Explanation: According to the principle of similarity dissolution, water is a more polar solvent, and ethyl acetate is a less polar solvent, so the solubility of mutual dissolution is low. When inorganic salts are added, the polarity of the aqueous phase is further increased, so ethyl acetate is more difficult to dissolve in water.
Therefore, please consider for yourself the similarities and differences between this phenomenon and the following:
These phenomena are all more or less different, but in fact they can all be explained by a unified theory. Discussions are welcome.
Sort it out as follows:
These phenomena can be explained more intuitively at the microscopic level:
The dissolution of a substance in a solvent is usually accompanied by a solvation process, i.e. the interaction between the solvent and the solute particles.
We can regard the dissolution of ethyl acetate as a process of hydration, and the dissolution of ethyl acetate forms a solvated structure, which is expressed here as CH3COOEt 🥰 nH2O:
CH3COOEt (l) + nH2O (l) → CH3COOEt ▽ nH2O (aq)
And when sodium and chloride ions dissolve, they also form a hydrated structure (for convenience of description, use NaCl as an example):
NaCl (s) + (x + y) H2O (l) → Na + 🥰 xH2O (aq) + Cl − 🥰 yH2O (aq)
It is important to note that water is a polar molecule that can bind chloride and sodium ions through the positive (hydrogen) and negative (oxygen) terminals, respectively. This charge-dipole interaction (or Cl · H-O hydrogen bonding) is relatively strong, the equilibrium constant [1] is large, and the number of water molecules that ions can attract is also large (i.e. x, y is large).
However, for ethyl acetate with very small polarity, it binds to water molecules mainly in a relatively weaker interaction of dipole-dipole (or induced dipole), and its equilibrium constant is much lower than that of inorganic ions, and the number of bound water molecules n is also very small.
[1] For this type of hydration reaction, the number of water molecules bound by the solute is uncertain, and the original solute molecule (water) needs to be regarded as the reactant, so the "equilibrium constant" is usually not used to describe it. This concept is only used here to indicate the difficulty of the reaction.
So, we can think of this process simply as a shift in equilibrium. Ethyl acetate and inorganic salts are both substances that can bind to water molecules, and ions that bind more strongly to water molecules "snatch" the water molecules that were originally weakly bound to ethyl acetate, making ethyl acetate less susceptible to solvation by water molecules, making it more difficult to dissolve in water.
Repeat this sentence again:
The dissolution of a substance in a solvent is usually accompanied by a solvation process, i.e. the interaction between the solvent and the solute particles.
Then let's take a look at the previous phenomena:
@Sodium chloride solution can promote the separation of aqueous and organic phases.
One of the reasons for this phenomenon is the reduced solubility; and the more important reason is the phenomenon of "demulsification": that is, the tiny droplets formed by organic solvents form a metastable heterogeneous state (ie emulsification) in water, and the addition of excess salts to the solution will destroy the emulsification and accelerate the convergence of small droplets.
This can also be explained by the above-mentioned principle of equilibrium: emulsification can be regarded as a generalized "dissolution" [2], which can be understood as each organic droplet as a large "molecule". This droplet also needs to attract a layer of water molecules to stabilize, and the addition of inorganic salts will cause the droplet to lose most of the surrounding water molecules, making it impossible to exist stably in water, combine with each other to form large droplets, and merge into the organic phase layer under the action of unbalanced gravity and buoyancy.
Summary: Inorganic ions "snatch" the water molecules around the droplet, promoting liquid separation.
[2] Note: This is just a way of understanding. By definition, solutions are generally considered to be homogeneous systems.
@Protein solution can be reversibly precipitated by adding more inorganic salts.
Inorganic ions "snatch" the water molecules around the protein, undermining the stability of the protein colloid.
@The addition of ethanol to saturated copper sulfate solution can precipitate (hydrate) copper sulfate solids.
The combination of ethanol and water is relatively stable, and can even be miscible in any ratio. Therefore, ethanol "robs" the water in the hydrated inorganic ions, causing copper sulfate to precipitate (and therefore, the water content in the precipitated crystals will be reduced, and copper sulfate monohydrate may be obtained).
@Sodium chloride can reduce the solubility of chlorine in water
A common saying is:
Due to the existence of the following two balances,
Cl2 (g) Cl2 (aq); Cl2 (aq) + H2O (l) H + (aq) + Cl − (aq) + HClO (aq)
In saturated sodium chloride solution, the second reaction product is inhibited by chloride ions, and the equilibrium shifts to the left, causing the equilibrium of the first reaction to shift to the left, reducing the solubility of chlorine gas.
Personally, I think this statement is not rigorous: in a neutral solution, the ionization degree of chlorine is far less than 50% when the second reaction reaches equilibrium, and even if the ionization part is completely suppressed, it will not cause a significant change in the solubility of chlorine.
In fact, chlorine dissolves in water by various interactions with water molecules. Chloride ions compete with chlorine molecules to bind water molecules, thus reducing the solubility of chlorine gas.
To clarify, the above is mainly to help understand the relevant knowledge. If you pass the high school test, please write "same ion effect", OK?
@Adding sodium hydroxide solution to ammonia water will release ammonia
The same is true, the ionization degree of ammonia is not high, and hydroxide can inhibit ammonia dissolution because hydroxide can compete with ammonia molecules to bind water molecules.
H3N... H − OH + OH − HO −... H − OH + NH3
In short, chemical knowledge also focuses on understanding, and many phenomena can be understood using a system, which means "always change".
