Sodium – Properties and Applications

Chemical Formula

Na

Topics Covered

Background

Sodium carbonate or soda (Na₂CO₃) was the most popular sodium compound in ancient times. Soda was called as natron by the Egyptians and later, the Romans used a similar name for it, natrium which explains the origins of its chemical symbol Na.

Sodium had its origins from an Arabic word Suda, which means headache as soda was used sometimes to cure headaches. In Latin, the word suda became sodanum and hence the name sodium evolved.

In the early 1800s, Davy discovered a way of extracting active elements from their compounds. In 1807, he prepared sodium by the electrolysis of caustic soda (NaOH).

Basic Information

The basic information about sodium is listed in the table 1.

Table 1. Basic Properties of sodium

Key Properties

The key properties of sodium are:

• It is highly reactive, reacting explosively with water
• It is a silver-white metal having a waxy appearance
• It is soft with a bright shiny surface, however as sodium reacts with oxygen in the air it becomes dull due to the formation of a sodium oxide (Na₂O) film
• The density of sodium is slightly less than water
• It is a good conductor of electricity
• It reacts with oxygen at room temperature
• On heating, it combusts very rapidly, burning with a brilliant golden-yellow flame
• It reacts with acids to produce hydrogen gas
• It dissolves in mercury forming a sodium amalgam

Occurrence

Sodium cannot be found as a free element in nature. It is highly active especially with water and oxygen, hence always occurs as part of a compound. The most common sodium source in the Earth is halite.

Halite is almost pure sodium chloride (NaCl) and is also known as rock salt. Halite can be found in underground deposits, which formed when ancient oceans evaporated leaving sodium chloride as well as dry lake beds with large deposits located the USA, United Kingdom, France, Germany, China and India.

Isotopes

Sodium-23 is the only naturally occurring isotope of sodium.

Although six radioactive isotopes of sodium exist, only two have any commercial significance. These are described below:

• Sodium 22 and sodium 24 are two radioactive isotopes of sodium, which are used in medical applications. Sodium 24 is used as an electrolyte tracer to follow the path sodium takes in a person’s body to see if their uptake levels are within normal ranges, while sodium 22 is used in nuclear medicine imaging for positron emission tomography.
• Sodium -24 can also be used in non-medical applications. For instance, it is used for leak testing in industrial pipelines. Due to the limited penetrating power of the sodium radiation, detectors are only able to detect the radioactive sodium at leak points. Sodium 24 is also suited to this application due to its short half-life of just 15 hours.

Production of Sodium

Sodium metal is produced by the electrolysis of a mixture of sodium chloride and calcium chloride (CaCl₂) using the Down’s Process. The calcium carbonate is added to bring down the melting point of the mixture to about 600°C.

When an electric current is passed through the molten mixture, the NaCl decomposes with sodium being attracted to the cathode. It rises to the surface due to its low density and can be tapped off. Although calcium is also produced, it does not mix with the sodium due its much higher density of 2.54g/cc.

Health Aspects

Sodium has several important functions is humans, animals and plants. In humans, sodium controls the amount of fluid present in the cells. A lack or an excess of sodium can result in cells gaining or losing water. The occurrence of any of these changes can prevent the cells from performing their normal functions.

A number of sodium compounds are hazardous as carcinogens and as toxins in animals and plants. At the same time it is impossible to live without many of the compounds made of sodium.

Applications

The applications of sodium include:

• It is occasionally used as a heat exchange medium in nuclear power plants. Liquid sodium is sealed into pipes surrounding the reactor core. Generated heat is absorbed by sodium and forced through the pipes in a heat exchanger which can be used to generate electricity.
• Sodium is used in making metals such as titanium. Sodium is made to react with titanium tetrachloride (TiCl₄) to yield titanium.
• Sodium is used as a catalyst to make artificial rubber.
• An electric current and sodium vapor combine to form a yellowish glow. This principle is used for the making of sodium vapor lamps.
  • High pressure sodium vapor lamps use mercury that offers a natural color rendition of light
  • Low pressure sodium vapor lamps use a small amount of sodium along with neon, making the light both bright and economical

Source: AZoM.com