Question

Borax when dissolved in water exhibits (1) alkaline nature (2) acidic nature (3) neutral behaviour (4) amphoteric behaviour

Short answer

Alkaline nature

Step-by-step solution

Analyze Borax in Water

When borax (sodium tetraborate) dissolves in water, it undergoes hydrolysis. This means it reacts with water to form boric acid and sodium hydroxide (NaOH).

Chemical Equation

Write the hydrolysis reaction of borax in water: \[ Na_2B_4O_7 + 7H_2O \rightarrow 4H_3BO_3 + 2NaOH \] Sodium hydroxide (NaOH) is a strong base.

Determine the Nature

Since sodium hydroxide is a strong base, the solution becomes alkaline. This means borax in water exhibits an alkaline nature.

Key concepts

alkaline nature

When discussing the behavior of borax in water, it's important to understand its alkaline nature. Borax, also known as sodium tetraborate, changes the water's pH when it dissolves. This is because borax undergoes a specific chemical reaction called hydrolysis, leading to the formation of a strong base. An alkaline solution has a pH greater than 7. This is the opposite of an acidic solution, which has a pH less than 7. The presence of sodium hydroxide, a strong base, makes the solution of borax in water turn alkaline, which means the solution has a pH above 7. Therefore, borax in water will exhibit an alkaline nature.

hydrolysis reaction

Borax undergoes a key chemical process called hydrolysis when dissolved in water. Hydrolysis is a reaction involving the breaking of a bond in a molecule using water. Specifically, for borax:

• The hydrolysis reaction of borax can be represented as:
\[ Na_2B_4O_7 + 7H_2O \rightarrow 4H_3BO_3 + 2NaOH \]
• During this reaction, borax molecules split in the presence of water to form boric acid (\(H_3BO_3\)) and sodium hydroxide (\(NaOH\)).
• Boric acid is a weak acid, while sodium hydroxide is a strong base.
• Since sodium hydroxide is produced, the overall nature of the solution becomes alkaline—meaning it has a higher pH.

The hydrolysis of borax in water is fundamental to understanding why borax imparts an alkaline property to the solution.

sodium hydroxide

When borax dissolves in water, one of the products formed is sodium hydroxide (\(NaOH\)). Sodium hydroxide is a strong base, and its presence is key to the alkaline nature of the borax solution. To understand how \(NaOH\) influences the solution:

• \(NaOH\) dissociates completely in water, releasing hydroxide ions (\(OH^-\)).
• The formula for this dissociation is: \[ NaOH \rightarrow Na^+ + OH^- \]
• The hydroxide ions increase the basicity of the solution, raising the pH to greater than 7.
• This creates an alkaline environment, which is crucial for many chemical processes and reactions.

The production of sodium hydroxide during the hydrolysis of borax highlights why borax solutions are alkaline by nature.