Forget salting – should we be gummy-bearing roads in the winter to prevent icing? When it comes to antifreeziness it’s the numbers of dissolved things that matter, so why not use something sweet to coat our street? In the ANTIFREEZE dance you dance in super slow-mo but “never” freeze because of the colligative property of FREEZING-POINT DEPRESSION. Instead of crying over degraded proteins, take the CRYOPROTECTANT candy challenge 🍬 NERDS™️ often win because of how many pieces you can stuff in! 🤓

At any given temperature/pressure combo a substance prefers to be SOLID, LIQUID, or GAS & @ specific temps, they’ll undergo a PHASE CHANGE where they switch states (e.g. they go LIQUID ➡️ SOLID @ FREEZING POINT ❄️ )

👆 temps depend on what substance’s made of (e.g. PURE water freezes at 0°C (32°F (WHY, 🇺🇸 WHY?! 😩)). BUT adding SOLUTE (dissolving things in it) changes them👇

Water’s “sticky” (it has strong INTERMOLECULAR FORCES (IMFs) & SOLUTE breaks up some of the “stickiness” so water molecules are “freer” 👉 ⬆️ ENTROPY (randomness) 🎲 of the liquid 👉 Nature likes entropy 👍 so liquid becomes a “happier place” 😃

The MORE dissolved particles you have in a liquid solution, the happier it is as a liquid 😃😃 & the more it wants to REMAIN A LIQUID 🤚

So it’s harder to get it to VAPORIZE (go LIQUID ➡️ GAS) 👉 we call this VAPOR PRESSURE DEPRESSION ⬇️ & it leads to BOILING POINT ELEVATION ⬆️ ♨️♨️

AND it’s also harder to go the “other way” 👉 have to remove more heat (get to ⬇️ temp) in order to FREEZE (go LIQUID ➡️ SOLID) ❄️❄️👉 we call this FREEZING POINT DEPRESSION ⬇️

So, if you want to PREVENT something from FREEZING, don’t get it cold… or ADD SOLUTE! 🤗 We call solutes we add to prevent freezing CRYOPROTECTANTS 👍

Water’s weird in that it EXPANDS when it freezes 🤯 MOST LIQUIDS DON’T! Water does bc it freezes in an orderly lattice (which solute “gets it the way” of 👍) in which, in order to achieve optimal binding angles, it has to spread out

⏩ if water freezes inside pipes, they can burst 😬 & if it freezes inside our protein crystals (where “rivers” of solvent flow through gaps in the protein’s 3D structure), they can “break” 😬😬 So we add CRYOPROTECTANTS to protect pipes in winter & crystals when we freeze them (we want PROTEIN crystals NOT water crystals!)⚠️. 

What to add? 🤔👇

FREEZING POINT DEPRESSION is a COLLIGATIVE PROPERTY (as are vapor pressure depression & boiling point elevation), meaning it’s the # of dissolved particles, not the identity of the particles that matters 👍

So you might think, why not add an ELECTROLYTE like NaCl (table salt) which dissociates into its component ions (charged particles) when you dissolve it (e.g. (Na⁺ & Cl⁻), giving you more particles than you put in? 🤷‍♀️ 

You could, & this is why we salt our streets to prevent them from icing over💡BUT the “2-for-1-ness”of salt is really just a result of chemists’ book-keeping 👉 how we define the “formula unit” (akin to what you “buy it as”) which we use in our calculations

For our candy analogy, we compared a Kit-Kat bar to a NON-ELECTROLYTE like table sugar (sucrose) & a Rolo roll to an ELECTROLYTE like NaCl. 👉 We call each of these “1 candy bar” even though the roll of Rolos has 7 individual pieces of candy inside. If we had instead called the Rolos bar 7 pieces it wouldn’t be like we were getting more 👍

Similarly, we call 1 “NaCl” 1 formula unit even though in solution it’s really 1 Na⁺ & 1 Cl⁻. If we had accounted for this before adding it, we could say we add 1 Na+ and 1 Cl- & it wouldn’t seem like we’re getting more than we expected 👍

So don’t be fooled by the “false advertising.” If you don’t like Rolos, don’t buy a Rolos roll just bc you want more pieces of candy! You can buy 7 individually-wrapped candies instead & as long as they’re small enough, you can still stuff them in your pocket 🤗
So, free yourself by thinking about buying individual pieces of candy instead of bars & get picky! Do you want something chewy? Hard? Sour? Sweet? It probably depends on the situation, & same’s true for chemical & biochemical reactions 👍

The # of particles is all we care about in terms of freezing prevention, but it’s NOT all we care about for other things! ⚠️

Salt comes with a high charge – literally!⚡️ Because it breaks into charged particles, it can have undesirable consequences (like breaking up IMFs in our protein not just the water!😬) or corroding metals 😬

We want to add something that’s more “water-like” in terms of not disrupting the system (but less water-like in terms of “stickiness”) 👉 Basically, we want something kinda “blah” – and SMALL so we can pack lots of it in there 👉 small polyols (chemicals with multiple -OH groups) like GLYCEROL & ETHYLENE GLYCOL fit the bill & are commonly used as CRYOPROTECTANTS 👍

more on topics mentioned (& others) #365DaysOfScience All (with topics listed) 👉 

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