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All systems that generate heat — from automobile engines to living organisms — need coolant fluids to absorb the heat and transfer it somewhere else. Water is a pretty effective coolant, but if i t freezes, it can expand enough to burst the rigid enclosure of an engine or electronic. To avoid icy explosions every time the temperature dips below freezing, we use antifreeze to change the water into a different chemical solution with a lower freezing point. Antifreeze works because the freezing and boiling points of liquids are “colligative” properties. This means they depend on the concentrations of “solutes,” or dissolved substances, in the solution. A pure solution freezes because the lower temperatures cause the molecules to slow down. This allows the natural attractive forces between molecules to capture and bind them into rigid crystalline structures. But adding a different kind of molecule to the mix blocks those attractive forces and prevents the crystal structures from forming. The more solutes are added, the lower the temperature needs to drop before the solution can properly freeze. SEE ALSO: 5 Things You Didn't Know About DNAThat’s why we sprinkle salt on roads and sidewalks to keep ice from forming in the winter. The salt and water mix into a solution that has a lower freezing point than water alone, so we don’t have to worry about ice until it gets much colder. But we can’t use salt as an antifreeze in mechanical cooling systems because of a few limiting factors. In addition to dissolving in water — which salt does quite admirably — a useful antifreeze needs to remain chemically inert, meaning that it doesn’t interact with the surfaces of the system. That rules out salt, which corrodes metal. Antifreeze also has to be easy and safe to produce, and come with a high boiling point that will prevent the system from building up pressure. Ethylene glycol fulfills all those criteria. A 50% ethylene glycol solution freezes at -37 degrees Celsius (-34.6 °F) instead of 0 degrees Celsius (32 °F), which makes it pretty ideal for most engines. Antifreeze in NatureSince living cells are full of water, they’re also in danger of forming lethal ice crystals that can rupture the cell in subzero environments. But a few organisms have built-in mechanisms to avoid freezing to death. Some of them simply dissolve extra sugars and glycerol molecules in the fluids bathing their cellular structures, creating a sort of intracellular (meaning “inside the cell”) antifreeze. But some organisms also make special “antifreeze proteins.” These proteins bind to the surfaces of very small ice crystals and prevent them from recrystallizing into larger, more lethal structures. Antifreeze proteins have been observed in bacteria, fungi, fish, plants, and insects. Naturally, these antifreeze proteins can be used in a variety of medical and commercial applications. Researchers are testing their potential to enhance the preservation of transplant organs, prevent frostbite, and make fish and crops more resistant to cold temperatures. But the most important breakthrough in the application of antifreeze proteins may be the development of smoother ice creams that don’t form those annoyingly gritty ice crystals. After all, the importance of surviving hypothermia pales in comparison to enjoying a perfectly textured, frozen delight. The roles of logistics in the economics and organisation.pptx Acute Abdomen and Appendicitis.docx Source Circular Functions Mathplanet accessed December 9 2020 document 381726401-SOTO-WEEK-4-SEDATIVE-HYPNOTICS-docx.docx University_of_Venda_v_M___others__2017__38_ILJ_1376__LC_.pdf MHA 705 Assignment 6.docx Barkley_ Cardio questions.docx
⚙️ Learning Objectives
The freezing point of a solution is lower than the freezing point of a pure solvent, which is why the phenomenon is called freezing point depression. The freezing point of a substance is the temperature at which the liquid changes into a solid. At a given temperature, if a substance is added to a solvent (such as water), the solute-solvent interactions prevent the solvent from transitioning into the solid phase. The solute-solvent interactions require the temperature to decrease further (slowing the particles down) in order to solidify the solution. Salt is placed onto roads and sidewalks in the winter to prevent water from freezing at the normal temperature of 0°C and, instead, causing it to freeze at a lower temperature, sometimes as low as –10°C to –15°C. De-icing planes is another common example of freezing point depression in action. A number of solutions are used, but commonly a solution such as ethylene glycol, or a less toxic monopropylene glycol, is used to de-ice aircraft. Aircrafts are sprayed with the solution when the temperature is predicted to drop below the freezing point. Yet another example of freezing point depression is the addition of antifreeze to a car radiator. This prevents the radiator from freezing in the winter. Freezing water can cause an engine block to crack, since water expands upon freezing. Freezing point depression is observed for any solute added to a solvent; the freezing point of the solution will always be lower than the freezing point of the pure solvent (without the solute). Thus, when anything is dissolved in water, the solution will freeze at a lower temperature than pure water.
Pure water boils at 100°C at 1 atm of pressure. When table salt is added to water, the resulting solution has a higher boiling point than pure water. Since the addition of a solute increases the boiling point, the colligative property is called boiling point elevation. In the case of salt, the boiling point increases because the ions form an attraction with the water molecules that prevents them from escaping as easily into the gaseous phase. In order for a saltwater solution to boil, the temperature must be raised above 100°C at 1 atm of pressure. Boiling point elevation is observed for any nonvolatile solute (one that does not evaporate easily) that is added to a solvent; the boiling point of a solution will always be higher than the boiling point of the pure liquid. One such application of boiling point elevation is the addition of antifreeze to a car radiator. Interestingly enough, the term antifreeze is rarely heard during the summer or in warmer climates. The term coolant is often used instead. When it comes to vehicles, antifreeze and coolant are the same thing – they are the same chemical(s); it just depends on the season or whether a person lives in a colder climate or warmer climate. While antifreeze/coolant will prevent water from freezing when the ambient temperature is very cold, it will also prevent the water in the radiator from boiling over when the ambient temperature is very warm. Should the water in a radiator and engine block boil away, it will cause the engine to overheat causing certain parts attached directly to the engine to warp or gaskets to blow out.
Before we introduce the final colligative property, we need to present a new concept. A semipermeable membrane is a thin membrane that allows certain small molecules to pass through, but not others. A thin sheet of cellophane, for example, acts as a semipermeable membrane (see Figure \(\PageIndex{3}\)(a)). The semipermeable membrane is used to separate two solutions having the different concentrations marked. Curiously, this situation is not stable; there is a tendency for water molecules to move from the dilute side (on the left) to the concentrated side (on the right) until the concentrations are equalized, as in Figure \(\PageIndex{3}\)(b). This tendency is called osmosis. In osmosis, the solute is unable to pass through the membrane and remains on its original side of the system; only solvent molecules move through the semipermeable membrane. In the end, the two sides of the system will have different volumes. Because a column of liquid exerts a pressure, there is a pressure difference (Π) between the two sides of the system that is proportional to difference in height between the two columns. This pressure difference is called the osmotic pressure. Osmotic pressure plays an important role in biological systems because cell walls are semipermeable membranes. In particular, when a person is receiving intravenous (IV) fluids, the osmotic pressure of the fluid needs to be approximately the same as blood serum to avoid any negative consequences. Figure \(\PageIndex{4}\) shows three red blood cells:
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