Question

Is there any other aspect that gets important when dissolving a solute in a liquid besides polarity? Answer in greater than 100 words please.

Answer 1

Solvent classifications

Solvents can be broadly classified into two categories: polar and non-polar.

H₂O, NH₃, CH₃OH, NO, CO, HCl, H₂S, PH₃ etc are called polar compounds.

Substances such as H₂, O₂, N₂, CH₄, CCl₄ etc are called non-polar compounds,

                       Like dissolves like.

Polar materials dissolve polar materials whereas non-polar materials will mix and become true solutions.

An additional factor to consider is the hydrogen bonding. For example, ethanol and water are completely miscible at any proportion due to the extensive hydrogen bonding among their molecules.

Electrolytes or ionic substances are soluble in water due to hydration.

Due to the strong polarity of the water molecule, the positive and negative ions are pushed apart. In general, reasonable size ions are believed to have six water molecules around them, but these water molecules readily exchange with those in the medium.

There are many applications of this rule. On the small scale, personal hygiene and household cleaning requires various types of cleaning agents.

Other factor such as temperature and pressure also affects the solubility of a solvent. Thus, in specifying solubility, one should be aware of the factors.

1.Generally, the Dielectric Constant of the solvent provides a rough measure of a solvent's polarity.

• Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar.
• The dielectric constant measures the solvent's tendency to partly cancel the field strength of the electric field of a particle immersed in it.
• Generally, the dielectric constant of a solvent is an acceptable predictor of the solvent's ability to dissolve common ionic compounds, such as salts.

2.Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong Lewis acid or a strong Lewis base.

3.The Hildebrand parameter is the square root of cohesive energy density. It can be used with nonpolar compounds, but cannot accommodate complex chemistry.

4.Reichardt's dye, a solvatochromic dye that changes color in response to polarity. E_T is the transition energy between the ground state and the lowest excited state in kcal/mol and identifies the dye. Another, roughly correlated scale (E_T(33)) can be defined with Nile red.

5.Polarity can be separated to different contributions. For example, the Kamlet-Taft parameters are dipolarity (π*), hydrogen-bonding acidity (α) and hydrogen-bonding basicity (β). These can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent, usually including Reichardt's dye, nitroaniline and diethylnitroaniline. Another option, Hansen's parameters, separates the cohesive energy density into dispersion, polar and hydrogen bonding contributions.

6.    Hansen solubility parameter values

The Hansen solubility parameter values are based on dispersion bonds (δD) and hydrogen bonds (δH). These contain information about the inter-molecular interactions with other solvents and also with polymers, pigments, nanoparticles, etc.

7.      The Hildebrand Solubility Parameter it is the total van der Waals force, however, which is reflected in the simplest solubility value the Hildebrand solubility parameter. The solubility parameter is a numerical value that indicates the relative solvency behavior of a specific solvent. It is derived from the cohesive energy density of the solvent, which in turn is derived from the heat of vaporization. What this means will be clarified when we understand the relationship between vaporization, van der Waals forces, and solubility.