Chemistry
Solubility Curve
A solubility curve is a graphical representation of the solubility of a substance in a solvent at a given temperature. It shows the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. The curve can be used to determine the saturation point of a solution.
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6 Key excerpts on "Solubility Curve"
eBook - ePubChemical Process Equipment
Selection and Design
- James R. Couper, W Roy Penney, James R. Fair PhD(Authors)
- 2012(Publication Date)
- Butterworth-Heinemann(Publisher)
T s between the heating media and the slurry. Sodium sulfate and sodium carbonate monohydrate exhibit this type of solubility.Curve 4
Curve 4 exhibits very steep solubility. Yield is obtained by cooling the feed solution. To prevent fines formation, the cooling must exactly follow the Solubility Curve. This is done automatically in batch crystallizers. Continuous crystallizers in series must have the crystallizer stage temperatures selected so as not to cross the Solubility Curve. Benzoic acid and DMT exhibit this type of solubility.16.3 Solubilities and Equilibria
The variation of the solubilities of most substances with temperature is fairly regular, and usually increases with temperature. When water is the solvent, breaks may occur in Solubility Curves because of the formation of hydrates. Figure 16.2(a) shows such breaks, and they can be also discerned in Figures 16.2(b) and (c) . Unbroken lines usually are well enough represented by second degree polynomials in temperature, but the Clapeyron-type equation with only two constants, ln is of good accuracy, as appears for some cases on Figure 16.2(b) .Figure 16.2 Solubility relations. (a) Linear plot of solubilities against temperature (Mullin, 1972 ). (b) Solubility against temperature plotted according to the equation (Mullin, 1972 ). (c) Normal and supersolubilities of two salts (data collected by Khamskii, 1969 ). (d) Identification of regions on solubility plots. In the unstable region, nucleation and growth are spontaneous. In the metastable region growth can occur on externally introduced particles. Along a – d to the left or along upwards, nucleation and growth can start at c or c ′, but a substantial nuclei growth rate will not be achieved until d or d ′ are reached.A convenient unit of solubility is the mass of solute per unit mass of solvent, or commonly g solute/100 g solvent. Interconversions with molal units and mol fractions are made readily when densities of the solutions are known.
eBook - ePubGeneral Physics
Mechanics and Molecular Physics
- L D Landau(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
Solutions are mixtures of two or more substances in which the substances are mixed on the molecular scale. The relative amounts of the various substances in the mixture may vary over a more or less wide range. If one substance is present in greater quantity than the others, it is called the solvent and the other substances are called solutes. The composition of a solution is described by its concentration that gives the relation between the quantities of the substances in the mixture —the components of the mixture as they are called. The concentration can be defined in various ways. Physically, the most informative is the molar concentration, that is, the ratio of the numbers of molecules or the ratio of the quantities expressed in moles. Alternatively, one may use concentrations by weight, volume, and so on. The mutual solubility of two substances usually has definite limits; no more than a certain amount of solute can dissolve in a given quantity of solvent. A solution containing the maximum possible quantity of solute is said to be saturated. If further solute is added to such a solution, it will not dissolve. Therefore, it can be said that a saturated solution is one that is in thermal equilibrium with the pure solute. The concentration of the saturated solution is a measure of the ability of a given substance to dissolve in the solvent concerned and is simply called the solubility of the substance. The solubility in general depends on the temperature.§77. Solubility
Solutions are mixtures of two or more substances in which the substances are mixed on the molecular scale. The relative amounts of the various substances in the mixture may vary over a more or less wide range. If one substance is present in greater quantity than the others, it is called the solvent , and the other substances are called solutes .The composition of a solution is described by its concentration , which gives the relation between the quantities of the substances in the mixture – the components of the mixture, as they are called. The concentration can be defined in various ways. Physically, the most informative is the molar concentration, i.e. the ratio of the numbers of molecules (or, what is the same thing, the ratio of the quantities expressed in moles). Alternatively, we may use concentrations by weight, by volume (the volume of substance dissolved in a given volume of solvent), and so on.The process of dissolution is accompanied by the evolution or absorption of heat. The quantity of heat depends not only on the quantity of solute but also on the quantity of solvent.The heat of solution is usually defined as the quantity of heat evolved or absorbed in the dissolution of one gram-molecule of substance in a quantity of solvent so large that any further dilution would cause no thermal effect. For example, the heat of solution of sulphuric acid (H2 SO4 ) in water is +75 000 J (the plus sign denoting that heat is evolved); the heat of solution of ammonium chloride (NH4 C1) is − 16 500 J (the minus sign shows that heat is absorbed).The mutual solubility of two substances usually has definite limits: no more than a certain amount of solute can dissolve in a given quantity of solvent. A solution containing the maximum possible quantity of solute is said to be saturated
eBook - ePub- Christoph Saal, Anita Nair, Christoph Saal, Anita Nair(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
A change in solid-state form in the range of temperatures covered is accompanied by a change in slope of the Solubility Curve. The change in slope between solvates or between a solvate and an ansolvate is usually quite high, with the solid-state form of the higher solvated form having the lower heat of dissolution and consequently a lower slope.- In enantiotropic systems, there is only one crossing between the forms.
- If a change in solid-state form occurs and if at least one of the solid-state residues is a solvate, the degree of solvatization decreases with increasing temperature.
Solubility isotherms as a function of solvent composition Linear plot Curves can be either concave, convex, or even exhibit a maximum. Plot log of concentration as a function of solvent composition- For a solubility isotherm, a change of the solid-state form of the solid residue can only concern a change in the degree of solvatization or in the solvent of solvatization.
- The higher the concentration of the solvent of solvatization, the more stable is the respective solvate and the higher is the degree of solvatization with this solvent.
- Plot solubility isotherms reduced with the solubility in pure primary solvent
Plotting the data according to the suggestions in Table 10.3, that is, in a manner that the data points form a straight line and making some good practice judgement can help improve the quality of the solubility measurements drastically.Some few rules apply to the transition points between polymorphs and between differently solvated forms. These should also be used for a plausibility check of the data (Table 10.4 ). However, there are also exceptions from these rules, like hydrates that convert to anhydrates in aqueous suspensions [20
eBook - ePub- Simon Gaisford, Mark Saunders(Authors)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
4.5 ) the reason for the term equilibrium solubility noted earlier.It appears from Equation (4.2 ) that the crystal lattice energy might affect solubility. It also seems from Equation (4.1 ) that there should be an effect of temperature on solubility, since the position of equilibrium will change. Both of these effects can be explored further through the concept of ideal solubility .Summary box 4.14.2.1 Ideal solubility- Solubility is the maximum concentration of a given solute that can be attained in a given solvent.
- Solids transition to solution by dissolution.
- Thermodynamic solubility is a position of equilibrium.
- Dissolution governs the rate at which solubility is achieved.
- As a general rule, solubility below 1 mg mL−1 is likely to hinder development while solubility above 10 mg mL−1 is acceptable.
In the special case where the enthalpy of any solute–solvent interaction is equal to the enthalpy of any solvent–solvent interaction then solvation of the solute may occur with no change in enthalpy (i.e. Δmix H = 0) and dissolution is said to be ideal . Formation of an ideal solution also occurs with the following change in entropy ( ):(4.6)where R is the universal gas constant (8.314 J K−1 mol−1 ). Ideal dissolution (although unlikely, because the solute and solvent molecules would need to possess identical properties, such as size, shape and chemical nature) leads to ideal solubility and is an interesting theoretical position because it can be described in thermodynamic terms, which allows calculation of the dependence of solubility on temperature.From Equation (4.2 ) if Δmix H = 0 then Δf H is equal to Δsol H (note that since Δf H must be positive, i.e. endothermic, Δsol H must also be positive for ideal dissolution). For a process to occur spontaneously the Gibbs free energy (ΔG ) must be negative. The familiar thermodynamic relationship for dissolution is(4.7)where T is absolute temperature. Δsol G is most likely to be negative when Δsol H is negative but, as noted above, Δsol H is frequently positive for dissolution and must be so when dissolution is ideal. This means that for dissolution to occur spontaneously the driving force can only be a significant increase in entropy. Since the mole fractions of both solvent and solute must be less than 1, the logarithmic terms in Equation (4.6
eBook - ePub- Christianto Wibowo, Ka Ming Ng(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
2 Basics of Solid–Liquid Equilibrium Phase Behavior2.1 Solid–Liquid Equilibrium
Solid–liquid equilibrium (SLE) provides the thermodynamic basis for the design and synthesis of crystallization processes. Therefore, before delving into the subject of conceptual design of crystallization processes, it is imperative to understand the basics of SLE phase behavior and its representation using phase diagrams.2.1.1 Melting point and solubility
For a single-component system, SLE simply involves equilibrium at the pure component melting point (or freezing point). For example, water and ice are in equilibrium at 0 °C and 1 atm. The SLE of a binary system usually involves the solubility of one component (solute) in the other (solvent). For many systems, solubility varies significantly with temperature, such as that of sugar in water. The dependence of solubility on temperature is often plotted as the Solubility Curve, as illustrated in Figure 2.1a for sucrose in water. It is well known that solubility behavior may not be always that simple, with the potential presence of hydrates, solvates, or different polymorphic forms. There can be multiple Solubility Curves corresponding to the different forms of the solute.Figure 2.1: Examples of SLE relationships of binary systems: (a) sucrose solubility in water (data from [32 ]), and (b) freezing point depression in NaCl solution in water (data from [33 ]).The freezing point of the solution is affected by solute concentration, a phenomenon commonly referred to as freezing point depression. A simple example is the use of salt to melt snow in the winter by lowering the freezing point of water to below the ambient temperature. As shown in Figure 2.1b
eBook - ePubEnvironmental Engineering
Principles and Practice
- Richard O. Mines(Author)
- 2014(Publication Date)
- Wiley-Blackwell(Publisher)
2.7 Solubility (solubility product) So far, we have dealt with aqueous solutions in which the chemical species are highly soluble. In this section, our focus will be on liquid-solid species that are partially soluble or insoluble. All solids, no matter how seemingly insoluble, are soluble to some degree. When a solid is placed in water, the ions at the surface of the solid will migrate into the water. This is called dissolution. Simultaneously, ions in the solution will be redeposited on the surface of the solid; this is known as precipitation. Equilibrium will be reached between the crystals of the compound in the solid state and its ions in solution. In general, the solubility of most compounds increases with increasing temperature. Snoeyink & Jenkins (1980, page 251) indicate that the solubilities of and do not increase as temperature increases. Equation (2.112) shows the general equation of a solid compound dissolving in pure water to form its constituent ions. 2.112 The equilibrium expression is written as follows: 2.113 As described by Sawyer & McCarty (1994, page 37), at equilibrium or saturation, the surface area of the solid is the only portion that is in equilibrium with the ions in solution. Therefore, the concentration of solid as represented by in the denominator of Equation (2.113) can be considered a constant in equilibrium solubility problems. Equation (2.114) is rewritten to show the development of the solubility-product constant, 2.114 2.115 When the solution is saturated or at equilibrium. When the solution is under-saturated and no solids species are present. When the solution is super-saturated and solid species are being formed. The solubility-product constants for several solids of significance in environmental engineering are presented in Table 2.16. Partially soluble salts have small values, while soluble salts have relatively large values
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