If you’ve ever tried to make salad dressing indigenous scratch, you understand that one of the biggest challenges is obtaining the oil and the vinegar come mix properly. No issue how tough you try to shake, stir, or whisk oil and also vinegar together, they eventually separate. This happens because vinegar and also oil space made of very different varieties of molecules that room attracted come their very own kind.

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The electronegative oxygen in a water molecule pulls electrons away from the 2 hydrogens, creating an uneven circulation of charge within the molecule.

Most vinegars are options of acetic acid and water (plus some various other acids and also alcohols, depending upon the type of vinegar you room using). Water, acetic acid, and also alcohol space all examples of polar molecules—molecules that have actually a slightly an adverse charge at one end, or pole, and also a slightly positive charge at another end. These slightly charged poles arise due to the fact that one or much more atoms in the molecule are electronegative, definition that lock tug electrons—which are negatively charged—towards them, producing an uneven distribution of charge within the molecule. Polar molecules are normally attracted to other polar molecules due to the fact that their slightly an adverse poles have an affinity for your slightly confident poles. Polar molecules room attracted come water molecules—which are likewise polar—and are called hydrophilic, i beg your pardon means “water loving.”

Oils are a different story. Oils room a kind of fat (like butter, shortening, and also lard) and are thought about non-polar. Fats and also oils space composed mostly of lengthy molecules called fatty acids (usually bound with each other by glycerol molecules into teams of 3 called triglycerides). Most of the atom in a fatty mountain molecule share electrons evenly and also are neither negatively nor positively charged (although fatty acids do contain tiny regions of polarity—just not sufficient to make the totality molecule polar.) Non-polar molecules love various other non-polar molecules and will glom together when combined with water. You have the right to observe this phenomenon by placing a couple of drops the oil on the surface ar of a key of water—eventually the drops will kind a single big oil slick. Oils repel polar molecule such together those discovered in vinegar. Since oils likewise repel water, they are dubbed hydrophobic, which method “water-fearing.”

The carbon (black) and also hydrogen (white) in this non-polar fatty mountain molecule share electron evenly and are no negatively or positively charged.

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How have the right to we bring together polar and non-polar molecules to do something delicious like mayonnaise (which is basically a combination of water and oil) or salad dressing? We need an emulsifier. Emulsifiers space the hand-holders the the molecule world. Lock contain both hydrophobic and hydrophilic regions and also are able come attract and “hold hands” through polar and non-polar molecule simultaneously, pulling them together to type a special type of mixture called an emulsion. For instance, after including an reliable emulsifier to oil and vinegar and also mixing thoroughly, separation that the oil indigenous the vinegar will certainly take much longer or won’t take place at all.


In this experiment, you will test a few common family members ingredients to watch which is the most efficient emulsifier for making salad dressing—and you can eat your results!