Solubility of Substances in Water

Why was Priestley successful in preparing so many gases that had eluded those before him Remember from the first section of this chapter that only common air, carbon dioxide, and hydrogen were known before Priestley started his work. On the other hand, he was able to generate, collect, and characterize a number of gases (NH3, HCl, H2S, NO2, and SO2 among others) that, as it turned out, were soluble in water but insoluble in the liquid mercury that Priestley quite often used. This leads us to a consideration of the question of why water is such a good solvent for so many substances and how we can rationalize the solubility characteristics of various solutes in water. 

The general rule for predicting the solubility of various covalent solutes is the familiar like dissolves like. Polar solutes dissolve in polar solvents (like water) and nonpolar solutes dissolve in nonpolar solvents, but polar does not dissolve in nonpolar, and vice versa. Why is this (We had a hint of what is to come in the last chapter 

Oxygen (O2) and ammonia (NH3) molecules in water. A diagram showing (a) the relative insolubility of O2 molecules and (b) the solubility of NH3 molecules in liquid water. The O2 does not hydrogen-bond with water molecules, whereas the NH3 does. 

Some General Solubility Rules for Common Ionic Solutes in Water 

Group lA Li+,Na, K, Rb+, Cs, and ammonium = NHJ AH Group lA (alkali metal) and ammonium salts are soluble. 

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Many interrelated factors affect the solubility of substances in water. This makes it challenging to predict which ionic substances will dissolve in water. By performing experiments, chemists have developed guidelines to help them make predictions about solubility. In Investigation 9-A, you will perform your own experiments to develop quidelines about the solubility of ionic compounds in water. 

When the relative hydrophobicity of solutes is estimated by the partitioning in the solvent system, one is faced with the aforementioned problem arising when measuring the comparative solubility of substances in water and in an organic solvent, that is which solvent should be used to simulate a nonpolar medium. 

The solubility of substances in water is given in different terms, usually as g or mg of substance per 100 g or 1 litre of water. The dependence of the solubility of substances on temperature is expressed graphically by so-called solubility curves. Some of characteristic solubility curves are shown... 

In Fig. 3a, it is seen that the density of SCW is sensitive to both temperature and pressure around the critical point. As a result, the solubility of substances in water can easily be controlled by changing the density. 

Generally, they do not dissolve in water. However, water is an excellent solvent and can interact with and dissolve some covalent molecules better than others. Covalent substances are generally soluble in organic solvents. For a further discussion of solubility of substances in organic solvents see Chapters 14 and 15. 

A 0.750-g sample of solid benzoic acid, C7H6O2, was placed in a 0.500-L pressurized reaction vessel filled with 02 at 10.0 atm pressure and 25°C. The benzoic acid was burned completely to water and C02. What were the final mole fractions of C02 and H20 vapor in the resulting gas mixture brought to the initial temperature The vapor pressure of water at 25°C is 23.8 torr. Neglect both the volume occupied by nongaseous substances and the solubility of C02 in water. The water pressure in the gas phase cannot exceed the vapor pressure of water, so most of the water is condensed to the liquid. 

The Asp of hydroxyapatite, Ca5(P04)30H, is 6.8 X 10-37. Calculate the solubility of hydroxyapatite in pure water in moles per liter. How is the solubility of hydroxyapatite affected by adding acid When hydroxyapatite is treated with fluoride, the mineral fluorapatite, Ca5(P04)3F, forms. The Asp of this substance is 1 X 10 60. Calculate the solubility of fluorapatite in water. How do these calculations provide a rationale for the fluoridation of drinking water ... 

The basis for the relationship between bioconcentration and log Kow is the analogy for the partition process between the lipid phase of fish and water and the partition process between n-octanol and water. The reason for using K w arises from the ability of octanol to act as a satisfactory surrogate for lipids in fish tissue. Highly significant relationships between log Kow and the solubility of substances in cod liver oil and triolin exist (Niimi, 1991). Triolin is one of the most abundant triacylglycerols found in freshwater fish lipids (Henderson and Tocher, 1987). 

Solubility — The amount of a substance (solute) that will dissolve in a given amount of another substance (solvent). In terms of oil spill cleanup, it is most often the measure of how much oil will dissolve in the water column on a molecular basis. This is important in that the soluble fractions of the oil are sometimes toxic to aquatic life, especially at high concentrations. The solubility of oil in water is extremely low, generally less than 100 parts per million (ppm). (See also Dissolution.)... 

Chlorine, CI2, helps to keep swimming pools clean, but it has to be constandy either added to the water or formed in the water from other substances. With reference to the solubility of chlorine in water, explain why this is necessary. 

Increasing temperature usually iucreases the solubility of solid and liquid substances and decreases the solubility of gases in water. 

Figure 13.3 Like dissolves like solubility of methanol in water. The H bonds in water and in methanol are similar in type and strength, so they can substitute for one another. Thus, methanol is soluble in water in fact, the two substances are miscible.

A seven year smdy on the groundwater in the Paris region of France, revealed DEA was present at a concentration above that of its parent compound. The atrazine degradation pathway and the higher solubility of DEA in water may explain this finding. Recent work showed that photolysis of triazines and acetanilides followed pseudo first order kinetics, and the photodegradation in soils was accelerated as the content of organic matter increased. Another study showed that humic substances enhanced terbutylazine photolysis. ... 

Obtained results mean, that such srrrface-active substances carmot effectively inhibit the process of the mass transfer between the particles. Probably this is connected with a good solubility of emtrlsrfies in water. 

Nitromethane can form azeotrope with many organic solvents. Additionally, it can dissolve certain polymers, nitro compounds, and nitrate compounds. Nitromethane is partially miscible with water at 20 °C, the solubility of nitromethane in water is 9.5 % (by volume) or 10.5 % (by mass), meanwhile, the solubility of water in nitromethane is 1.75 % (by mass). Generally, the miscibility of nitromethane increases with the rise of temperature. Dry nitromethane is a neutral substance, thus it possesses excellent storage stabihty. After being stored for certain period of time, wet nitromethane will become acidic, which making it capable of corroding metals, however, adding a small amount of phosphoric acid or phosphate can effectively inhibit corrosion. 

The term solubility describes the amount of one substance (solute) that will dissolve in a specified amount of another substance (solvent) under stated conditions. For example, 36.0 g of sodium chloride will dissolve in 100 g of water at 20°C. We say then that the solubility of NaCl in water is 36.0 g/100 g H2O at 20°C. Solubility is often used in a relative way. For instance, we say that a substance is very soluble, moderately soluble, slightly soluble, or insoluble. Although these terms do not accurately indicate how much solute will dissolve, they are frequently used to describe the solubility of a substance qualitatively. 

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