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Cooling bath
 
 
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A cooling bath is a mixture used in a laboratory
Laboratory

A laboratory is a facility that provides controlled conditions in which science research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories....
 when low temperatures are needed, for example to conduct low-temperature chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
s (such as when kinetic control of the reaction is desired), to collect highly volatile liquids from distillation
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
, or in cold trap
Cold trap

In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid. The most common objective is to prevent vapors from contaminating a vacuum pump....
s. It usually consists of a solid that melts or sublimes at a low temperature, or a liquid that boils at a low temperature, mixed with some other substance that modulate the temperature of the bath or improve heat conduction.

Types
The simplest and cheapest cooling bath is an ice/water mixture, which maintains a temperature of 0 °C.






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Aldolrxnpic
A cooling bath is a mixture used in a laboratory
Laboratory

A laboratory is a facility that provides controlled conditions in which science research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories....
 when low temperatures are needed, for example to conduct low-temperature chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
s (such as when kinetic control of the reaction is desired), to collect highly volatile liquids from distillation
Distillation

Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
, or in cold trap
Cold trap

In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid. The most common objective is to prevent vapors from contaminating a vacuum pump....
s. It usually consists of a solid that melts or sublimes at a low temperature, or a liquid that boils at a low temperature, mixed with some other substance that modulate the temperature of the bath or improve heat conduction.

Types


The simplest and cheapest cooling bath is an ice/water mixture, which maintains a temperature of 0 °C. For lower temperatures, three main types of cooling baths are typical:

Ice
A slurry of ice
Ice

Ice is a solid phases of matter, usually crystalline solid, of a non-metallic substance that is liquid or gas at room temperature, such as ammonia ice or methane ice....
 and an inorganic salt such as sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
 or calcium chloride
Calcium chloride

Calcium chloride, CaCl2, is a common Salt . It behaves as a typical ionic halide, and is solid at room temperature. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in concrete....
 can provide temperatures down to about -40 °C. The temperature depends on the amount and type of salt used, based on the freezing point depression effect.

Dry ice
A slurry of dry ice
Dry ice

Dry ice is solid carbon dioxide. It is commonly used as a versatile cooling agent.Dry ice Sublimation , changing directly to a gas at atmospheric pressure....
 and an organic solvent can provide temperatures down to about -78 °C.

Liquid nitrogen
Liquid nitrogen
Liquid nitrogen

Liquid nitrogen is a liquefied atmospheric gas produced industrially in large quantities by fractional distillation of liquid air. It is pure nitrogen in a liquid state at very low temperature....
, either used as-is, or with an organic solvent can provide temperatures down to about the boiling point of pure N2, -196 °C. The temperature depends on the freezing point of the organic solvent.

Advantages and disadvantages

Several factors influence the choice of the cooling bath composition. The first is availability — dry ice and liquid nitrogen are comparatively inexpensive, but dry ice is often more easily stored.

The toxicity and flammability of the composition also matters. For example, many of the solvents used with dry ice are flammable. This problem is mitigated because at the working temperatures, the vapor pressures of most of these solvents is non-hazardous. In most cases, a relatively non-toxic solvent such as acetone or diethyl ether
Diethyl ether

Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor....
 is preferred, than something more toxic like bromomethane
Bromomethane

The chemical compound bromomethane, commonly known as methyl bromide, is an Organobromide compound with chemical formula CarbonHydrogen3Bromine....
. When the cooling bath is no longer needed, the waste solvents also need to be stored and disposed of.

Liquid nitrogen is usually considered the best cooling bath refrigerant because it is non-toxic, is cheap, and leaves no residue. However, it suffers from the drawback of being cold enough to condense liquid oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 from the air. The co-condensation of organic solvents and oxygen is a potentially explosive mixture that must be avoided.

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