A cooling bath or ice bath, in laboratory chemistry practice, is a liquid mixture which is used to maintain low temperatures, typically between 13 °C and −196 °C. These low temperatures are used to collect liquids after distillation, to remove solvents using a rotary evaporator, or to perform a chemical reaction below room temperature (see Kinetic control).

Cooling baths are generally one of two types: (a) a cold fluid (particularly liquid nitrogen, water, or even air) — but most commonly the term refers to (b) a mixture of 3 components: (1) a cooling agent (such as dry ice or ice); (2) a liquid "carrier" (such as liquid water, ethylene glycol, acetone, etc.), which transfers heat between the bath and the vessel; (3) an additive to depress the melting point of the solid/liquid system.

A familiar example of this is the use of an ice/rock-salt mixture to freeze ice cream. Adding salt lowers the freezing temperature of water, lowering the minimum temperature attainable with only ice.

+ Mixed solvent cooling baths (% by volume) % Glycol in EtOH Temp (°C) % H2O in MeOH Temp (°C) 0% −78 0% −97.6 10% −76 14% −128 20% −72 20% N/A 30% −66 30% −72 40% −60 40% −64 50% −52 50% −47 60% −41 60% −36 70% −32 70% −20 80% −28 80% −12.5 90% −21 90% −5.5 100% −17 100% 0

Mixed-solvent cooling baths Mixing solvents creates cooling baths with variable freezing points. Temperatures between approximately −78 °C and −17 °C can be maintained by placing coolant into a mixture of ethylene glycol and ethanol, while mixtures of methanol and water span the −128 °C to 0 °C temperature range.Methanol/Water mixtures make great cooling baths. Chemtips.wordpress.com. Retrieved on 2015-02-23.The ridiculously thorough guide to making a MeOH/Water bath. Chemtips.wordpress.com. Retrieved on 2015-02-23. Dry ice sublimes at −78 °C, while liquid nitrogen is used for colder baths.

As water or ethylene glycol freeze out of the mixture, the concentration of ethanol/methanol increases. This leads to a new, lower freezing point. With dry ice, these baths will never freeze solid, as pure methanol and ethanol both freeze below −78 °C (−98 °C and −114 °C respectively).

Relative to traditional cooling baths, solvent mixtures are adaptable for a wide temperature range. In addition, the solvents necessary are cheaper and less toxic than those used in traditional baths.

Traditional cooling baths + Traditional cooling bath mixturesCooling baths – ChemWiki. Chemwiki.ucdavis.edu. Retrieved on 2013-06-17. Cooling agent Organic solvent or salt Temp (°C) Dry icep-xylene +13Dry iceDioxane +12Dry iceCyclohexane +6Dry iceBenzene +5Dry iceFormamide +2IceSalts (see: left) 0 to −40Liquid N2Cycloheptane −12Dry iceBenzyl alcohol −15Dry iceTetrachloroethylene −22Dry iceCarbon tetrachloride −23Dry ice1,3-Dichlorobenzene −25Dry iceo-Xylene −29Dry icem-Toluidine −32Dry iceAcetonitrile −41Dry icePyridine −42Dry icem-Xylene −47Dry icen-Octane −56Dry iceIsopropyl ether −60Dry iceAcetone −78Liquid N2Ethyl acetate −84Liquid N2n-Butanol −89Liquid N2Hexane −94Liquid N2Acetone −94Liquid N2Toluene −95Liquid N2Methanol −98Liquid N2Cyclohexene −104Liquid N2Ethanol −116Liquid N2n-Pentane −131Liquid N2Isopentane −160Liquid N2(none) −196

Water and ice baths A bath of ice and water will maintain a temperature 0 °C, since the melting point of water is 0 °C. However, adding a salt such as sodium chloride will lower the temperature through the property of freezing-point depression. Although the exact temperature can be hard to control, the weight ratio of salt to ice influences the temperature: −10 °C can be achieved with a 1:2.5 mass ratio of calcium chloride hemihydrate to ice. −20 °C can be achieved with a 1:3 mass ratio of sodium chloride to ice.

Dry ice baths at −78 °C Since dry ice will sublime at −78 °C, a mixture such as acetone/dry ice will maintain −78 °C. Also, the solution will not freeze because acetone requires a temperature of about −93 °C to begin freezing.

Safety recommendations The American Chemical Society notes that the ideal organic solvents to use in a cooling bath have the following characteristics: Nontoxic vapors. Low viscosity. Nonflammability. Low volatility. Suitable freezing point. In some cases, a simple substitution can give nearly identical results while lowering risks. For example, using dry ice in 2-propanol rather than acetone yields a nearly identical temperature but avoids the volatility of acetone (see below).

See also List of cooling baths Pumpable ice technology

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