Why does NaCl dissolve in water?
Answer:
Because sodium chloride is soluble in water:
NaCl(s) + H2O(l) → Na+ (aq) + Cl-(aq)
However, the soloubility is limited - only so much can be dissolved in a defined volumn of water at a given temperature and pressure. The solubility of NaCl in water is determined by the balance of intermolecular forces between the H2O and NaCl and the resulting entropy change. The solubility of NaCl which ionizes in water is determined by the solubility product (Ksp) which is a constant at a given temperature.
Anything that is able to dissolve in water is soluble and salt (sodium chloride) is soluble so it dissolves in water.
NaCl or salt is a solvent, while water is a very good solute. When you put some NaCl in water and stir, the NaCl dissolves as its particles disperse or diffuse in the water evenly throughout due to the high solubility of water and also because NaCl is soluble in water.
You can also say that this happens because particles of water have spaces between them, and when we put NaCl in water and stir, the particles of NaCl diffuse and occupy the small spaces or gaps in between the particles of water and thus, NaCl dissolves.
Hope that helps.
When an ionic crystal such as NaCl is placed in water, a dissolving reaction will occur. Initially, the positive and negative ion are only attracted to each other. The water molecules are hydrogen bonded to each other. If the crystal is to dissolve, these bonds must be broken.
Negative chloride ions on the surface are attracted by neighboring positive sodium ions and by the partially positive hydrogen atom in the polar water molecule (See the graphic on the left).
Similarly, the positive sodium ions are attracted by both chloride ions and the partially negative oxygen atom in the polar water molecule.
A "tug-of-war" occurs for the positive and negative ions between the other ions in the crystal and the water molecules. Several water molecules are attracted to each of the ions.
Whether the crystal dissolves is determined by which attractive force is stronger. If the internal ionic forces in the crystal are the strongest, the crystal does not dissolve. This is the situation in reactions where precipitates form. If the attractions for the ions by the polar water molecules are the strongest, the crystal will dissolve. This is the situation in sodium chloride.
The question of a salt's solubility in water is actually a much more delicate balance than most people realize after taking a first year chemistry course. One answer said that it dissolves because it's soluble. That's just restating the same fact.
The sodium chloride crystalline lattice is held together by strong ionic bonds. You have to break these bonds, which takes energy. You get the energy back (more or less) by the strong interactions between the solvent (water) and the individual ions. Other answers have spoken of these interactions correctly.
The sodium chloride crystalline lattice is also highly ordered. The "entropy term" in the overall spontaneity equation is influenced, therefore, by whether the ordering of the solvent around the ions balances against that original crystalline order. The previous answer addressed the energetic (enthalpic) contribution, but neglected completely the entropic contribution to overall reaction spontaneity.
When you look at different salts, you'll see some dissolve exothermically, others endothermically, some easily, and others not at all. So the truth is that the enthalpic and entropic terms of salts dissolving in a solvent (especially water) are often in quite delicate balance. That explains why temperature has such a profound effect on solubility in many cases. (T delta S).
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