How do liquids stay homogeneous and not have settling issues, such as Coke or milk?
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It’s the difference between dissolving and making a suspension, when something dissolves into a liquid it becomes part of the liquid, think sugar in water, no matter how long you leave it that sugar stays evenly divided over the liquid. A suspension is tiny particles hovering in a liquid. If you give it enough time it will settle. Like the kind of apple juice that still has apple in it.
If your milk doesn’t have settling issues that is because it’s been left to settle and (some of) the cream skimmed off, then the rest of it shaken up real good (homogenised). Fresh milk separates.
But some (most) liquids don’t do this because there’s nothing to separate. Like water – what’s going to separate out of that?
For a product that has both water and oil, such as milk, it undergoes a process called homogenization. The product is forced through a super tiny opening at extremely high pressures. This breaks the large droplets of fat into tiny little specks.
However, products that have only been homogenized will still separate out over time. This is where ingredients called emulsifiers come into play. An emulsifier is a molecule that loves fat on one side and loves water on the other. After the milk is homogenized, the fat loving side of the emulsifier surrounds the tiny specks of fat. Now the outside of the speck loves water rather than fat. So whenever two specks of fat coated in emulsifier bump into each other, nothing happens because the fat in the specks cannot come back together to create a larger speck.
equilibrium is the function you are looking to learn about.
water is a highly dynamic substance. freaky really
Other people have weighed in on how homogenized milk is created, breaking up the fat globules into incredibly small molecules through incredibly fine filters.
It will settle and separate, but the degree of homogenization almost always guarantees that your milk will spoil well before that happens so no one ever actually sees it. Most store bought milk contains no emulsifiers
I left a glass of milk out. Poured it to drink before going on a 3 week vacation. When I returned home, I discovered I forgot to drink it, and it had separated into a thick white lower layer and clear liquid top layer. So maybe unknowingly shaking it every time you open a refrigerator door keeps its molecules bouncing around?
When something is dissolved in a liquid, it ionizes. If you look at the chemical structure, you can normally tell if something is soluble in water, as the chemical will be polar. For example, table salt (sodium chloride) is very ionizable in water. The sodium and chloride separates into ions that are stabilized by the polarity of water molecules.
“Like dissolves like” is something to consider when looking at solubility. Nonpolar solvents often solubilize nonpolar solutes and polar solvents solubilize polar solutes.
Coke is a homogenous mixture that mostly consists of water and sugar. Sugar is a polar organic compound that dissolves easily in water.
Milk is a heterogeneous mixture that consists of lipids and water. Lipids are long chains of hydrocarbons that are nonpolar, thus not dissolving in water. If milk is left to stand undisturbed for a long period of time, you’ll notice the separation.
Back in my youth, milk was not homogenized. You had to shake it everytime you took it out of the fridge. I still shake my milk cartons. Old habits die hard.
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