Miscibility

 ( Chemical Properties ) 

Miscibility () is the property of two substances to mix in all mixing ratio (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). Such substances are said to be (etymologically equivalent to the common term ""). The term is most often applied to , but also applies to and . An example in liquids is the miscibility of water and ethanol as they mix in all proportions.

By contrast, substances are said to be if the mixture does not form a solution for certain proportions. For one example, oil is not soluble in water, so these two solvents are immiscible. As another example, butanone (methyl ethyl ketone) is immiscible in water: it is soluble in water up to about 275 grams per liter, but will separate into two phases beyond that.

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Organic compounds In , the weight percent of hydrocarbon chain often determines the compound's miscibility with water. For example, among the alcohols, ethanol has two carbon and is miscible with water, whereas N-Butanol with four carbons is not.

(2013). 9780199655304, OUP Oxford. . ISBN 9780199655304

1-Octanol, with eight carbons, is practically insoluble in water, and its immiscibility leads it to be used as a standard for partition equilibria.

J. Sangster (1997). 9780471973973, John Wiley & Sons. . ISBN 9780471973973

The straight-chain up to Butyric acid (with four carbon atoms) are miscible with water, valeric acid (with five carbons) is partly soluble, and hexanoic acid (with six) is practically insoluble,

(2010). 9781439049143, Cengage Learning. . ISBN 9781439049143

as are longer and other ; the very long carbon chains of lipids cause them almost always to be immiscible with water. Analogous situations occur for other such as and .

Thus a practical rule of thumb for determining the solubility of an organic molecule in water (and/or other similarly polar solvents) is to consider the ratio of carbons in the molecule bound to polar functional groups (such as hydroxyl groups), to the number of simple hydrocarbons. If the molecule has a ratio of roughly 1:4 (Polar-to-non-polar carbons), it is soluble in water. It is however necessary to recognise this as a rule of thumb, and not always indicative.

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Metals Immiscible are unable to form with each other. Typically, a mixture will be possible in the molten state, but upon freezing, the metals separate into layers. This property allows solid precipitates to be formed by rapidly freezing a molten mixture of immiscible metals. One example of immiscibility in metals is copper and cobalt, where rapid freezing to form solid precipitates has been used to create granular GMR materials.

John C. Mallinson (2001). 9780080510637, Academic Press. . ISBN 9780080510637

Some metals are immiscible in the liquid state. One with industrial importance is that liquid zinc and liquid silver are immiscible in liquid lead, while silver is miscible in zinc. This leads to the Parkes process, an example of liquid-liquid extraction, whereby lead containing any amount of silver is melted with zinc. The silver migrates to the zinc, which is skimmed off the top of the two-phase liquid, and the zinc is then boiled away, leaving nearly pure silver.

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Effect of entropy If a mixture of has lower configurational entropy than the components, they are likely to be immiscible in one another even in the liquid state.

G. A. Webb (2025). 9780854043620, Royal Society of Chemistry. . ISBN 9780854043620

(2013). 9783527638499, John Wiley & Sons. . ISBN 9783527638499

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Determination Miscibility of two materials is often determined optically. When the two miscible liquids are combined, the resulting liquid is clear. If the mixture is cloudy the two materials are immiscible. Care must be taken with this determination. If the Refractive index of the two materials are similar, an immiscible mixture may be clear and give an incorrect determination that the two liquids are miscible.

(1997). 9780824797973, CRC Press. . ISBN 9780824797973

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See also

• Emulsion
• Heteroazeotrope
• ITIES
• Miscibility gap
• Multiphasic liquid

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