Why is alcohol soluble in water

To be able to mix, the molecules of both liquids have to be able to attract one another. Molecules that are polar meaning their electric charge is distributed unevenly so they have a more positive side and a more negative side tend to form hydrogen bonds whereas nonpolar molecules which have an equal charge balance do not tend to form such bonds.

Because water molecules are polar, any liquid that does not have polar molecules—such as oil—is usually immiscible with water. Rubbing alcohol molecules have a polar and nonpolar part, which means they are able to form hydrogen bonds with water and therefore able to mix with it.

But how can you break these bonds in order to separate both liquids once they are mixed? You have to add something to the mixture that competes with the alcohol in binding to the water molecules. One substance that can do that is salt. Salt is an ionic compound, meaning it is a substance made up of electrically charged molecules called ions. When ionic compounds dissolve in water, the individual ions separate and get surrounded by water molecules—a process called solvation.

Because the salt ions are charged, they dissolve much better in a polar solvent, which is also slightly more charged than a nonpolar solvent. For this reason, salt ions attract the water molecules much more strongly than alcohol molecules do because alcohol is less polar than water.

This means that when there is a lot of salt, all the water molecules will bond to the salt ions, leaving none to form hydrogen bonds with the alcohol molecules. As a result, the alcohol becomes immiscible with water and starts to form a separate layer. Historically this method has been used in the soap-making process to remove ingredients that should not be in the final soap product. Salting out is also commonly used in biochemistry laboratories to purify proteins, because different protein molecules become immiscible at different concentrations of salt solutions.

Chemists use this technique to extract liquids out of a solution, which is what you are going to do in this activity: You will separate a rubbing alcohol and water mixture using just a teaspoon of table salt!

Observations and results You should have seen that the salt easily dissolved in the water in cup 1. After shaking it the salt seemed to disappear. Remember that this occurs because the ionic salt molecules easily bond to the polar water molecules. The salt, however, did not dissolve as easily in the rubbing alcohol in cup 2.

Even after shaking it you will still be able to see the salt. This occurs because the alcohol molecules are less polar than water is, so the salt ions do not bond with them as easily.

With the permanent marker ink you should have observed the exact opposite phenomenon. The ink does not dissolve well in water but it does easily in the alcohol, giving the latter much more color. This is due to the fact rubbing alcohol also has a portion of its molecule that has no charges, and is nonpolar. This portion is more compatible with nonpolar molecules such as the marker ink. The alcohol dissolves in the water to form a homogenous solution, so you cannot distinguish the alcohol and the water anymore.

If you add salt to the mixture, however, the salt wants to dissolve in the water and competes with the alcohol for the water molecules. Because there are fewer water molecules available to make hydrogen bonds with the alcohol molecules, the alcohol becomes less soluble in the water—alcohol mixture, eventually forming a separate layer on top of the water. Both layers should have a different color, with the water mostly clear and the alcohol more colored.

This occurs because the marker ink is more soluble in the rubbing alcohol. Cleanup Flush all your mixtures down the sink with plenty of cold water. Wash your hands and clean your work area. Jump to navigation. In case of alcohols, just as it happens in case of many other biological molecules, the basic solubility rule that like dissolves like is a bit more complexed.

Each alcohol consists of a carbon chain always nonpolar and a OH group which is polar. For ethanol for example the chemical formula looks lie this: C 2 H 5 OH. Dec 20, Isopropyl alcohol is soluble in water because it can form strong hydrogen bonds to the water. Explanation: The solubility of an alcohol in water is a competition between two parts of the molecule: the polar "OH" group and the nonpolar hydrocarbon portion.

So, isopropyl alcohol is soluble in water in all proportions. Related questions Question a. Why are organic compounds important? How are compounds in organic chemistry named?