Intermediate Topic 634 of 1102 Inorganic Chemistry
Borax
Sodium tetraborate decahydrate, used in glass, ceramics and cleaning.
In-depth explanation of Borax
Borax is sodium tetraborate decahydrate, Na2B4O7 x 10H2O, a white mineral mined from dry lake deposits. In water it hydrolyses to boric acid and borate ions, so its solutions are mildly alkaline, with a pH near 9. As a mild alkali and a flux, it is used in borosilicate glass, ceramic glazes, enamels, detergents and fire retardants. In the borax bead test, molten borax dissolves metal oxides to form coloured metaborate complexes, and cobalt gives a deep blue bead. It is of low toxicity but should still be handled with care.
Going deeper: Borax
Key ideas: Na2B4O7.10H2O really contains the tetraborate anion [B4O5(OH)4]2-. Aqueous solution is basic. Heating loses water, then fuses to a glassy mass of Na2B4O7 and B2O3; the borax bead test shows colors with metal oxides: Cu blue (oxidizing flame), Fe yellow-brown, Cr green, Co deep blue, Mn violet. Boric acid B(OH)3 is a weak Lewis acid, not proton donor: B(OH)3 + H2O gives B(OH)4- + H+.
Common mistakes and connections: Boric acid is monobasic, not tribasic, despite three OH groups. Students mix up borax formula with Na2B4O7 only, ignoring water. Bead test uses metaborate formation: Na2B4O7 gives 2NaBO2 + B2O3. Links to qualitative analysis, Lewis acid-base theory and glass making.
Visualization of Borax
Borax hydrolyses to boric acid and borate, giving a mildly alkaline solution near pH 9, between neutral water and a strong base. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Heating borax with a little cobalt oxide on a platinum loop gives a deep blue bead.
Frequently asked questions about Borax
What is Borax?
Sodium tetraborate decahydrate, used in glass, ceramics and cleaning.
Is Borax a beginner, intermediate or advanced topic?
Borax is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Borax?
Study these earlier topics in Inorganic Chemistry first: Cement, Magnesium Chemistry, Boron Family.
What comes after Borax?
The next topics in Inorganic Chemistry are Boranes and Aluminium Chemistry.
Can I practise Borax with quizzes?
Yes. The interactive lesson includes a self-check question on Borax, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Borax fits in Inorganic Chemistry
Borax is topic 19 of 113 in Inorganic Chemistry.