Question

Borax on heating strongly above its melting point melts to a liquid, which then solidifies to a transparent mass commonly known as borax-bead. The transparent glassy mass consists of : (1) sodium pyroborate (2) boric anhydride (3) sodium meta-borate (4) boric anhydride and sodium metaborate

Short answer

The transparent glassy mass consists of (4) boric anhydride and sodium metaborate.

Step-by-step solution

Identify the Chemical Composition

When borax (Na2B4O7·10H2O) is heated, it loses water molecules initially and then proceeds to decompose.

Decomposition Process

Upon further heating, the borax decomposes into sodium metaborate (NaBO2) and boric anhydride (B2O3).

Forming the Borax Bead

The resulting transparent mass, known as borax bead, is a combination of these two compounds: sodium metaborate and boric anhydride.

Describe the Composition

The transparent glassy mass is thus composed of both sodium metaborate and boric anhydride.

Key concepts

Sodium Metaborate

Sodium metaborate is a compound that forms when borax is heated and loses water. Chemically, it is denoted as NaBO2.
This substance is an essential part of the borax bead.
It’s created in the decomposition process of borax.
When you heat borax, it first loses its water molecules.
Further heating causes it to break down into sodium metaborate and another compound.
This process of losing water and breaking down is called decomposition.
Sodium metaborate has several practical uses including glass production and as a reagent in chemical labs.

Boric Anhydride

Another key compound formed during borax decomposition is boric anhydride.
This is expressed chemically as B2O3.
Boric anhydride emerges alongside sodium metaborate when borax undergoes heating.
It's interesting to note that boric anhydride, like sodium metaborate, comes into existence because borax decomposes.
Beyond forming a part of the borax bead, boric anhydride plays significant roles in other places.
It's used in the production of borosilicate glass and as a fluxing agent in ceramics.
Both sodium metaborate and boric anhydride together form the transparent glassy mass.

Chemical Composition

Understanding the chemical composition of the borax bead is important to grasp the whole process.
Essentially, borax (Na2B4O7·10H2O) is a complex compound composed of sodium, boron, and water molecules.
When you heat borax, it initially loses water molecules which is a part of the first step of decomposition.
Further heating, it results in simpler compounds.
This leads to the formation of sodium metaborate (NaBO2) and boric anhydride (B2O3).
This is why the bead that forms is a clear, glassy mass containing these two compounds.
Combining both sodium metaborate and boric anhydride gives us a detailed understanding of the bead.
Knowing this helps in understanding and predicting the behavior of similar compounds in different scenarios.