If you’ve ever tried to make salad dressing from scratch, you know that one of the biggest obstacles is acquiring the oil and the vinegar come mix properly. No issue how hard you try to shake, stir, or whisk oil and also vinegar together, they eventually separate. This happens since vinegar and oil space made of an extremely different varieties of molecule that room attracted to their own kind.

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

Most vinegars are solutions of acetic acid and water (plus some various other acids and alcohols, depending on the form of vinegar you space using). Water, acetic acid, and also alcohol are all instances of polar molecules—molecules that have a slightly an adverse charge in ~ one end, or pole, and a slightly confident charge at an additional end. This slightly charged poles arise due to the fact that one or more atoms in the molecule space electronegative, definition that castle tug electrons—which space negatively charged—towards them, creating an uneven distribution of charge within the molecule. Polar molecules are usually attracted to various other polar molecules because their slightly negative poles have actually an affinity for your slightly positive poles. Polar molecules space attracted to water molecules—which are also polar—and are referred to as hydrophilic, i beg your pardon means “water loving.”

Oils are a various story. Oils room a kind of fat (like butter, shortening, and lard) and also are thought about non-polar. Fats and also oils room composed mostly of long molecules called fatty mountain (usually bound together by glycerol molecules into groups of three called triglycerides). Most of the atom in a fatty acid molecule share electron evenly and also are no negatively no one positively charged (although fatty acids carry out contain tiny regions of polarity—just not enough to do the entirety molecule polar.) Non-polar molecule love various other non-polar molecules and also will glom with each other when combined with water. You deserve to observe this phenomenon by placing a few drops of oil ~ above the surface ar of a key of water—eventually the autumn will kind a single large oil slick. Oils repel polar molecule such together those uncovered in vinegar. Since oils additionally repel water, castle are dubbed hydrophobic, which method “water-fearing.”

The carbon (black) and hydrogen (white) in this non-polar fatty acid molecule share electrons evenly and are neither negatively or positively charged.

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How deserve to we lug together polar and also non-polar molecule to make something delicious prefer mayonnaise (which is basically a combination of water and oil) or salad dressing? We need an emulsifier. Emulsifiers room the hand-holders of the molecule world. They contain both hydrophobic and hydrophilic regions and also are able to attract and also “hold hands” v polar and non-polar molecules simultaneously, pulling them with each other to form a special type of mixture called an emulsion. Because that instance, after including an efficient emulsifier to oil and vinegar and mixing thoroughly, separation of the oil indigenous the vinegar will certainly take much longer or won’t occur at all.


In this experiment, you will certainly test a few common family members ingredients to view which is the most efficient emulsifier because that making salad dressing—and you deserve to eat her results!