Last we, we explored just a little bit about the science behind salads. We specifically looked at how to bring leaf lettuce back from the dead (almost). Don’t think for one minute that we are done looking at vegetables and salads. We’re NOT!
This week, we have to add something to our salad. Something that ALL of us use in one form or another (unless you are a rabbit!) That’s right. This week we are going to look at…
Salad Dressing!
The four main concepts of science we explore each week can easily be observed with our favorite saucy topping so let’s review them a bit:
Excellent. Now we can get down to business…
The easiest and most common salad dressing is known as a VINAIGRETTE which is a fancy word for “a mixture of oil and vinegar.” All you need to do to make vinaigrette is add three parts oil to one part vinegar (i.e. 300mL of Olive Oil and 100mL of Vinegar), the herbs and spices you prefer, and gently shake the mixture before pouring it on your salad. But how do you get such a great flavor from a mixture of these items?
THE SECRET IS IN THE ATOMS
Scientists call a vinaigrette an EMULSION which means that the ATOMS within the oil and vinegar do not rearrange themselves when they are mixed together. They hold on to each other!
Any salad dressing that is an EMULSION can easily be found in any salad dressing aisle of your local grocery store. They are really easy to find! All you have to look for are the containers with two layers of liquids just resting in place.
HOW DARE YOU CALL MY SALAD DRESSING “DENSE!”
Many people would incorrectly say that the top layer (the oil) rests on top of the bottom layer (the vinegar and spices) because the oil is lighter than the vinegar.
This is not true!
As I explained in my Classic Science: Chemistry curriculum, the layers you find in this tasty salad dressing take place because of a difference in DENSITY! Remember, DENSITY is the amount of ATOMS found within a certain amount of an object. So, if you were to measure out one cup of oil and one cup of vinegar, you would find that the total number of atoms within the cup of oil would be smaller than in the vinegar. To put it simply…
Oil is less DENSE than vinegar so the oil floats on top.
VINAIGRETTE IS VERY SNEAKY
If you have ever placed any kind of oil in your hands like lotion, cooking oil, motor oil, you probably figured out how quickly this stuff spreads all over your hands. Even if you scrub really hard, you STILL can feel some of that oily mixture on you! This stuff gets everywhere!
Another way to say this is…
The molecules of oil DIFFUSE very easily onto dry surfaces.
Although this may be nuisance if oil gets on your hands, it is a VERY good property of vinaigrettes.
Since the oil in vinaigrette DIFFUSES very well, it clings to vegetables like lettuce very easily. And when the vinegar and spices are mixed in with the oil after a good shaking, the flavorful vinegar DIFFUSES around your salad too!
Just remember to keep your salad dry before adding the vinaigrette. The oil will not be able to DIFFUSE onto the salad if the vegetables are covered in water!
THE MYSTERIOUS LAW INSIDE YOUR SALAD DRESSING
Shaking up an EMULSION doesn’t change any of the ATOMS at all. You already know that ATOMS cannot be created or destroyed, only rearranged.
However, it does not mean that the atoms HAVE to rearrange!
So go ahead and shake that bottle of Italian dressing as hard as you like. It may look like you’ve created a whole new chemical, but you are only mixing up an EMULSION.
Learn more about emulsions and other chemistry concepts in Classic Science: Chemistry for the Family and be certain to come back every Thursday or subscribe to The Blog of Mr.Q to learn more about how to teach science with cheap, everyday items!
