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What is Sodium Borate?

Sodium borate is a white solid boron compound, composed of borate ion and sodium ion.  It can be in a crystalline or amorphous state. Sodium borate is a mineral, which naturally occurs in the earth’s crust. It is also known as Borax. The most important boron compounds are sodium tetraborate, disodium tetraborate, and Borax. 

Occurrence of Sodium Borate

Sodium borate naturally occurs in seasonal lakes as a deposit due to evaporation. Sodium borate is commonly found in California, Tibet, Romania, southwestern United States and Turkey, etc. 

Chemical Formula of Sodium Borate

Sodium borate exists in two states, hydrated form, and dehydrated form. Hydrated forms of sodium borate are the states in which the water of hydration is present, while in dehydrated forms of sodium borate there is no water of hydration present. The chemical formula of sodium borate in the hydrated state is Na2B4O7.10H2O and in the dehydrated state is Na2B407. Its molecular weight is 381.4 g/mol. The International Union of Pure and Applied Chemistry (IUPAC) name of sodium borate is sodium tetraborate decahydrate.

Structure of Sodium Borate

In sodium borate structure three positively charged sodium ions are attracted by the negatively charged borate ion. They form ionic bonds. Borate is a covalent compound of boron and oxygen that forms boron oxyanion. Its shape can be trigonal or tetrahedral.

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Properties of Sodium Borate

  1. Physical Properties of Sodium Borate

  • The molecular weight or molar mass of dehydrated sodium borate is 201.22 g/mol, while that of hydrated form is 381.38 g/mol.

  • The colour of sodium borate is white and it can be in a crystalline or amorphous state.

  • The density of sodium borate is 1.73 g/dm3.

  • The boiling point of sodium borate is 1,575℃.

  • The melting point of sodium borate is 743℃.

  • Sodium borate is soluble in water.

  1. Chemical Properties of Sodium Borate

  • The hydrated form of sodium borate is highly reactive with acids. On reacting with acids, sodium borate forms boric acid. 

  • Sodium borate is a  flammable compound. It produces a greenish-yellow flame when burned.

  • It shows very high solubility towards ethylene glycol.

  • It is sparingly soluble in acetone.

  • It shows reactivity with bases.

Preparation Method Of Sodium Borate

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

Colemanite is a borate mineral, which in reaction with sodium carbonate in the presence of heat forms sodium borate and calcium carbonate.

2. 4NaBO2 + CO2 → Na2B4O7 + Na2CO3

Sodium metaborate on reaction with carbon dioxide leads to the formation of sodium borate.

3. 4H3BO3 + Na2CO3 →Na2B4O7 + 6H2O +CO2

Boric acid on reacting with sodium carbonate forms sodium borate and water and carbon dioxide are formed as byproducts.

Reactions of Sodium Borate

1. Na2B4O7 + 7H2O → 4Na[B(OH)4]

Amorphous borax Na2B4O7 forms tetrahydroxoborate on reacting with concentrated sodium hydroxide solution.

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

The fusion of sodium borate leads to the formation of sodium metaborate.

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

When sodium borate reacts with hydrogen peroxide it forms peroxoborate.

4. Na2[B4O5(OH)4]. 8H20 → 2Na+ +B4O5(OH)42- + 8H20 (l)

2Na + 2Na+ + B4O5(OH)42- +5H2O⇌2Na+(aq) + 4B(OH)3 + 2OH- 

2Na+ + B4O5(OH)42- +2HCl +5H20 → 4B(OH)3 +2Na+ + Cl-

Sodium borate, when dissolved in water, dissociates completely, and then, hydrolyzes to orthoboric acid hydroxyl ions, which leads to the basic solution. Therefore, borax reacts with strong acid solutions. 

Uses of Sodium Borate

  • It is used as a buffer in various reactions.

  • A 10 per cent solution of sodium borate is used as an insect killer, for roach killing, and as a moth-preventative. 

  • It can also be used as fungicide and herbicide.

  • In many industries and treatment plants, it is used as a water softening agent.

  • It is used as a food additive as a preservative.

Is Sodium Borate Safe?

Sodium borate is not acutely toxic, which means at low amounts or at low concentration it does not show any harmful effects, but when it is inhaled or ingested in large amounts it would have harmful effects on health. As far as pesticides go, it is one of the safest chemical compounds available. A 2006 survey of the chemical by the U.S. The Environment Protection Act finds no signs of toxicity from exposure and no evidence of cell toxicity in humans. However, this does not make sodium borate categorically safe. Intake of large amounts of sodium borate can cause vomiting, nausea, and diarrhoea. While the findings are rather contradictory, it's advisable children and pregnant women limit their exposure to sodium borate if possible.

Harmful Effects of Sodium Borate

  • Organ system toxicity 

  • Fertility damage 

  • Damage to an unborn child 

  • Endocrine and hormone disruption 

  • Skin allergy 

  • Eye irritation

  • Damage to the male reproductive system 

  • Respiratory irritation 

Did You Know?

  • Most of the sodium borate is found in the United States. It comes from the seasonal lakes through the erosion process in the Mojave Desert in California.

  • Sodium borate is used in cosmetics, cleaning products and personal care products.

  • Sodium borate offers many health benefits like maintaining bone health, maintaining the hormonal balance, improving the nervous system and reducing inflammation.

  • Commercially sold borax is usually partially dehydrated.

  • Sodium borate is used as a fire retardant, as it has the ability to release water from its crystalline structure. 

FAQ (Frequently Asked Questions)

1. What is the IUPAC name of sodium borate?

Sodium tetraborate decahydrate is the IUPAC name of the sodium borate.

2. Name some of the borate minerals that naturally occur in the earth's crust.

Colemanite, kernite, boracite, painite are some borate minerals, which naturally occurs in the earth’s crust. This mineral is used for the formation of sodium borate.

3. Is sodium borate an ionic compound or covalent compound?

In the sodium borate structure, three positively charged sodium ions are electrostatically attracted by the negatively charged borate ion. These types of compounds are called ionic compounds.

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