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True or false? Water molecules have distinct positive and negative areas.


Michael wants to remove this oily stain from his t-shirt. But just using water won't do it. Why not? Because the oil molecules are nonpolar. They don't have any specific areas that are positive or negative.

While the water molecules do. They are polar, with a more positive side and a more negative side. To get rid of the stain, Michael needs to find a nonpolar solvent. There are some strong and smelly alternatives, like paint thinner and acetone, but he doesn't want to ruin the T-shirt. Fortunately, there's something we use everyday that works almost as well -- soap.

On one side of a soap molecule, there are two oxygen atoms. These oxygen atoms are negatively charged, so the whole molecule is - an ion. That means it can easily be dissolved in water. On the other side of the molecule, we find a long "tail" of carbon and hydrogen atoms. There are no positive nor negative areas in the tail, so this part of the soap molecule is nonpolar.

That means it is good at dissolving other nonpolar substances, such as fat. Since like dissolves like, one end of the soap molecule can dissolve oil and fat - and the other end can get dissolved in water. When Michael applies the soap to the stain, the nonpolar tails envelop the grease. When he rinses with water, the polar ends of the soap molecules will point outwards, so the whole droplet will be water soluble. And the stain is gone!

Seems like Jenny also has a stain she has to get rid of. Oh, greasy oil from bicycle chains is difficult to remove. Not even soap is enough to remove all of it. But Michael has an idea. First we need something that is even more nonpolar than soap.

Like hand cream. Or cooking oil. Then we apply it to the tough greasy stains. And let it sit for a few minutes. Look, the cooking oil managed to dissolve the stains.

Now all she has to do is wash away the cooking oil with soap. So if you want to get rid of a particularly greasy stain, use the rule "like dissolves like", and dissolve it in oil first!