The Propertied of Sodium Chloride and Products Made From It - Essay Example

SALT AS A COMPOUND- PROPERTIES, MANUFACTURE AND USES Salt is a very common chemical compound used in our daily life. It has the chemical formula NaCland chemically the common salt that we use is called sodium chloride. It is very important in our daily life as a major content of our diet and it has many properties related to the proper physiological functions. Salt has a complex chemical behavior and it has its own unique properties and functions. Its manufacture is yet another complex process. The uses of salt are far more than our knowledge. It would be interesting to know the history of salt before getting into all these. Let us consider each of these aspects in a detailed manner. History: Salt was used even before the pre-historic period. Animals used to get salt from the various sources in nature and primitive man got his requirement of salt from animal meat. When he turned a cultivator, he found that some salt sources (like sea water) gave his vegetables the salty taste that he used to get on meat (as cited in http://www.saltsense.co.uk/history01.htm). Later on he learned how salt helped to preserve meat, cure hides and heal wounds. About 4,700 years ago, the Chinese Png-tzao-kan-mu, one of the earliest known writings recorded more than 40 types of salt (as cited in http://www.saltsense.co.uk/history02.htm). In the British aisles, there have been traces of inland brines from where ancient man made salt. Archaeological evidence is leading to Bronze Age to this age old practice. “We even know the names of a few of the Roman saltmakers. These are inscribed on some of the lead pans - Viventius, Veluvius and Cunitus. Complete Roman salt pans are in the Salt Museum and at Nantwich Museum. The leaden pans were roughly 90-100cm square by 15cm deep.Roman soldiers were partly paid in salt. It is said to be from this that we get the word soldier - sal dare, meaning to give salt. From the same source we get the word salary, salarium” (as cited in http://www.saltsense.co.uk/history04.htm). Distribution: “Salt is widely distributed in nature. It is found in solution in ocean water in concentrations of about 30 g/liter (about 4.08 oz/gallons) of water, meaning that salt makes up about 3 percent of ocean water by weight. The compound is also distributed throughout many rivers and inland lakes and seas, the concentration varying from 0.002 percent in Mississipi River to 12 percent in the Great Salt Lake. Salt can occur as a surface crust or layer in swamps and dry lake bottoms, especially in extremely arid regions. The mineral halite, more commonly known as rock salt or massive salt, occurs in beds deposited by the dehydration of ancient bodies of salt water. The compound is constantly being formed by the action of rivers and streams on rocks containing chlorides and compounds of sodium.” (as cited in http://encarta.msn.com/encyclopedia_761574334/Salt_(compound).html) Physical properties of NaCl: “Salt, also known as sodium chloride, is a chemical compound that has the formula NaCl. The term salt is also applied to the substances produced by the reaction of an acid with a base, known as a neutralization reaction. Salts are characterized by ionic bonds, relatively high melting points, electrical conductivity when melted or when in solution, and a crystalline structure when in the solid state.Salt is a white solid, soluble in hot or cold water, slightly soluble in alcohol, but insoluble in concentrated hydrochloric acid. In the crystalline form the compound is transparent and colorless, shining with an ice like luster. Under a microscope, salt appears in the structure of a cube. The compound usually includes traces of magnesium chloride (MgCl2), magnesium sulfate (MgSO 4), calcium sulfate (CaSO4), potassium chloride (KCl), and magnesium bromide (MgBr2). Salt melts at 804° C (1479° F) and begins to vaporize at temperatures just slightly above this; it has a specific gravity of 2.17” (as cited in http://encarta.msn.com/encyclopedia_761574334/Salt_(compound).html) Chemical properties of salt: Salt dissolves in water to form Na+ and Cl – ions and it forms a good electrolyte. The reaction of sodium chloride with acid gives the corresponding salt of sodium and it frees the Cl – ion. No reaction occurs between two salts. Salt reacting with base gives the corresponding salt and water molecule (Science for class 10, NCERT) Manufacture of salt: “Salt is currently mass produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. Later, this salt is purified and refined for further use” (as cited in http://en.wikipedia.org/wiki/Sodium_chloride). Uses of Salt: 1) BIOLOGICAL USES a) as a food content: Any prepared food item contains iodized salt. This salt content is very important for many physiological functions. The functions like sodium potassium transport mechanism, blood pressure maintenance etc are carried about by the dissociation of NaCl to sodium and chlorine ions. It is mandatory to use iodized salt to assure the function of thyroid gland and avoid goiter. Similarly, the excess usage of common salt can cause hypertension or commonly called the high blood pressure and less content of salt in blood can cause hypotension or low blood pressure. Both are dangerous conditions. “More recently, it was demonstrated to attenuate nitric oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium”(as cited in http://en.wikipedia.org/wiki/Sodium_chloride ) Salt is also used to preserve food as it has the capacity to absorb water content from food substance. Microorganisms die in salt solution due to osmosis occurring in their cell in the high density salt solution .Thus in effect high salt content prevent food decay. Pickles, sausages, dry fish etc use this property of salt. b) Other functions: Although salt is toxic to many of the land plants, salt is added to the soil with high basic property to neutralize the basicity of soil. Salt is used to detach leeches that have attached on the body for feeding themselves. Salt can even kill snails. It is used to disinfect wounds (as cited in http://en.wikipedia.org/wiki/Sodium_chloride). Salt is used to melt the snow on heavy snow covered lands. Salt is a good tooth powder which can effectively fight tooth decay. Wiping home appliances with salt solution can fight ants. 2) SYNTHETIC USES “Sodium chloride is also the raw material used to produce chlorine which itself is required for the production of many modern materials including PVC and pesticides. Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas gas and sodium hydroxide, according to the chemical equation 2NaCl + 2H2O → Cl2 + H2 + 2NaOH Sodium metal is produced commercially through the electrolysis of liquid sodium chloride. This is now done in a Down’s cell in which sodium chloride is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is more electropositive than sodium, no calcium will be formed at the cathode. This method is less expensive than the previous method of electrolyzing sodium hydroxide. Sodium chloride is used in other chemical processes for the large-scale production of compounds containing sodium or chlorine. In the Solvay process, sodium chloride is used for producing sodium carbonate and calcium chloride. In the Mannheim process and in the Hargreave’s process, it is used for the production of sodium sulfate and hydrochloric acid” (as cited in http://en.wikipedia.org/wiki/Sodium_chloride). 3) OPTICAL USES “Pure NaCl crystal is an optical compound with a wide transmission range from 200 nm to 20 um. It was often used in the infrared spectrum range and it is still used sometimes.NaCl crystal is soft, hygroscopic and inexpensive. This limits its application to protected environment or for short term uses (prototyping). Exposed to free air, NaCl optics will "rot".Today tougher crystals like ZnSe are used instead of NaCl (for the IR spectral range)” (as cited in http://en.wikipedia.org/wiki/Sodium_chloride) 4)CHEMICAL USES Common salt is used in the production of toilet soaps in the chemical industry (Butler, Poucher). It is an active ingredient in many cosmetics. It is used as a de-hydrating agent in aviation fuel. Its bio-chemical properties have been discussed earlier and they are numerous. Salt is used in most common chemical used in the household. The functions of common salt or sodium chloride don’t end with these few pages. It is an active ingredient in countless reactions some of which are not even considered a chemical reaction. Its functions are nothing but uncountable. No wonder in the idiom ‘you are the salt of my life’. Without salt everything appears vague and this is all about the strength and significance of salt. Reference: Chemistry Part 1 for class 12.Published by NCERT, India. Unit 1 G D Twigg - History of salt cited November 2002 . Accessed on 23rd March , 2009.Available at http://www.saltsense.co.uk/history04.htm http://www.saltsense.co.uk/history02.htm http://www.saltsense.co.uk/history01.htm Hilda Butler, William Arthur poucher. Pouchers Perfumes, Cosmetics and Soaps.published in 1923. Peyyeti Raja Kumar, Shivkumar, Shweta Upal et al. Science for class 10.published by NCERT, India.Chapter 2, 3 Salt.Accessed on 23rd March, 2009.Available at http://en.wikipedia.org/wiki/Salt Salt(compound).Accessed on 23rd March 23, 2009.Available at URL http://encarta.msn.com/encyclopedia_761574334/Salt_(compound).html) Read More