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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5 Key excerpts on "Solubility Curve"
eBook - ePubChemical Process Equipment
Selection and Design
- James R. Couper, W Roy Penney, James R. Fair PhD, 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 - PDFEtching of Crystals
Theory, Experiment and Application
- K. Sangwal(Author)
- 2012(Publication Date)
- North Holland(Publisher)
Consequently, the factor (β'μ - β as a rule, has a negative value and the solubility of a salt decreases with a decrease in ε (fig. 6.3). 6.4. Temperature dependence of the solubility The solubility of the majority of substances increases with an increase in temperature, but there are also substances for which the solubility increases 206 Solubility of crystals and complexes in solution [§6.4 0 2 3 4 5 6 7 8 2 4 ο ο cn ο 6 8 10 J 1 J_ 2 4 6 8 1 0 3 / ( f 0 10 Fig. 6.3. Dependence of the logarithm of the solubility of CsCl (curves 1, 2) and AgCl salts (curves 3,4) on the inverse of the dielectric constant of water; curves 1, 3 are for alcohols, and curves 2, 4 for ketones. The figures on the upper horizontal axis denote the solvents: (1) water, (2) methanol, (3) ethanol, (4) acetone, (5) methylethylketone, (6) butanol, (7) amyl alcohol, and (8) methylpropyl ketone. (After Izmailov 1976.) only very slightly or even decreases. For some substances the Solubility Curve exhibits a discontinuity, which denotes a phase change. The Solubility Curves for two different phases of a salt meet at the transition point, and salts such as ferrous sulphate show a number of these points. Below the transition point the solubility of a substance may increase, while above this point it may decrease with an increase in temperature, or vice versa. A majority of solutes dissolve in their near-saturated solutions with an absorption of heat (i.e. the heat of solution, AH S , is negative), which increases the temperature of these solutions, thus resulting in an increase in their solubility with temperature. These solutes are said to exhibit a positive temperature-coefficient of solubility. Some solutes dissolve in their near-saturated solutions with the liberation of heat (i.e. AH S is positive), which decreases their tempera-ture, thus decreasing their solubility with an increase in temperature. These substances are said to exhibit a negative temperature-coefficient of solubility. These trends of the Solubility Curve follow from Le Chatelier's principle, which states that when a system in equilibrium is subjected to a change in temperature or pressure, the system adjusts itself to a new equilibrium state in order to relieve
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 - PDF- Allan S. Myerson, Deniz Erdemir, Alfred Y. Lee(Authors)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
It is assumed that the tem- perature at which the last crystal disappears is the solubility temperature at the concentration of solution (total solute added per solvent in system). This is again incorrect because dissolution is not an instantaneous process and, in fact, becomes quite slow as the saturation temperature is approached. This method will underestimate the solubility because the solution will have been heated above the saturation temperature. Instead, slow heating rates should be used to for non-isothermal solubility measurements. If slow dissolution kinetics are a concern, one can increase the temperature of the solution by 1°C every 30–40 minutes until full dissolution is reached, resulting in Solubility Curves that are generally accurate within 5 percent (Yi et al. 2005). Regardless, it is important to note that the accuracy of non-isothermal solubi- lity measurements is a function of hold time between tempera- ture ramp steps and the ramp step size. Accurate solubility data are worth the time and trouble it will take to do the experiment correctly. Avoid the common errors discussed, and be suspicious of data where the techni- ques used in measurement are not known. 1.5 Supersaturation and Metastability As we saw in Section 1.4, solubility provides the concentration at which the solid solute and the liquid solution are at equilibrium. This is important because it allows calculation of the maximum yield of product crystals accompanying a change of state from one concentration to another in which crystals form. For exam- ple, if we look at Figure 1.15, which gives us the solubility diagram for KCl, if we start with 1000 kg of a solution at 100° C and a concentration of 567 g/kg of water and cool it to 10°C at equilibrium, we will have 836 kg of solution with a KCl con- centration of 310 g/kg of water and 164 kg of solid KCl.
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
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