Sodium (Na): Properties & Uses

Sodium is one of the most reactive elements on our planet, and its discovery was also done in the laboratory by British scientist Sir Humphry Davy in 1807 by performing electrolysis of caustic soda (NaOH). The name of sodium comes from the English word soda and latin sodanum for “headache remedy”.  Its symbol ‘Na’ comes from the Latin word natrium for “natron”, which also means a soda. It is the sixth most abundant element, which comprises 2.6% of earth’s crust. It is categorised under alkali metals with atomic number 11 in the periodic table.

Properties

Physical Properties

Sodium metal possesses silverish lustre at standard temperature and pressure range. It can be easily cut with a knife due to its soft nature.

 

Existence

As it is a highly reactive element, it is never found free in nature. It is usually found in form of compounds. The most common sodium compound is sodium chloride (NaCl), which is a soluble salt which is extracted from the oceans. It is also found in minerals, such as cryolite, zeolite and sodalite.

Melting and Boiling point

Sodium melts at a temperature of 98°C and boils at 883°C.

Flame Colour

In a flame test, sodium and its compounds impart yellow colour. This is the characteristic colour, which is used for the detection of sodium, and its concentration in the sample can be determined by flame photometry.

Isotopes

Although isotopes ranging from  ¹⁸Na to ³⁷Na are known, its only naturally occurring stable isotope is ²³Na. ²²Na and ²⁴Na are two stable radioisotopes with a half-life of about 2.6 years and 15 years respectively.

 

Chemical Properties

Reactivity towards Air

Sodium metal tarnishes in dry air due to the formation of its peroxide, which in turn reacts with moisture to form sodium hydroxide. It reacts vigorously when coming in contact with air. Therefore, it is usually kept in kerosene oil.

2Na(s) + O2(g)→ Na2O2 (sodium peroxide)

Reactivity towards Water

Sodium reacts rapidly with water to form its hydroxide and dihydrogen.

2Na(s) + 2H2O→ 2NaOH(aq) + H2(g) (sodium hydroxide)

It is an exothermic reaction.

 Sodium Compounds

 

The most important sodium compounds are Table salt (NaCl), Baking soda (NaHCO₃), Caustic soda (NaOH), Borax (Na₂B₄O₇• 10H₂O). Sodium usually forms ionic bonds to water and anions, in compounds, and it is viewed as a hard Lewis acid. Most soaps are sodium salts of fatty acids.

 

 

Aqueous solutions

Sodium forms water-soluble compounds, such as halides, sulfates, carbonates. Direct precipitation of sodium salts from aqueous solution is rare because sodium salts typically have a high affinity for water. Sodium salts are usually isolated as solids by evaporation or by precipitation with an organic antisolvent, such as ethanol because of the high solubility of its compounds.

Intermetallic compounds

Sodium forms alloys with many metals, such as potassium, calcium, lead, and group 11 and 12 elements. Sodium and potassium form KNa₂ and NaK. It is an excellent thermal and electrical conductor. Sodium also forms alloys with gold and silver. Group 12 metals are known to make alloys with sodium. Zinc, Cadmium and mercury also form alloys with sodium.

Uses

 Biological Role in Humans

Sodium is an essential mineral that regulates blood volume, blood pressure, and pH in the human body; however, a person can get high blood pressure by consuming too much sodium.

Dietary sources

Sodium chloride is the principal source of sodium in our diet, and is used as a preservative in pickles and jerky (lean trimmed meat); for Americans, most sodium chloride comes from processed foods. Sodium occurs naturally in some foods and is often added during manufacturing. Celery, beets and milk are a few of the foods where you’ll find them naturally. Packaged and prepared foods, like canned soups, lunch meats and frozen dinners, often have sodium added during manufacturing -either as salt or other common forms of sodium, like baking soda. It also comes from food additives such as sodium nitrite, baking soda(sodium bicarbonate), and sodium benzoate. Overall, more than 70 per cent of the sodium we eat comes from processed, prepackaged and restaurant foods. It’s much more difficult to limit sodium when it’s already added before it’s bought.

Sodium and Blood Pressure

Sodium attracts water, and a high-sodium diet draws water into the bloodstream, which can increase the volume of blood and subsequently your blood pressure. High blood pressure (also known as hypertension) is a condition in which blood pressure remains elevated over time. Uncontrolled high blood pressure can raise the risk of heart attack, heart failure, stroke, kidney disease, and blindness. In addition, blood pressure generally rises as you get older, so limiting your sodium intake becomes even more important each year.

 Sodium-Potassium Pump

Our bodies use a lot of energy. ATP(Adenosine triphosphate) is one of the major currencies of energy in our cells; it is continuously used and rebuilt throughout the day. This ATP is spent in many ways: to power muscles, to make sure that enzymes perform the proper reactions, to heat your body. The sodium-potassium pump is found in our cellular membranes where it is in charge of generating a gradient of ions. It continually pumps sodium ions out of the cell and potassium ions into the cell, powered by ATP. For each ATP that is broken down, it moves 3 sodium ions out and 2 potassium ions in. As the cell is depleted of sodium, this creates an electrical gradient and a concentration gradient, both of which are put to use for many tasks. The most important use of this gradient is in the transmission of nerve signals. The gradient also helps to control the osmotic pressure inside the cells, and powers a variety of other pumps that link the flow of sodium ions with the transport of other molecules, such as calcium ions or glucose.

Medicine for the heart

A traditional cure for heart failure works by blocking the sodium-potassium pump. Plant toxins like digitalis and ouabain and similar toxins from poisonous toads, collectively known as cardiotonic steroids, can be used in small doses to slow the pumping of ions. As the level of sodium ions builds up inside the cell, this slows the sodium-calcium exchanger, leading to a build-up of calcium, which ultimately increases the force of contraction of the heart muscle. Recent research has revealed that our own cells make molecules similar to these toxins, but only in low concentrations to regulate the action of our sodium-potassium pumps.

Sodium-Cooled Fast Reactors

As the world’s population continues to grow, the need to produce clean, safe and sustainable energy that meets basic electricity production and primary energy needs will continue to increase. Nuclear energy has the potential to become a prominent low-emission supplier. Nuclear Reactors (Generation 4) have the potential to serve as an opportunity to further develop the technology’s sustainability and efficiency. A Sodium-cooled Fast Reactor (SFR) is a type of nuclear reactor that utilizes molten sodium metal as the reactor coolant as it allows for a high power density with a low coolant volume. An SFR can achieve a core power density of around 300 MW/m3 compared with Pressurized Water Reactors (PWR) that achieve 100 MW/m3. Furthermore, a sealed coolant system is needed as the sodium is highly reactive with air and water; however, the oxygen-free system prevents corrosion. The primary sodium coolant does not directly exchange its heat with the water. Instead, a sodium-sodium heat exchanger is used where the secondary molten sodium stream can exchange its heat with water to generate steam. SFRs have the potential to become an attractive energy source for countries interested in managing their nuclear supply and nuclear waste.

 Industrial Applications

Sodium Methoxide is widely used reagent in industry and the laboratory. It is applicable to the synthesis of numerous compounds ranging from Pharmaceuticals to Agrichemicals. Sodium Methoxide is used as an initiator of anionic addition polymerization with ethylene oxide, forming a polyether with high molecular weight. Biodiesel (a form of diesel fuel derived from plants or animals) is prepared from vegetable oils and animal fats, that is, fatty acid triglycerides, by trans-esterification with methanol to give fatty acid methyl esters (FAMEs). This transformation is catalyzed by sodium methoxide.

 Washing Soda

Sodium carbonate (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na₂CO₃. All forms are white, water-soluble salts that yield moderately alkaline solutions in water. It was extracted historically from the ashes of plants growing in sodium-rich soils. Ashes of these sodium-rich plants were different from ashes of wood, that’s why sodium carbonate became known as ‘soda ash’. Some common application of washing soda include: 1) It is used as a cleansing agent for domestic purposes like washing clothes, 2) It is a component of many dry soap powders, 3) It is used for removing temporary and permanent hardness of water, 4) It is used in the manufacture of glass, soap and paper, 5) It is used in the manufacture of sodium compounds like borax.

 Sodium-Vapor lamp

A sodium-vapour lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589nm. There are two varieties of such lamps; High pressure and Low-pressure sodium lamps. Low-pressure sodium lamps (LPS) are highly efficient electrical light sources, but their yellow light restricts applications to outdoor lightings, such as street lamps, where they are widely used. High-pressure sodium lamps (HPS) emit a broader spectrum of light than the low-pressure lamps, but they still have poorer colour rendering than other types of lamps. Low-pressure sodium lamps only give monochromatic yellow light and so inhibit colour vision at night. They are used mainly for outdoor lighting (such as street lights and security lighting). The locations where light pollution is a consideration, such as near astronomical observatories or sea turtle nesting beaches, low-pressure sodium is preferred. High-pressure sodium (HPS) lamps have been widely used in industrial lighting, especially in large manufacturing facilities, and are commonly used as plant grow lights. They have also been widely used for outdoor area lightings, such as on roadways, parking lots, and security areas.