Water as a Solvent

In this experiment we will see how water can be a solvent. As you watch the video see which of the solutes are dissolved in the water.

Solvent - A liquid substance capable of dissolving other substances.

Solute - A substance that is dissolved in a solvent.

So what happened? First we need to understand that water is made of polar molecules.

Polar Molecule - A molecule that has a slight positive and negative charge due to an imbalance in the way electrons are shared.

Atoms are made from protons, neutrons, and electrons. Protons have a positive electrical charge, electrons have negative electrical charge, and neutrons have no electrical charge. Atoms form together by sharing their electrons, forming what is called a chemical bond.

When different kinds of atoms form together they become molecules. Polar Molecules are formed when one kind of atom is stronger then the other, and just like kids "sharing" a toy, whichever atom is stronger will end up with more electrons. In the case of water there are two hydrogen atom (H2) and 1 oxygen atom (O) per water molecule.

As it turns out, the oxygen atom is stronger then the hydrogen atoms, therefor the oxygen atom gets more of the electrons causing the oxygen atom to have a very slight negative charge, and the hydrogen atoms to have a slight positive charge. So water is made of polar molecules.

Polar molecules have a net electrical charge, and that charge wants to find other charges to interact with. There are two different categories of substances that contain an electrical charge. The first, as you know, is polar molecules. The second is ionic molecules.

When an atom loses or gains electrons, we say it has become an ion. And because of the imbalance of electrons, the ions have a net electrical charge. Ionic molecules are made up of ions. As an example, salt is made up of sodium ions, and chloride ions. You get sodium ions when a sodium atom loses an electron, and you get chloride ions when a chloride atom gains an electron.

When an ionic compound (something made from ionic molecules) is mixed with water, the electrical charges in the two substances attract each other. The water molecules surround the ions in the solute and pull them so far apart that the solute is no longer visible to the naked eye, but it is still there.

If you look at this picture you can see the water molecules separating the sodium ions, and the chloride ions. The positive charge in the hydrogen atoms is attracted to the negative charge of the chloride ions. And the negative charge in the oxygen atoms is attracted to the positive charge in the sodium ion. Pretty much the same thing happens when you dissolve a polar molecule in water. So water can disolve polar molecules, and ionic molecules. But as we saw in the expiriment, there are some things that water will not dissolve, namely non-polar molecules.

So if water, or other polar substances will not dissolve non-polar solutes, will anything? The answer is yes! Think about it... why can't water dissolve non-polar substances? Because non-polar substances have no electrical charge. So it stands to reason that non-polar solvents will dissolve non-polar solutes! For example, gasoline is a non-poler solvent. In our experiment we saw that sand and oil were non-polar solutes. So gasoline will potentially dissolve sand and oil!

How cool is that?

Well I hope you enjoyed my essay on Water as a Solvent. To learn more see Exploring Creation with Physical Science by Dr. Jay L. Wile, Module 4, pages 90-93. And next time you go to mix something in your water, think about whether or not it is a polar molecule or non-polar molecule!