Material That Can Absorb Water Vapour From Air but Use Again and Again

Phenomenon of attracting and holding water molecules

Hygroscopy is the phenomenon of alluring and belongings h2o molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules go suspended amidst the substance'south molecules, adsorbing substances can become physically changed, e.one thousand., irresolute in volume, boiling point, viscosity or some other physical characteristic or property of the substance.

Deliquescent materials are sufficiently hygroscopic that they absorb and then much water that they become liquid and grade an aqueous solution.

Apparatus for the conclusion of the hygroscopicity of fertilizer, Fixed Nitrogen Research Laboratory, ca. 1930

Etymology and pronunciation [edit]

The word hygroscopy () uses combining forms of hygro- and -scopy. Unlike whatever other -scopy word, it no longer refers to a viewing or imaging fashion. It did begin that way, with the word hygroscope referring in the 1790s to measuring devices for humidity level. These hygroscopes used materials, such as certain animal hairs, that appreciably changed shape and size when they became clammy. Such materials were and then said to be hygroscopic considering they were suitable for making a hygroscope. Eventually, though, the give-and-take hygroscope ceased to be used for whatsoever such instrument in modern usage. Just the discussion hygroscopic (tending to retain wet) lived on, and thus also hygroscopy (the power to exercise then). Nowadays an instrument for measuring humidity is called a hygrometer (hygro- + -meter).

Overview [edit]

Hygroscopic substances include cellulose fibers (such as cotton and paper), sugar, caramel, honey, glycerol, ethanol, wood, methanol, sulfuric acrid, many fertilizer chemicals, many salts (like calcium chloride, bases like sodium hydroxide etc.), and a wide variety of other substances.[i]

If a compound dissolves in h2o, and so it is considered to be hydrophilic.[two]

Zinc chloride and calcium chloride, equally well as potassium hydroxide and sodium hydroxide (and many dissimilar salts), are so hygroscopic that they readily dissolve in the water they absorb: this belongings is called deliquescence. Not just is sulfuric acid hygroscopic in concentrated class but its solutions are hygroscopic down to concentrations of 10% v/v or below. A hygroscopic material volition tend to become clammy and cakey when exposed to moist air (such as the common salt within salt shakers during humid weather).

Because of their affinity for atmospheric moisture, hygroscopic materials might require storage in sealed containers. When added to foods or other materials for the express purpose of maintaining moisture content, such substances are known equally humectants.

Materials and compounds exhibit different hygroscopic backdrop, and this difference can lead to detrimental effects, such as stress concentration in blended materials. The volume of a detail material or compound is affected past ambient wet and may be considered its coefficient of hygroscopic expansion (CHE) (also referred to as CME, or coefficient of moisture expansion) or coefficient of hygroscopic contraction (CHC)—the difference between the two terms beingness a divergence in sign convention.

Differences in hygroscopy can be observed in plastic-laminated paperback book covers—often, in a suddenly moist environs, the book cover volition curl away from the balance of the book. The unlaminated side of the comprehend absorbs more wet than the laminated side and increases in expanse, causing a stress that curls the cover toward the laminated side. This is similar to the office of a thermostat's bimetallic strip. Inexpensive dial-blazon hygrometers brand use of this principle using a coiled strip. Deliquescence is the process by which a substance absorbs wet from the atmosphere until it dissolves in the absorbed water and forms a solution. Deliquescence occurs when the vapour pressure level of the solution that is formed is less than the partial pressure of water vapour in the air.

While some like forces are at work here, it is different from capillary attraction, a procedure where glass or other solid substances attract water, but are not changed in the process (e.g., water molecules do not become suspended between the glass molecules).

Engineering properties [edit]

The corporeality of moisture held by hygroscopic materials is commonly proportional to the relative humidity. Tables containing this data tin be found in many engineering handbooks and is as well available from suppliers of various materials and chemicals.

Hygroscopy too plays an important part in the engineering of plastic materials. Some plastics, east. k. nylon, are hygroscopic while others are not.

Biology [edit]

The thorny dragon features hygroscopic grooves between the spines of its pare to capture water in its desert habitat.

The seeds of some grasses have hygroscopic extensions that curve with changes in humidity, enabling them to disperse over the ground. An example is Needle-and-Thread, Hesperostipa comata.[3] Each seed has an awn that twists several turns when the seed is released. Increased wet causes information technology to untwist, and, upon drying, to twist again, thereby drilling the seed into the ground.

Thorny dragons collect moisture in the dry desert via nighttime condensation of dew that forms on their skin and is channeled to their mouths in hygroscopic grooves betwixt the spines of their skin. H2o also collects in these grooves when it rains. Capillary action allows the lizard to suck in water from all over its trunk.

Deliquescence [edit]

Deliquescence, like hygroscopy, is also characterized by a strong affinity for water and tendency to absorb wet from the atmosphere if exposed to information technology. Unlike hygroscopy, however, deliquescence involves absorbing sufficient water to form an aqueous solution. Almost deliquescent materials are salts, including calcium chloride, magnesium chloride, zinc chloride, ferric chloride, carnallite, potassium carbonate, potassium phosphate, ferric ammonium citrate, ammonium nitrate, potassium hydroxide, and sodium hydroxide. Owing to their very high affinity for h2o, these substances are often used as desiccants, too an application for concentrated sulfuric and phosphoric acids. Some deliquescent compounds are used in the chemical manufacture to remove water produced by chemical reactions (see drying tube).[4]

Polymers [edit]

Many engineering polymers are hygroscopic, including nylon, ABS, polycarbonate, cellulose, carboxymethyl cellulose, and poly(methyl methacrylate) (PMMA, plexiglas, perspex).

Other polymers, such as polyethylene and polystyrene, do non commonly blot much moisture, but are able to behave meaning moisture on their surface when exposed to liquid water.[5]

Type-6 nylon (a polyamide) tin blot up to 9.v% of its weight in moisture.[6]

Applications in baking [edit]

The employ of different substances' hygroscopic properties in baking are oftentimes used to achieve differences in wet content and, hence, crispiness. Dissimilar varieties of sugars are used in different quantities to produce a crunchy, crisp cookie (UK: biscuit) versus a soft, chewy cake. Sugars such as honey, chocolate-brown sugar, and molasses are examples of sweeteners used to create more moist, chewy cakes.[seven]

See also [edit]

  • Efflorescent
  • Hydrophile
  • Hydrophobe
  • Critical relative humidity
  • Equilibrium moisture content

References [edit]

  1. ^ "Hygroscopic compounds". hygroscopiccycle.com. IBERGY. Archived from the original on April eight, 2017. Retrieved April 7, 2017.
  2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Aureate Volume") (1997). Online corrected version: (2006–) "hydrophilic". doi:x.1351/goldbook.H02906
  3. ^ Burn down Effects Data Arrangement, Species: Hesperostipa comata Archived 2017-05-28 at the Wayback Auto U.S. Section of Agriculture Wood Service.
  4. ^ Wells, Mickey; Wood, Daniel; Sanftleben, Ronald; Shaw, Kelley; Hottovy, Jeff; Weber, Thomas; Geoffroy, Jean-Marie; Alkire, Todd; Emptage; Sarabia, Rafael (June 1997). "Potassium carbonate as a desiccant in effervescent tablets". International Journal of Pharmaceutics. 152 (2): 227–235. doi:x.1016/S0378-5173(97)00093-eight.
  5. ^ Schwartz, S., Goodman, South. (1982). Plastics Materials and Processes, Van Nostrand Reinhold Company Inc. ISBN 0-442-22777-9, p.547
  6. ^ "NYLON". sdplastics.com. San Diego Plastics, Inc. Archived from the original on May 13, 2017. Retrieved April 7, 2017.
  7. ^ Sloane, T. O'Conor. Facts Worth Knowing Selected Mainly from the Scientific American for Household, Workshop, and Farm Embracing Practical and Useful Information for Every Branch of Industry. Hartford: S. S. Scranton and Co. 1895.

External links [edit]

  • Video on the deliquescense of calcium chloride
  • The movement of hygroscopic organic salts

smithnottakeling.blogspot.com

Source: https://en.wikipedia.org/wiki/Hygroscopy

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