Sodium Borate: Borax, Preparation, Structure and Uses

Sodium borate, also known as borax, is a solid boron compound which appears in an amorphous or crystalline state. It consists of 3 positively charged ions and a borate ion. It is commonly found in seasonal lakes and goes by the chemical formula Na₂B₄O₇.10H₂O. Borax is extensively used in different fields in our day to day lives. We are highly dependent on it for cleaning agents, pesticides, food preservatives and fire retardent.

Keyterms: Sodium, Borate, Borax, Boron, crystalline state, pesticides,  food preservatives, fire retardent, Boric acid

Read more: Ionic Radius 

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What is Sodium Borate?

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Sodium borate is a crucial boron compound which also goes by the name sodium tetraborate, or disodium tetraborate. Another popular name of sodium borate is borax. In its powdered form, it appears as a white colour, with a composition of fragile colorless crystals. These crystals are water soluble and besides being a boron compound, sodium borate is also a mineral, and plays the role of a salt of boric acid. 

The word borax indicates octahydrate. It states that borax is a couple of chemical compounds, which are similar in nature but differ in their crystal water content. The borax, which we find in the market places and local stores, is in a partial dehydration state. 

Sodium borate helps regulate the spread of fire by acting as a fire retardant. Borax is also used by minors in order to extract gold mines. This process is called borax method and helps flush out the traces of harmful mercury present in the gold mines. It also serves as an antifungal compound and is used in making buffer solutions. The use of borax around us is neverending.

Borax in crystalline form 

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Occurrence of Sodium Borate

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Sodium borate has the tendency to occur naturally in seasonal lakes. It occurs in the form of evaporite deposits, which happens because the lakes are exposed to a constant evaporation process. 

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Chemical Formula & Structure of Sodium Borate

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The IUPAC name of sodium borate is given as sodium tetraborate decahydrate. IUPAC stands for International Union of Pure and Applied Chemistry.

There is no denying the fact that sodium borate exists in two different forms. Each of them is unique and serves an important role in Chemistry.

One state is the hydrated form, where the water of hydration seems to be active. The chemical formula of borax here is Na₂B₄O₇.10H₂O. In the dehydrated state of sodium borate, water of hydration is absent. Its chemical formula is Na₂B₄O₇

The shape of this compound is a trigonal and its molecular weight happens to be 381.4 g/mol(hydrated state). 

In the structure, you can see three ions charged positively, and are attracted towards the borate ion. Due to this force, they form into ionic bonds. 

As we already know borate is a covalent compound of boron and oxygen, it fuses into forming boron oxyanion. It can also be concluded that the structure is tetrahedral in shape. 

Read more: Oxoacids of Sulphur

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Properties of Sodium Borate

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1. Physical Properties

• The molecular weight of sodium tetraborate in the hydrated state is 381.38 g/mol, where in dehydrated form, it measures about 201.22 g/mol.
• The boiling point of sodium borate is 1,575^o.
• The melting point of sodium borate is 743^o.
• Borax is easily soluble in water.
• The density of sodium borate is 1.73 g/dm³.
• Sodium borate is white in colour, and can occur as a crystalline or amorphous substance.

2. Chemical Properties

• Sodium borate has a stable nature. Borax does not cause any corrosion when present near glass.
• Borax doesn't go well with moisture, and it is also incompatible with alkaloidal salts, mercuric chloride, zinc sulfate and other metallic salts.
• When present in the hydrated form, borax reacts with acids to a great extent. Boric acid is formed when the compound reacts with acids.
• When it comes down to ethylene glycol, borax has a high solubility. 
• Sodium borate is flammable in nature. When sodium borate is burned, a greenish flame with a tint of yellow can be observed. 
• It is sparingly soluble in acetone and reacts with bases.

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Preparation Method Of Sodium Borate

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1. Ca₂B₆O₁₁ + 2Na₂CO₃ → Heat→ Na₂B₄O₇ + 2NaBO₂ + 2CaCO₃↓

Sodium carbonate, upon coming in contact with colemanite, reacts heavily. Colemanite is a borate mineral by nature. When this reaction occurs, in the presence of heat, sodium borate and calcium carbonate is formed. 

2. 4H₃BO₃ + Na₂CO₃ → Na₂B₄O₇ + 6H₂O +CO₂ ↑

Sodium metaborate and carbon dioxide react together in order to give rise to sodium borate.

3. 4NaBO₂ + CO₂ → Na₂B₄O₇ + Na₂CO₃

When boric acid reacts with sodium carbonate, three byproducts are formed. These are sodium carbonate, water, and carbon dioxide. 

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Reactions of Sodium Borate

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1. Na₂B₄O₇ + 7H₂O → 4Na[B(OH)₄]

When amorphous borax Na₂B₄O₇ reacts with concentrated sodium hydroxide solution, tetrahydroborate is formed. 

2. Na₂B₄O₇ + 2NaOH → 4NaBO₂ + H₂O (At a high temperature of around 700-750 degrees)

The fusion of sodium borate ultimately gives rise to sodium metaborate.

3. Na₂B₄O₇ + 2NaOH + 4H₂O₂ + 11H₂O → 2Na₂[B₂(O₂)₂ (OH)₄].6H₂O

Sodium borate reacts with hydrogen peroxide and gives peroxoborate as a result. 

4. Na₂[B₄O₅(OH)₄]. 8H₂O → 2Na⁺ + B₄O₅(OH)₄^2- + 8H₂O (l)

2Na + 2Na⁺ + B₄O₅(OH)₄^2- + 5H₂O → 2Na⁺(aq) + 4B(OH)₃ + 2OH^-

2Na⁺ + B₄O₅(OH)₄^2- +2HCl + 5H₂O → 4B(OH)₃ + 2Na⁺ + Cl^-

When sodium borate dissolves in water, it dissociates completely. After this it starts hydrolyzing into orthoboric acid hydroxyl ions. This ultimately leads to a basic solution. It can be concluded that borax reacts with strong acid solutions.

Read more : Sulphuric Acid 

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Uses of Borax

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• Borax is a common household product when it comes to cleaning and laundry. It is also a general component present in some soaps. Dentists are also dependent upon borax for carrying out tooth whitening formulas. 
• In chemical laboratories, Borax is often used to make buffers in the form of boric acid. It is also used in dimethyl pimelimidate as a solution.
• Borax is also used as a food preservative, to enhance its taste and appearance. It also keeps the food in a firm structure.
• Some countries like the Philippines are using borax as a means of extracting gold in small-scale mining facilities. This is also popularly being called the borax method.
• Borax also acts as a water softening agent, and is used in many treatment plants. 
• Borax is an important component of slime and serves as a co-complexing agent.

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Harmful Effects of Sodium Borate

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• A significant dosage of sodium borate can cause harmful effects like severe symptoms, and even death of a person.
• Exposure to borax for a longer period of time can lead to irritation of the respiratory tracts.
• Intake of this compound can cause nausea, consistent vomiting, diarrhoea, and abdominal pain.
• Affects the nervous system causing headaches and fatigue.
• Can cause rashes on palms, soles and private parts of the body.
• High consumption of borax can lead to liver cancer over the years.

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Points to Remember 

• Sodium borate is a colorless chemical compound. It is also called borax and sodium tetrahydrate. It was first discovered in dry lake beds in Tibet, in the 8t century. Borax heavily reacts with acids and serves many purposes.
• The occurrence of sodium borate in nature is in the form of deposits in seasonal lakes. This happens because of the lakes being subjected to longer periods of evaporation.
• Borax occurs in two forms : hydrated and dehydrated. The chemical formula of borax in the hydrated form is Na₂B₄O₇.10H₂O while it is Na₂B₄O₇ in the dehydrated form.
• Sodium borate is white in colour and dissolves easily in water. It is stable and also shows high solubility towards ethylene glycol. The molecular weight of the hydrated state of borax is 381.38 g/mol whereas on the other hand it is 201.22 g/mol in its dehydrated state. Borax forms a greenish yellow flame when burned. 
• Sodium borate is an important component in some cosmetics products, acts as a cleaning agent, used in swimming pools to control the pH levels of water, food preservative, teeth whitening process, and also as a woodwork treatment. It also acts as a curing agent for snake skins and helps extract gold in some places. 

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