dilute solutions, e.g., more dilute than 0.001 n, of weak acids, the pH of the solution exceeds 10 before the equivalence-point is reached. It is then necessary to include coh in B, although Cu can be neglected equation (39) then takes the form... 

The explanation of this striking regularity follows at once from the theory of electrolytic dissociation. According to this, theory the neutrahsation of a strong base with a strong acid is due simply to the combination of H and OH ions to form undissociated water according to equations such as... 

Nevertheless, calcium hydroxide and other slightly soluble metallic hydroxides are considered strong bases because all of the compound that dissolves is completely dissociated. The dissociation equations for several strong bases are hsted in Table 19-3. 

Write the equation for the dissociation of Ba(OH)2, and construct the reaction summary. Ba(OH)2 is a strong base that is completely dissociated. 

Acids will dissociate into hydrogen ions, i.e., protons, and their matching anions. Bases will dissociate into a cation and a hydroxyl anion. If the acid or base is a strong acid or strong base, then the dissociation is complete. Weak acids and weak bases dissociate only partially. How much is defined by the dissociation constant of the acid or base. When expressed as the negative logarithm of the proton concentration in equivalents/liter, it is called the pK of the acid or base. Therefore, in a solution of a weak acid, three participants are present proton, matching anion, and the undissociated parent weak acid. Similarly, a solution of a weak base contains a cation, a hydroxyl anion, and the undissociated parent base. How much of each is defined by the pH of the solution and the pK of the respective acid or base The Henderson-Hasselbalch equation defines the relationship ... 

Hydrobromic acid, a strong acid, completely ionizes in water. All of the A1(0H)3 that dissolves dissociates, so it is technically a strong base. However, because it is so insoluble, few OH ions are produced, and A1(0H)3 acts as a weak base. Therefore, the ionic equation shows little dissociation of the base. The dissociated salt, AlBr3, is also shown as ions. 

The data represented by dependence 4 (Fig. 2.4.9a) show that carbonate ions are incompletely dissociated according to equation (2.3), even in diluted solutions, since the corresponding calibration E-pO plot is located above the similar plot obtained with the use of strong bases (KOH or NaOH). The calibration -pO plot for the Pt(02)lYSZ electrode, obtained at 800 °C, has no appreciable distinction from the plots constructed at 700 °C it consists of two linear sections with the inflection point located at pO 3. The parameters of the calibration E-pO plots obtained in the molten KCl-NaCl eutectic melt are contained in Table 2.4.3. 

The above-mentioned considerations show that sodium peroxide cannot be considered a strong base at temperatures below 400 °C, even in an oxygen-free atmosphere because of incomplete dissociation according to equation (2.5.42). The practical impossibility of purifying this Lux base from carbonate ions imposes additional limitations on its use for oxoacidity studies in nonoxidizing melts and at relatively low experimental temperatures. 

The calculation of the pH of a mixture of a weak acid and a strong base is considered next, and is slightly more complicated. (The development of the equations for a weak base and a strong acid is left for the reader as Problem 15.5.) For simplicity of presentation, we will neglect the ionization of water, except at the neutral point (pH = 7) or when there is an excess of base, and also neglect solution nonidealities. Of course, electrolyte solution nonideality can be included following a procedure such as that in the illustration above. The dissociation reactions of a weak acid and a strong base are... 

These equations are based on an assumption of complete dissociation. If an electrolyte is neither a strong nor a weak electrolyte, these equations must be modified by a factor involving the degree of dissociation. For weak electrolytes the ions are generally so far apart that the ionic atmospheres are very diffuse the relaxation and electrophoretic... 

Hydrochloric acid is a strong acid, so all the HCl molecules dissociate to produce H" and Cr ions. Also, when the strong base NaOH dissolves, the solution contains Na" and OH ions. When these two solutions are mixed, the H ions from the hydrochloric acid react with the OH ions from the sodium hydroxide solution to form water. The balanced net ionic equation for the reaction is... 

Weak acids and weak bases do not ionize (or protolyze) completely in aqueous solution. The approach used to solve for the concentrations of solution components for weak acid or base solutions is similar to that used for strong acids and strong bases, but we are not able to make the simplifying assumption in theKa orKt, equilibrium equations that complete dissociation takes place. Typical calculations for weak acid and weak base systems are illustrated in the following example. 

Because HCl is a strong acid and NaOH is a strong base, their dissociation in aqueous solution is assumed to be complete. The equations needed to solve the problem are... 

Consider the net ionic equation for the reaction of a strong acid (HCl) and strong base (NaOH) in aqueous solution. In water, the acid H30 from the ionization of HCl and base OH from the dissociation of NaOH engage in Br0nsted-Lowry proton transfer to form H2O. The net ionic equation features the conjugate acid and base of water as reactants ... 

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