In crudest terms it is the molecule in the mixture with the highest concentration. That is to say if you had a liter of salt and 2 grams of water. In that case, the salt would be the solvent and the water the solute.
But this type of mixture would be useless so why bother to make it??? When we do place solutes and solvents together, there is what we call the solution process. You can think of it as being similar to what you would experience if you tried to squeeze into an already packed elevator.
Everyone has to adjust to "find their space" again. Now just like in the elevator, molecules will adjust differently dependent on the type of molecule making an entrance. And also like in an elevator there will come a point when no more people can be added. For a solution, this point is called the saturation point and the solution itself is called a saturated solution.
At the point of saturation, no more solute will dissolve in the solvent. Rather the process of dissolving and precipitation are both occurring simultaneously and at the same rate. Generally speaking only certain molecules will dissolve in water to begin with.
The old phrase "like dissolves like" or "birds of a feather flock together" is very true with respect to what degree solutes are soluble or miscible in different solvents. At very low concentrations, almost all molecules are somewhat soluble in all solvents.
But by trend, ionic and polar solutes are more soluble in polar solvents and non-polar molecules are soluble in non-polar mostly organic solvents.
The units of concentration we just discussed are used to describe the degree to which a solute is soluble in a solvent. When you place a non-polar molecule in a polar solvent like oil in water the molecules try to minimize surface contact between them. This is actually the basis for the cells in our bodies. The lipids oily fatty acids form our cell membranes so that their non-polar tails face inward away from the polar cytoplasm and the polar heads face towards the polar cytoplasm.
Although much of the explanation for why certain substances mix and form solutions and why others do not is beyond the scope of this class, we can get a glimpse at why solutions form by taking a look at the process by which ethanol, C 2 H 5 OH, dissolves in water.
Ethanol is actually miscible in water, which means that the two liquids can be mixed in any proportion without any limit to their solubility. Much of what we now know about the tendency of particles to become more dispersed can be used to understand this kind of change as well. Picture a layer of ethanol being carefully added to the top of some water Figure below.
With covalent bonds, they have to share them. Now think about a magnet. So do batteries. So does the Earth. When things are different at each end, we call them polar. Some molecules have positive and negative ends too, and when they do, we call them polar. If they don't, we call them non-polar. Things that are polar can attract and repel each other opposite charges attract, alike charges repel.
The two magnets in the image above will attract because their opposite poles are near. Reverse one of them and they will repel each other. So why do soaps and detergents clean our dishes and our clothes? Soaps are chemically similar to cell membranes. Polar solvents Water is the most common polar solvent on Earth.
It will dissolve acids, ionic salts, alcohol, ammonia, sugars and even silicates from rock if under high pressure and temperature. Non-polar solvents The most common non-polar solvents and solutes are the hydrocarbons. Mainly found in crude oils and tars, hydrocarbons, like petrol and mineral turpentine, will dissolve oils, grease, wax, tar, methane gas and most organic molecules. Like dissolves like Will all solvents dissolve all solutes?
Water dissolving salt. Non-polar dissolution. Oil in water. Used with Permission. Let's imagine what happens when a polar solute such as sodium chloride is placed in a nonpolar solvent such as carbon tetrachloride.
Because CCl 4 doesn't have a partial charge, it won't attach itself to the sodium or chloride ions. As we've mentioned before, the sodium and chloride ions in NaCl are strongly attracted to one another because of their opposite charges. This very weak solvent-solute interaction, as well as the very strong attraction between neighboring solute particles, causes sodium chloride to be insoluble in carbon tetrachloride.
If we place a nonpolar solid into a nonpolar liquid, "like dissolves like" implies that the solid will dissolve. However, the only forces that will cause the liquid to be attracted to the solid are weak London dispersion forces. Why should the solid dissolve? Let's imagine that we have placed a chunk of carbon tetrabromide in a beaker containing carbon tetrachloride. The carbon tetrabromide molecules in the solid are held together by very weak London dispersion forces, as are the carbon tetrachloride molecules in the solvent.
One might expect, then, that there is no particular reason for the solute to dissolve. As it turns out, there's another force involved. Processes that increase the randomness of a system usually occur spontaneously we'll discuss this phenomenon, known as entropy.
Because the molecules in carbon tetrabromide will be made more random if they're mixed with another compound, the carbon tetrabromide will dissolve in the carbon tetrachloride. All rights reserved including the right of reproduction in whole or in part in any form.
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