Weak acids soluble salts

Figure 6.4 Solubility-pH profile of a weak acid, with salt precipitation taken into account. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

The solution of a salt derived from a strong base and weak acid is basic because the anion of a weak acid reacts with water (hydrolysis) to form hydroxide ions. Consider the soluble salt NaCIO found in chlorine bleaches prepared by reacting NaOH, a strong base, and HC10, a weak acid. The salt dissociates completely in water and the conjugate base of the weak acid, CIO-, hydrolyzes, producing OH- ions. 

The general rule is that if the anion X- is an effective base—that is, if HX is a weak acid—the salt MX will show increased solubility in an acidic solution. Examples of common anions that are effective bases are OH-, S2-, CO32-, C2042-, and Cr042-. Salts involving these anions are much more soluble in an acidic solution than in pure water. 

Saccharin, acting as a weak acid, forms salts with basic active pharmaceutical ingredients and these salts have the desirable property of enhanced water solubility <2005CG1073>. 

Strong adds Weak acids Strong bases Insoluble bases Weak bases Soluble salts Insoluble salts... 

Zone-B Solubility of the Weak Acid audits Salt Under Equilibrium Conditions Inside of the pH region enclosed by the limits of Zone-B, one hnds both the free acid and its salt form. The mass balance relationship in this zone defines the total solubility (Sj) at any particular pH value as the sum of the concentration of the free acid plus the concentration of its salt form ... 

Analytical Characters.—(1.) Hydrogen sulfid, in acid solution a black ppt. insoluble in alkaline sulfids, and in cold, dilute acids. (2.) Ammonium sulfhydrate black ppt. insoluble in excess. (3.) Hydrochloric acid white ppt. in not too dilute solution soluble in boiling HaO. (4.) Aiumoniuiu hy-droxid white ppt. insoluble in excess. (5.) Potash white ppt. soluble in excess, especially when heated. (6.) Sulfuric acid white ppt. insoluble in weak acids, soluble in solution of ammonium tartrate. (7.) Potassium iodid yellow ppt. sparingly soluble in boiling HaO soluble in large excess. (8.) Potassium chromate yellow ppt. soluble in KHO solution. (9.) Iron or zinc separate the element from solution of its salts. 

It has been stated that phenols are weak acids, and that their acidic property probably results from the fact that the aryl group which they contain is negative. The negative nature of the phenyl group is not highly developed, and, as a consequence, phenol is a very weak acid its salts are decomposed by carbonic acid. The extent to which acetic acid, carbonic acid, and phenol dissociate in one-tenth normal solution is 1.3, 0.174, and 0.0037 per cent, respectively, whereas at this concentration hydrochloric acid is dissociated to the extent of over 90 per cent. Notwithstanding the fact that phenols are such weak acids, they dissolve readily in alkalies. As they are weaker than carbonic acid, they are not soluble in carbonates. This fact is made use of in the separation of acids from phenols. 

You have two salts, AgX and AgY with very similar values. You know that HX is a strong acid and HY is a weak acid. Which salt is more soluble in an acidic solution Explain. 

Salt whose anion is conjugate base of weak acid Solubility increases as pH decreases... 

The activity coefflcients of the undissociated portions of the weak acids were calculated in the following manner using data presented by numerous authors of the solubility of the weak acid in salt solutions of varying concentrations ... 

The solution will then contain the free acid and the hydrochloride of the base either of these may separate if sparingly soluble. If a sohd crystallises from the cold solution, filter, test with sodium bicarbonate solution compare Section 111,85, (i) and compare the m.p. with that of the original compound. If it is a hydrolysis product, examine it separately. Otherwise, render the filtrate alkahne with sodium hydroxide solution and extract the base with ether if the presence of the unchanged acyl canpound is suspected, extract the base with weak acid. Identify the base in the usual manner (see Section IV, 100). The acid will be present as the sodium salt in the alkaline extract and may be identified as described in Section IV,175. 

Group II. The classes 1 to 5 are usually soluble in dilute alkali and acid. Useful information may, however, be obtained by examining the behaviour of Sails to alkaline or acidic solvents. With a salt of a water-soluble base, the characteristic odour of an amine is usually apparent when it is treated with dilute alkali likewise, the salt of a water soluble, weak acid is decomposed by dilute hydrochloric acid or by concentrated sulphuric acid. The water-soluble salt of a water-insoluble acid or base will give a precipitate of either the free acid or the free base when treated with dilute acid or dilute alkali. The salts of sulphonic acids and of quaternary bases (R4NOH) are unaflFected by dilute sodium hydroxide or hydrochloric acid. 

Iron Reduction. The reduction of nitrophenols with iron filings or turnings takes place in weakly acidic solution or suspension (30). The aminophenol formed is converted to the water soluble sodium aminopheno1 ate by adding sodium hydroxide before the iron-iron oxide sludge is separated from the reaction mixture (31). Adjustment of the solution pH leads to the precipitation of aminophenols, a procedure performed in the absence of air because the salts are very susceptible to oxidation in aqueous solution. 

Activators. Activators are chemicals that increase the rate of vulcanization by reacting first with the accelerators to form mbber soluble complexes. These complexes then react with the sulfur to achieve vulcanization. The most common activators are combinations of zinc oxide and stearic acid. Other metal oxides have been used for specific purposes, ie, lead, cadmium, etc, and other fatty acids used include lauric, oleic, and propionic acids. Soluble zinc salts of fatty acid such as zinc 2-ethyIhexanoate are also used, and these mbber-soluble activators are effective in natural mbber to produce low set, low creep compounds used in load-bearing appHcations. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. 

The characteristics of soluble sihcates relevant to various uses include the pH behavior of solutions, the rate of water loss from films, and dried film strength. The pH values of sihcate solutions are a function of composition and concentration. These solutions are alkaline, being composed of a salt of a strong base and a weak acid. The solutions exhibit up to twice the buffering action of other alkaline chemicals, eg, phosphate. An approximately linear empirical relationship exists between the modulus of sodium sihcate and the maximum solution pH for ratios of 2.0 to 4.0. 

The most common method of purification of inorganic species is by recrystallisation, usually from water. However, especially with salts of weak acids or of cations other than the alkaline and alkaline earth metals, care must be taken to minimise the effect of hydrolysis. This can be achieved, for example, by recrystallising acetates in the presence of dilute acetic acid. Nevertheless, there are many inorganic chemicals that are too insoluble or are hydrolysed by water so that no general purification method can be given. It is convenient that many inorganic substances have large temperature coefficients for their solubility in water, but in other cases recrystallisation is still possible by partial solvent evaporation. 

In seawater, HCO3 ions lead to surface films and increased polarization. In aqueous solutions low in salt and with low loading of the anodes, less easily soluble basic zinc chloride [10] and other basic salts of low solubility are formed. In impure waters, phosphates can also be present and can form ZnNH4P04, which is very insoluble [11]. These compounds are only precipitated in a relatively narrow range around pH 7. In weakly acid media due to hydrolysis at the working anode, the solubility increases considerably and the anode remains active, particularly in flowing and salt-rich media. 

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

For sparingly soluble salts of a strong acid the effect of the addition of an acid will be similar to that of any other indifferent electrolyte but if the sparingly soluble salt MA is the salt of a weak acid HA, then acids will, in general, have a solvent effect upon it. If hydrochloric acid is added to an aqueous suspension of such a salt, the following equilibrium will be established ... 

With the salts of certain weak acids, such as carbonic, sulphurous, and nitrous acids, an additional factor contributing to the increased solubility is the actual disappearance of the acid from solution either spontaneously, or on gentle warming. An explanation is thus provided for the well-known solubility of the sparingly soluble sulphites, carbonates, oxalates, phosphates(V), arsenites(III), arsenates(V), cyanides (with the exception of silver cyanide, which is actually a salt of the strong acid H[Ag(CN)2]), fluorides, acetates, and salts of other organic acids in strong acids. 

Solutions which prevent the hydrolysis of salts of weak acids and bases. If the precipitate is a salt of weak acid and is slightly soluble it may exhibit a tendency to hydrolyse, and the soluble product of hydrolysis will be a base the wash liquid must therefore be basic. Thus Mg(NH4)P04 may hydrolyse appreciably to give the hydrogenphosphate ion HPO and hydroxide ion, and should accordingly be washed with dilute aqueous ammonia. If salts of weak bases, such as hydrated iron(III), chromium(III), or aluminium ion, are to be separated from a precipitate, e.g. silica, by washing with water, the salts may be hydrolysed and their insoluble basic salts or hydroxides may be produced together with an acid ... 

Because the concentrations of ions in a solution of a sparingly soluble salt are low, we assume, just as we did for solutions of weak acids and bases (Section 10.7), that we can approximate Ksp by... 

Before leaving the subject of polarity and in relation to uptake and distribution, mention should be made of weak acids and bases. The complicating factor here is that they exist in solution in different forms, the balance between which is dependent on pH. The different forms have different polarities, and thus different values. In other words, the values measured are pH-dependent. Take, for example, the plant growth regulator herbicide 2,4-D. This is often formulated as the sodium or potassium salt, which has high water solubility. When dissolved in water, however, the following equilibrium is established ... 

C16-0105. Write the equilibrium reaction and equilibrium constant expression for each of the following processes (a) Trimethylamine, (CH3)3 N, a weak base, is added to water, (b) Hydrofluoric acid, HF, a weak acid, is added to water, (c) Solid calcium sulfate, CaSOq, a sparingly soluble salt, is added to water. 

An aqueous solution of a soluble salt contains cations and anions. These ions often have acid-base properties. Anions that are conjugate bases of weak acids make a solution basic. For example, sodium fluoride dissolves in water to give Na, F, and H2 O as major species. The fluoride anion is the conjugate base of the weak acid HF. This anion establishes a proton transfer equilibrium with water ... 

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