If you’ve ever before tried to do salad dressing from scratch, you understand that among the biggest difficulties is gaining the oil and also the vinegar to mix properly. No issue how hard you try to shake, stir, or whisk oil and vinegar together, they ultimately separate. This happens due to the fact that vinegar and oil room made of really different types of molecule that are attracted to their own kind.

You are watching: Why does oil and vinegar separate

The electronegative oxygen in a water molecule traction electrons far from the two hydrogens, developing an uneven distribution of fee within the molecule.

Most vinegars are services of acetic acid and water (plus some other acids and alcohols, depending on the kind of vinegar you are 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 hopeful charge at an additional end. This slightly fee poles arise because one or much more atoms in the molecule space electronegative, definition that they tug electrons—which are negatively charged—towards them, producing an uneven circulation of fee within the molecule. Polar molecules are usually attracted to various other polar molecules due to the fact that their slightly an unfavorable poles have an affinity for your slightly positive poles. Polar molecules are attracted to water molecules—which are likewise polar—and are referred to as hydrophilic, which means “water loving.”

Oils are a different story. Oils room a type of fat (like butter, shortening, and also lard) and are thought about non-polar. Fats and oils space composed generally of lengthy molecules referred to as fatty acids (usually bound with each other by glycerol molecules into teams of 3 called triglycerides). Most of the atoms in a fatty acid molecule share electron evenly and also are no negatively nor positively charged (although fatty acids do contain small regions of polarity—just not sufficient to do the totality molecule polar.) Non-polar molecule love various other non-polar molecules and will glom with each other when mixed with water. You deserve to observe this phenomenon by placing a few drops the oil ~ above the surface ar of a key of water—eventually the autumn will type a single huge oil slick. Oil repel polar molecule such as those found in vinegar. Due to the fact that oils also repel water, they are dubbed hydrophobic, which means “water-fearing.”

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

See more: How Far Is Chattanooga Tn From Nashville Tn To Chattanooga, Tn

How deserve to we carry together polar and also non-polar molecules to make something delicious prefer mayonnaise (which is essentially a mix of water and oil) or salad dressing? We need an emulsifier. Emulsifiers room the hand-holders that the molecule world. They contain both hydrophobic and also hydrophilic regions and are able come attract and “hold hands” with polar and also non-polar molecule simultaneously, pulling them together to kind a special form of mixture referred to as an emulsion. For instance, after including an efficient emulsifier to oil and vinegar and also mixing thoroughly, separation the the oil native the vinegar will take much much longer or won’t take place at all.

In this experiment, you will test a couple of common family members ingredients to see which is the most efficient emulsifier because that making salad dressing—and you can eat your results!