Sodium

Sodium (Na) is indeed a key element in the alkali metal group (Group 1 [Ia]) of the periodic table. It is characterised by its silvery-white appearance and exceptional softness, making it easy to cut with a knife. Due to its high reactivity, sodium is not found in its elemental form in nature. Instead, it primarily exists in various compounds, the most notable being sodium chloride (NaCl) or table salt.

1.0Introduction

Sodium is Earth's sixth most common element, making up about 2.6% of the crust. It is mainly found as sodium chloride (NaCl), a soluble compound accumulated in oceans and salt beds. 

Sodium is a soft, explosive, silvery-white metal named after the English word “soda.” Its compounds are widely used daily, the most familiar being table salt (sodium chloride, NaCl). As one of the most reactive metals in the periodic table, sodium readily forms compounds with other elements. It is essential in biological processes, like fluid regulation and nerve function, and is widely used in industries for water softening and chemical production.

2.0Physical Properties of Sodium

• Appearance: Sodium is a soft, silvery metal with a strong metallic lustre, similar in colour to silver.
• Malleability: At room temperature, it is so soft that it can be shaped into thin sheets under finger pressure and easily sliced with a knife.
• Reactivity: Sodium tarnishes quickly when exposed to air, reacting with oxygen to form sodium oxide, which further reacts with water vapour to create a sodium hydroxide film. Due to its high reactivity, sodium is stored in oil or inert gas to prevent these reactions.
• Conductivity: With just one electron in its outermost shell, sodium has weak bonding, allowing the electron to move freely. This gives sodium high thermal and electrical conductivity.
• Flame Test: Sodium and its compounds produce a bright yellow flame in a flame test due to the emission of light with a wavelength of 589.6 nm, caused by the decay of excited 3s electrons to the 3p state.

3.0Chemical Properties of Sodium

• Reaction with Water: Sodium reacts with cold water, resulting in the production of hydrogen gas and a colourless sodium hydroxide solution:    

    2Na+2H2O→2NaOH+H2

• Reaction with Oxygen: When sodium is exposed to oxygen, it forms sodium oxide and sodium peroxide, accompanied by an orange flame that cools to a white solid:

Sodium Oxide: 4Na+O2→2Na2O

Sodium Peroxide: 2Na+O2→Na2O2​

• Reaction with Alcohol: Sodium reacts with anhydrous alcohols to produce the corresponding alkoxides: Na+ROH→RONa+12H₂​This reaction is particularly vigorous with methanol and becomes less intense with larger alcohols.
• Reaction with Haloalkanes: The formation of sodium halides is energetically favoured, facilitating the Wurtz reaction, which is used in organic synthesis:2RCl+2Na→R―R+2NaCl

For instance, octane can be synthesised from bromobutane and sodium.

4.0Compounds of Sodium 

1. Sodium Carbonate (Washing Soda) - Na₂CO₃·10H₂O

Preparation: Sodium carbonate is produced via the Solvay Process, where sodium chloride reacts with ammonium bicarbonate:

2NaCl+NH₃+CO₂+2H₂O→Na₂CO₃+2NH₄Cl₂ 

Ammonium chloride is treated with calcium hydroxide to recover ammonia:

2NH₄Cl+Ca(OH)₂→2NH₃+CaCl₂+2H₂O

Properties: Sodium carbonate is a white crystalline solid (washing soda), highly soluble in water. It undergoes thermal changes:

Decahydrate to monohydrate:Na₂CO₃⋅10H₂O→Na₂CO₃⋅H₂O+9H₂O

Monohydrate to anhydrous soda ash:Na₂CO₃⋅H₂O→Na₂CO₃+H₂O

Uses:

• Water softening and cleaning.
• Production of glass, soap, and caustic soda.
• Applications in paper, paint, and textiles.
• Laboratory reagent for analysis.

2. Sodium Chloride

• Source: Sodium chloride mainly comes from seawater containing 2.7% to 2.9% sodium chloride. In tropical countries like India, it is harvested by solar evaporation, producing about 5 million tons annually.
• Purification: Crude sodium chloride from brine contains impurities like sodium sulfate, calcium chloride, and magnesium chloride. To purify, the crude salt is dissolved in minimal water, filtered, and saturated with hydrogen chloride gas to crystallise pure sodium chloride.

Key Properties:

• Melting Point: 1081 K
• Solubility: 36.0 g in 100 g of water at 273 K (solubility remains stable with temperature).

Uses:

Table salt for domestic use.

Production of sodium peroxide (Na₂O₂), sodium hydroxide (NaOH), and sodium carbonate (Na₂CO₃).

3. Sodium Hydroxide 

• Preparation: Sodium hydroxide is commercially produced by the electrolysis of sodium chloride in a Castner-Kellner cell. In this process, a brine solution is electrolysis with a mercury cathode and carbon anode, producing sodium amalgam at the cathode and chlorine gas at the anode. The amalgam is then treated with water to yield sodium hydroxide and hydrogen gas:

Na-amalgam+2H₂​O→2NaOH+2Hg+H₂​

• Properties: Sodium hydroxide is a white, translucent solid melts at 591 K and is highly soluble in water, forming a strong alkaline solution. The solid is deliquescent and reacts with atmospheric CO₂ to produce sodium carbonate (Na₂CO₃).

Uses:

• Manufacture of soap, paper, and various chemicals.
• Petroleum refining.
• Purification of bauxite.
• Mercerising cotton in textiles.
• Preparation of pure fats and oils.
• Laboratory reagent.

4. Sodium hydrogen carbonate (Baking Soda) - NaHCO₃

• Overview: Sodium hydrogen carbonate, commonly known as baking soda, decomposes upon heating to release carbon dioxide gas. This reaction creates bubbles that leave holes in baked goods, making them light and fluffy.
• Preparation: It is produced by saturating a sodium carbonate solution with carbon dioxide, resulting in the precipitation of this white crystalline powder due to its lower solubility:

Na₂CO₃+CO₂+H₂O→2NaHCO₃

Uses:

• Mild antiseptic for skin infections.
• Component in fire extinguishers.
• Sodium can also form organosodium compounds directly attached to carbon, such as methylsodium (NaCH₃):

Hg(CH₃)₂+2Na→2NaCH₃+Hg

• Reactions with halogenated hydrocarbons can be vigorous, sometimes resulting in explosions when combined with carbon tetrachloride.

5.0Uses of Sodium

• Sodium is used in the production of soaps.
• It aids in the purification of molten metals.
• Sodium is utilised in sodium vapour lamps for street lighting.
• It is a key component of sodium chloride and is essential for life.
• Sodium is vital for producing organic compounds and forming esters.
• Solid sodium carbonate is necessary for making glass.