Chemical of the Week -- Lime

Chemical of the Week

LIME: CALCIUM OXIDE -- CaO

Calcium oxide is a white crystalline solid with a melting point of 2572°C. It is manufactured by heating limestone, coral, sea shells, or chalk, which are mainly CaCO3, to drive off carbon dioxide.

500–600°C

CaCO3(s)


--


CaO(s) + CO2(g)

This reaction is reversible; calcium oxide will react with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing carbon dioxide from the mixture as it is released.

The production of calcium oxide from limestone is one of the oldest chemical transformations produced by man. Its use predates recorded history. Most ancient languages have a word for calcium oxide. In Latin it is calx, from which the name of the element calcium is taken. In Old English, its name is lïm, which is the origin of the modern commercial name for calcium oxide, namely lime. The abundance of limestone in the Earth's crust and the ease of its transformation to calcium oxide do not alone explain why the lime is one of the oldest products of chemistry. Lime has many properties that make it quite valuable. It is so useful, that it is today produced industrially on a vast scale; over 20 million metric tons were produced in the U.S. in 2000.

The oldest uses of lime exploit its ability to react with carbon dioxide to regenerate calcium carbonate. When lime is mixed with water and sand, the result is mortar, which is used in construction to secure bricks, blocks, and stones together. Mortar is initially a stiff paste that is laid between the bricks. It gradually hardens, cementing the bricks together. At room temperature, the reaction of lime with carbon dioxide is very slow. It is speeded by mixing lime with water. When lime is mixed with water, it forms calcium hydroxide, called slaked lime.

CaO(s) + H2O(l)


--


Ca(OH)2(s)

The reaction of calcium hydroxide with carbon dioxide is faster, producing a mortar that hardens more quickly.

Ca(OH)2(s) + CO2(g)


--


CaCO3(s) + H2O(l)

Even with the increased reaction speed, mortar requires many years for complete reaction to occur. Other lime&endash;based products used in the construction industry include lime plaster and portland cement.

Perhaps the most commercially important property of lime is its ability to form solutions with silicates. When lime is heated with silica sand (SiO2) and sodium carbonate (Na2CO3), a solution is formed that does not crystallize when it is cooled. Instead it hardens to an amorphous, clear, and nearly colorless solid, namely glass. Because it is a mixture and not a pure compound, glass does not have a distinct melting point; it gradually softens as it is heated. Therefore, it can be molded and blown into many useful shapes. The production of glass from lime is another of the ancient uses of lime.

The most important modern use of lime also relies on its ability to form solutions with silicates. Nearly 45% of lime is used in the steel industry. Steel and iron are produced from ores, which are rocks that contain iron oxides. Many of these ores also contain a large amount of silicates. When lime is mixed with the ore and the mixture melted, these silicates combine with the lime, forming a liquid solution called slag. Slag is immiscible with molten iron, so the silicates can be removed from the iron by draining o the slag. Approximately 80 kg of lime is used in the production of each metric ton (1000 kg) of iron. Lime is also used in the production of other metals. For example, it is used to remove silicates from alumina (Al2O3) before the alumina is reduced to aluminum metal.

Lime is also an important material in the manufacture of chemicals. Its major use here is in the production of calcium carbide, CaC2. Calcium carbide is manufactured by heating lime with coke.

2 CaO(s) + 5 C(s)


--


2 CaC2(s) + CO2(g)

Calcium carbide reacts with water, releasing acetylene, C2H2.

CaC2(s) + 2 H2O(l)


--


C2H2(g) + Ca(OH)2(aq)

Acetylene is an important fuel for welding and is also a starting material for a range of organic compounds, including vinyl chloride, neoprene, and acrylonitrile, all of which are raw materials for polymers.

Pollution control is a rapidly expanding consumer of lime. Lime is used in stack gas scrubbers to reduce sulfur dioxide emissions from power plants. Sulfur dioxide reacts with lime to form solid calcium sulfite.

SO2(g) + CaO(s)


--


CaSO3(s)

Lime is also added to sewage to remove phosphates.

3 CaO(s) + 3 H2O(l) + 2 PO43–(aq)


--


Ca3(PO4)2(s) + 6 OH–(aq)

The pretreatment of water supplies involves the use lime to decrease the acidity, to soften, and to clear drinking water.

A variety of other industrial processes also make extensive use of lime. It is used as an opacifier in plastics. The paper industry uses it in pulping wood; because lime is highly alkaline, it dissolves the lignin that binds the fibers together in wood. In the refining of sugar, lime causes coagulation of plant material, allowing it to be more easily separated from the sugar syrup.

Calcium oxide no longer produces the limelight in theaters. The theatrical use of lime has disappeared, leaving only its name, suggesting the romance of a bygone era. Because lime has a very high melting point, it can be heated to a very high temperature without melting. Substances with such high melting points can be heated to white heat, a temperature so high that the light they emit is white. Before the advent of electric lighting, white stage lighting was produced by heating lime in the flame of a torch, and this light was called limelight.

Lime

* Citrus fruits
o Lime (fruit), various green to yellow fruits
+ Australian lime
+ Blood lime
+ Kaffir lime
+ Key lime
+ Persian lime
+ Citrus limetta
+ Limequat
+ Musk lime
* Spanish lime or mamoncillo
* Wild lime (Zanthoxylum fagara)
* Tilia, lime trees or lindens
o Tilia_×_europaea, common lime

[edit] Color

* Lime (color), the color halfway between yellow and chartreuse green

[edit] Chemicals, minerals, and materials

* Agricultural lime, pulverized rock containing primarily calcium carbonate
* Calcium oxide, also known as burnt lime, quicklime or unslaked lime
* Calcium hydroxide, also known as slaked lime, slack lime, pickling lime or hydrated lime
* Hydraulic lime
* Lime (material), a group of calcium compounds and minerals in which they predominate
* Lime mortar
* Lime plaster
* Lime water, common name for saturated calcium hydroxide solution

[edit] Places

* Lime Lake (disambiguation)
* Lime Township, Blue Earth County, Minnesota
* Lime, Oregon
* Limé, a French commune in the Aisne departments

[edit] Business and entertainment

* Lime (magazine)
* Lime Pictures
* Lime (TV), a lifestyle based content distribution
* Lime (band), a 1980s disco band
* Lime (Arvingarna album), by Swedish "dansband" Arvingarna
* A character from the anime series Saber Marionette J
* LIME (Landline, Internet, Mobile and Entertainment), formerly Cable & Wireless (Caribbean)

[edit] Other

* Limes, a border defense system of Ancient Rome
* LIME, a mobile middleware
* LIME, the airport code for Orio al Serio Airport, in Bergamo, Italy
* LimeWire, free peer-to-peer file sharing (P2P) client for the Java platform

[edit] See also

* Limey (disambiguation page)
* Liming (disambiguation)
* Lyme disease
* The Lives of Harry Lime
* Lima (disambiguation)
* Lemon

Original lime Defination

For other uses, see Lime (disambiguation).
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Unripened Key limes
Lime, raw (edible parts) Nutritional value per 100 g (3.5 oz)
Energy 126 kJ (30 kcal)
Carbohydrates 11 g
- Sugars 1.7 g
- Dietary fiber 3 g
Fat 0.2 g
Protein 0.7 g
Water 88 g
Vitamin C 29 mg (48%)
Percentages are relative to US recommendations for adults.
Source: USDA Nutrient database

Lime is a term referring to a number of different fruits, both species and hybrids, citruses, which are typically round, green to yellow in color, 3–6 cm in diameter, and containing sour and acidic pulp; they are a good source of vitamin C. Limes are often used to accent the flavours of foods and beverages. Limes are grown all year round and are usually smaller and sweeter than lemons.
Contents
[hide]

* 1 Uses
o 1.1 Cooking
o 1.2 Other uses
* 2 Production trends
* 3 Plants known as "lime"
* 4 Gallery
* 5 References

[edit] Uses
[edit] Cooking
Zesting a lime

In cooking, lime is valued both for the acidity of its juice and the floral aroma of its zest. It is a very common ingredient in authentic Mexican, Southwestern United States, Vietnamese and Thai dishes. It is also used for its pickling properties in ceviche. The use of dried limes (called black lime or loomi) as a flavouring is typical of Persian cuisine and Iraqi cuisine, as well as in Gulf-style baharat (a spice mixture that is also called kabsa or kebsa). Lime is an essential ingredient of any cuisine from India, and many varieties of pickles are made, e.g. sweetened lime pickle, salted pickle, and lime chutney.[1][2]

Lime leaves are also a herb in South, East, and Southeast Asia.

Lime is frequently used to add flavour to cold and hot drinks, including water, tonic and other cocktails.
[edit] Other uses

To prevent scurvy during the 19th century, British sailors were issued a daily allowance of citrus such as lemon, and later switched to lime,[3] which was not as effective at preventing scurvy but was easier to obtain on Britain's Caribbean colonies. It was later discovered that the greater effectiveness of lemons derived from the 4-fold higher quantities of vitamin C lemon juice contains compared to the West Indian limes used by the British.

Lime extracts and essential oils are frequently used in perfumes, cleaning products, and aromatherapy.

In India, the lime is used in Tantra for removing evil spirits. It is also combined with Indian chilis to make a protective charm to repel the evil eye.[4] Furthermore, it was believed that hanging limes over sick people cured them of the illness by repelling evil spirits lurking inside the body.
[edit] Production trends

India, with about 16% of the world's overall lemon and lime output, tops the production list, followed by Mexico (~14.5%), Argentina (~10%), Brazil (~8%) and Spain (~7%).
Promotional photo for California limes, 1948
Top ten lemon and limes producers — 2007
Country Production (Tonnes) Footnote
India 2060000 F
Mexico 1880000 F
Argentina 1260000 F
Brazil 1060000 F
Spain 880000 F
People's Republic of China 745100 F
United States 722000
Turkey 706652
Iran 615000 F
Italy 546584
World 13032388 A
No symbol = official figure, P = official figure, F = FAO estimate, * = Unofficial/Semi-official/mirror data, C = Calculated figure A = Aggregate (may include official, semi-official or estimates);

Source: Food And Agricultural Organization of United Nations: Economic And Social Department: The Statistical Division
[edit] Plants known as "lime"

* Australian limes
o Australian desert lime (Citrus glauca)
o Australian finger lime (Citrus australasica)
o Australian round lime (Citrus australis)
* Blood lime
* Kaffir lime (Citrus hystrix) (kieffer lime; makrut, or magrood)
* Key lime (Citrus aurantifolia) (Mexican, West Indian, or bartender's lime)
* Mandarin Lime (Citrus limonia)
* Musk lime (Citrofortunella mitis)
* Palestine sweet lime (Citrus x limettioides)
* Persian lime (Citrus x latifolia) (Tahiti or Bearss lime)
* Rangpur lime, a mandarin orange - lemon hybrid
* Spanish lime (Melicoccus bijugatus) (mamoncillo, mamón, ginep, quenepa, or limoncillo) (not a citrus)
* Sweet lime (Citrus limetta) (sweet limetta, Mediterranean sweet lemon)
* Wild lime (Adelia ricinella)
* Limequat (lime × kumquat)
* Lime tree (Tilia sp.)

[edit] Gallery

*
Limes whole and halved.jpg
*
Lime444.jpg
*

Kaffir lime fruit
*

Lime wedges are typically used in drinks
*

Grocery store limes
*

Lime and Blossom growing in south Spain