Why does salt "melt" snails and slugs? (And exactly how do people manage to prepare escargot without finishing up v a big pot that goo?)
To answer this question, let us take into consideration the snail as checked out by the chemist:
The snail is an animal whose sliding-along-the-plants part (the foot) is comprised of cells. Animal cells are, roughly, bags that aqueous solution and also organelles wrapped in phospholipid bilayers (the cell membranes). Because that what we"re looking in ~ here, the crucial thing to know is that cell membranes room semipermeable membranes: part stuff travel easily throughout the membrane, fan to its small size, while other stuff is too huge to pass with the membrane.
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There"s a particular property of semipermeable membranes v aqueous solutions on one of two people side called osmotic pressure. Roughly, this is the press on the membrane because of the remedies on one of two people side.
Let"s detour for a minute to solutions, and then we"ll return to what"s walk on with the semipermeable membrane.
A solution is a mixture of 2 or much more substances that is homogeneous. The contents of this mixture will associate with each other by method of intermolecular forces.
For plenty of solutions, there will be a relatively huge amount of one of the building materials (the solvent) and also a smaller amount of the other substance or building materials (the solute(s)). So, because that example, in a solution of sodium chloride (NaCl, additionally known together table salt), the NaCl is the solute and also the water is the solvent.
You"ll recall that solid NaCl is a lattice of Na+ and also Cl- held together through ionic bonds, strong electrostatic attractions in between the positively and also negatively charged ions. You"ll additionally recall the the H2O molecules in fluid water associate with each various other by method of hydrogen bonding (strong dipole-dipole attractions between the partial-positive hydrogen ends and also the partial-negative oxygen ends of the bordering water molecules). As soon as you dissolve NaCl in water, the ionic bonds between Na+ and Cl- are changed with ion-dipole interactions between these ions and also water. Here"s the chemist"s cartoon:
Notice that water molecules are arranged around Cl- v their partial-positive H-ends pointing in, if the water molecules approximately Na+ have their partial-negative O-ends point in. And, due to the fact that water is the solvent, you have the right to assume there room plenty that water molecules in the solution connecting with other water molecules by method of hydrogen bonding. An additional thing precious noting: Na+ and also Cl- ions are substantially larger than water molecules. (One method to talk about the dimension of ions, and also the magnitude of their optimistic or an unfavorable charge, is to to compare the average number of water molecules in your solvation shells.)
What happens once you put aqueous services on either side of a semi-permeable membrane? Those options will have tendency to shift whatever stuff have the right to be shifted throughout the membrane until the concentration (roughly, how much solute is liquified in the solution family member to the lot of solvent) is the exact same on both sides of the membrane. We might tell a comprehensive story about this in terms of energies and also entropies and also that sort of thing, yet we"re no going to go into those details today. Here, we execute fine noting the the water molecules are small enough to pass through the membrane, and that the solute (here, Na+ and also Cl- ions) space too huge to pass through the membrane. So the water will flow across the membrane, tending to flow from the side that has less solute come the side that has more solute. The net flow of water throughout the membrane stops when the solutions on both sides of the membrane have actually the same concentration. (At this point, water molecules are still passing v the membrane -- they"re little enough the the membrane won"t restrict their passage. However, when equilibrium has actually been achieved, the water molecules flow in both direction at the very same rate.)
As you might guess, you"ll view the biggest osmotic pressure in response to excessive concentration differences. Because that example, if you put a saline systems on one next of the membrane and also pure water on the various other side:
what will an outcome is a sirloin of water from the "pure" side to the "salt solution" next of the membrane. (Here, ns haven"t drawn the Na+ and also Cl- ions separately, because as far as the water is concerned, both are just stuff liquified in the systems that can"t get throughout the membrane.) In effect, the rush that water is trying to dilute the salt equipment so much that it"s indistinguishable from pure water. This usually outcomes in a swelling of the membrane, and also might even lead to it popping if it cannot contain all the extra water molecule that have rushed in.
Now let"s return to the snail.
The snail is made up of a bunch of cell which have actually aqueous solutions wrapped in semipermeable membranes. The content of the snail cells is no pure water -- there"re likely even some Na+ and Cl- ions kicking around in there. For this reason what wake up if friend place, on the other side of the membrane, a an extremely concentrated systems of NaCl?
Here, the water has tendency to cross the membrane in the direction that will dilute the NaCl to the very same concentration as what"s inside the snail cells. If there"s enough salt top top the salty side, this way pretty lot all the water within the snail cells will have to cross the membrane.
This kind of water-loss is not constant with the continued organic functioning (or structural integrity) that the snail.
At this point, you might point out that the bucket-of-salt method of dispatching snails doesn"t actually put a salt solution on the exterior that the snail cell membranes. However, snails excrete mucus to assist them on slide by reducing friction; the mucus consists of water. Also, the snails I"m picking have tendency to be out once the plants they"re slide on are wet through dew. In between the mucus and the dew, there"s enough water clinging to the exterior of the snail to dissolve part salt and put the membrane in call with a really salty solution. That"s enough to obtain the water flowing the end of the snail, i beg your pardon dissolves much more of the salt and also keeps the concentration high enough to "melt" the snail.
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So, exactly how on planet can you chef these critters -- consisting of seasoning to taste with salt -- without finishing up through a huge puddle the slime?
Cooking requires raising the temperature the the snails and their cells enough to denature the proteins in the snails. This raised temperature also changes the cell membranes -- ~ the cooking, the membranes are no longer semipermeable, however rather enable diffusion of water and also solute in both directions. This (plus the denaturing that the proteins within the snail cells) helps store the snail insides in, fairly than drawing all the water out and deflating the snail the was stop the water.