Question

When orthoboric acid is heated to red hot, the residue is (1) boron trioxide (2) boric acid (3) pyroboric acid (4) metaboric acid

Short answer

Boron trioxide (B₂O₃)

Step-by-step solution

Identify the compound being heated

The compound being heated is orthoboric acid.

Understand the heating process

Heating orthoboric acid to red hot involves a significant increase in temperature.

Chemical reaction of heating orthoboric acid

When orthoboric acid (H₃BO₃) is heated to red hot, it undergoes a decomposition reaction.

Identify the decomposition product

The decomposition of orthoboric acid at high temperatures results in the formation of boron trioxide (B₂O₃).

Confirm the correct answer

Thus, the residue left after heating orthoboric acid to red hot is boron trioxide.

Key concepts

boron trioxide formation

When orthoboric acid is heated to a red-hot temperature, it undergoes a chemical decomposition.
The product of this decomposition process is boron trioxide (B₂O₃).
Orthoboric acid has the chemical formula H₃BO₃. When it is heated, it loses water molecules, resulting in the formation of boron trioxide.
The chemical equation for this process is: H₃BO₃ → B₂O₃ + 3H₂O Here, three molecules of water (H₂O) are released for every two molecules of orthoboric acid that decompose.
Boron trioxide is a white, glassy solid that is often used in glass and ceramics industries.

chemical decomposition

Chemical decomposition is a process where a single compound breaks down into two or more simpler substances.
This can be driven by various factors such as heat, light, or a chemical reaction.
In the case of heating orthoboric acid, the compound is broken down by the application of heat.
This decomposition occurs because the bonds in the orthoboric acid molecule are weakened by the thermal energy.
Gradually, the compound loses its water of crystallization (water molecules that are part of its structure), resulting in a new substance.

heating process in chemistry

Heating in chemistry is often used to initiate reactions that would not occur at room temperature.
In this context, heating orthoboric acid results in its decomposition into boron trioxide and water.
The 'red hot' temperature refers to a very high heat level that is enough to cause such chemical changes.
The temperature necessary for this reaction is typically above 300°C.
This indicates that thermal energy is an essential factor in driving endothermic reactions, which require the intake of heat to occur.

orthoboric acid properties

Orthoboric acid, also known simply as boric acid, is a weak monobasic Lewis acid of boron.
It is often found as a white powder or colorless crystals, and is soluble in water.
This compound has various uses such as in antiseptics, insecticides, and as a flame retardant.
Moreover, orthoboric acid has a triclinic crystalline structure, which means its crystals are shaped in a specific geometric form.
When it is heated, it undergoes a phase transition from solid to a glassy state before decomposing into boron trioxide.
Its ability to decompose into boron trioxide when heated makes it valuable in materials science and chemistry fields.