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Borax Formula – Structure, Properties, Uses, Sample Questions

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  • Last Updated : 24 Jun, 2022

Boron is a chemical element that exists in both crystalline and amorphous forms. It bears the symbol B and atomic number 5 with an atomic weight of 10.81amu. The amorphous form of Boron is powerful in form with brown color and in its crystalline state, it is shiny and dark. Turkey is the largest producer of Boron in the world.

Borax formula

Sodium borate or Sodium borate decahydrate or Sodium tetraborate decahydrate which is popularly known as Borax is widely known for it’s antifungal or fungus prevention usage.Borax is basically a hydrate salt of boric acid. Borax is generally referred to few crystals and has different chemical formulae depending upon the water of crystallization. Borax is has wide range of uses ,it is used as a co-complexing agent, fungicide and water softening agent.

Structure of Borax


Occurrence of Borax

Repeated evaporation in seasonal lakes leads to the natural occurrence of borax. It was first discovered in dry lake beds of Tibet and was imported to Arabian estates.

Preparation of Borax

Borax is prepared from colemanite (Ca2B6O11). The reaction involved is as follows,

Ca2B6O11 + 2Na2CO3 → (In the presence of heat)→ Na2B4O7 + 2NaBO2 + 2CaCO3↓(precipitate)

Further we need to treat NaBO2(Sodium metaborate) with carbon dioxide in order to convert it to borax and the reaction involved is as follows,

4NaBO2 + CO2 → Na2B4O7 + Na2CO3

Physical properties of Borax

  • Borax is a white crystalline solid compound.
  • The molar mass of Borax is 202.2 g/mol (anhydrous form) and 381.38 g/mol (decahydrate).
  • The density of Borax is 1.7 g/cm3 (decahydrate).
  • The refractive index of Borax is 1.472 (decahydrate).
  • The boiling point of Borax is 1,575°C (anhydrous).
  • The melting point of Borax is 743°C (anhydrous).

Chemical properties of Borax

  • Borax is ignitable or flammable and gives a yellowish-green flame.
  • Borax is a soluble compound with solubility in water at 31.7 g/L.
  • Borax has a high solubility in ethylene glycol and a low solubility in acetone.
  • Borax reacts with hydrochloric acid to form boric acid. The reaction involved is given as,  

Na2B4O7·10H2O + 2 HCl → 4 B(OH)3 + 2 NaCl + 5 H2O

  • Borax is highly soluble in ethylene glycol and sparingly soluble in acetone.

Uses of Borax

  1. Borax is used as a pest killer.
  2. Borax is a very good disinfectant.
  3. Borax is used as a food preservative.
  4. Borax is used in the preparation of buffer solutions.
  5. Borax is used as an alkalizer for pharmaceutic purposes.

Sample Questions

Question 1: List a few harmful effects of Borax?


  • Irritation in respiratory tracts is common due to continuous exposure to Borax.
  • Consumption of Borax in little quantity may also cause nausea, vomiting ,headache and rashes on palms.

Question 2: Explain the Co-complexing nature of Borax?


Borax is the source of borate ions which are very good at forming complex ions in water. Borate along with suitable polymer bed helps to chromatograph the non glycated hemoglobin distinctively from glycated hemoglobin.

Question 3: Differentiate Borax and Boric Acid?



Boric Acid

Borax is basically a hydrate salt of boric acid.Boric acid is a weak,monobasic Lewis acid of Boron.
It is also known as  Sodium borate or Sodium borate decahydrate or Sodium tetraborate decahydrate.It is aslo known as hydrogen borate, boracic acid, or orthoboric acid.

Question 4: What is the resulting product formed when Borax reacts with Sodium hydroxide?


Sodium tetrahydroxyborate is formed when Borax reacts with NaOH (Sodium hydroxide). The reaction involved is as follows,

Na2B4O7 + 7H2O + 2NaOH ⇢ 4Na[B(OH)4].

Question 5: List the various chemical formulae of Borax based on water of crystallization?




Anhydrous Sodium tetraborateNa2B4O7
Sodium tetraborate octahydrateNa2[B4O5(OH)4].8H2O
Sodium tetraborate pentahydrateNa2B4O7 . 5H2O

Question 6: Explain the water softening nature of Borax?


Hardness of water is mainly caused due to the Ca+2, Mg+2 cations. Borax reacts with these cations and forms precipitate which can be separated out easily and hence water becomes soft. The reaction involved in softening process is as follows:

Ca+2 (aq) + Na2B4O7 (aq) ⇢ Ca B4O7 (s)⇣ + 2 Na+ (aq) 

Mg+2 (aq) + Na2B4O7 (aq) ⇢ Mg B4O7 (s)⇣ + 2 Na+ (aq)

Question 7: List the safety measures to be followed while using borax to avoid risks?


  1. Always use Borax in a place where circulation of air is very good with proper ventilation.
  2. Always use gloves while handling Borax.
  3. Incase if Borax comes in contact with your skin or eyes,thoroughly wash them for 10 minutes.
  4. Washing hands after using Borax and avoid eating food or drinking without washing hands.
  5. Always contact doctor if situation gets out of control.
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