Question

Which of the following statements is false about boric acid? (1) Boron is in $s{p}^3$ hybridization. (2) It has layer structure in which planar ${\mathrm{BO}}_3$ units are linked by hydrogen bonding. (3) It can be used as solid lubricant as the layers are slippery. (4) Different layers are held by weak Van der Waal's forces.

Short answer

Statement 1 is false; boron is in sp2 hybridization, not sp3.

Step-by-step solution

Understand the Statements

There are four statements provided about boric acid. Assess each statement one by one to identify which is false.

Review Statement 1

Statement 1 says that boron is in sp3 hybridization in boric acid. Boric acid has the formula H3BO3, and in this molecule, boron is actually in sp2 hybridization, forming triangular planar BO3 units. Therefore, Statement 1 is false.

Review Statement 2

Statement 2 claims that boric acid has a layer structure where planar BO3 units are linked by hydrogen bonding. This is true because the structure of boric acid involves such layer formation.

Review Statement 3

Statement 3 suggests boric acid can be used as a solid lubricant. This is true because its layered structure allows for layers to slip over each other, providing lubricating properties.

Review Statement 4

Statement 4 claims that different layers in boric acid are held together by weak Van der Waals forces. This is also true as the layers interact through these weak forces.

Key concepts

sp2 hybridization

Boric acid (H3BO3) features boron in an sp2 hybridization state. This hybridization occurs when one s-orbital and two p-orbitals on the boron atom mix to form three equivalent hybrid orbitals.
This allows boron to form three sigma bonds, each with an oxygen atom. This configuration results in a trigonal planar shape for each BO3 unit.
The bond angles between the oxygen atoms are approximately 120 degrees, which is a typical feature of sp2 hybridization.
This arrangement provides the foundation for boric acid's unique structural properties.

Layer structure

Boric acid exhibits a distinct layer structure. In this configuration, individual BO3 units are coplanar, forming extensive two-dimensional sheets.
These layers stack on top of one another, creating a laminar material.
The planar BO3 units are bonded covalently, which results in strong intralayer bonds. However, the interaction between these layers is much weaker.
Understanding this layered arrangement is crucial in explaining many of boric acid's physical properties, such as its use in applications like solid lubricants.

Hydrogen bonding

In boric acid, hydrogen bonding plays a key role in maintaining its structural integrity. Within each layer, hydrogen bonds form between hydrogen atoms attached to oxygen and the adjacent oxygen atoms of neighboring BO3 units.
These hydrogen bonds are responsible for connecting the planar BO3 units and help maintain the stability of the layers.
Hydrogen bonding is a type of dipole-dipole interaction that is generally stronger than van der Waals forces but weaker than covalent bonds.
This type of bond not only stabilizes the layers but also plays a role in the solubility and melting point of boric acid.

Van der Waals forces

The layers in boric acid are held together by weak van der Waals forces. These forces are present between molecules or parts of molecules that arise from transient charge imbalances.
Despite being relatively weak compared to hydrogen bonds or covalent bonds, van der Waals forces are significant in materials like boric acid.
They enable the layers to slip over one another easily, which provides boric acid with its lubricating properties.
Understanding these forces helps explain why boric acid can act as a solid lubricant, as the layers can move with minimal resistance.