Problem 24 - A Complete Resource Book in Chemistry for JEE Main

Question

One can obtain a silica garden if (a) silicon salts are grown in garden (b) crystals of coloured cations are added to a strong solution of sodium silicate (c) silicon tetrafluoride is hydrolyzed (d) sodium silicate solution is heated with a base

Step-by-Step Solution

Answer

(b) Crystals of coloured cations are added to a strong solution of sodium silicate.

Step 1: Understanding the Question

The question asks which of the given options results in the creation of a silica garden. A silica garden is typically formed through a chemical reaction involving sodium silicate and coloured salts.

Step 2: Evaluating Option (a)

Option (a) suggests growing silicon salts in a garden, which does not relate to the typical chemical process needed to produce a silica garden. This option is incorrect because a physical setup of growing salts does not result in the necessary reaction.

Step 3: Evaluating Option (b)

Option (b) involves adding crystals of coloured cations to a strong solution of sodium silicate. This aligns with the typical method for creating a silica garden, where the cations react with the silicate to form structures. This is the correct option.

Step 4: Evaluating Option (c)

Option (c) involves hydrolyzing silicon tetrafluoride, which does not produce a silica garden. Instead, hydrolysis of silicon tetrafluoride results in silica and hydrogen fluoride, so this is incorrect.

Step 5: Evaluating Option (d)

Option (d) suggests heating sodium silicate solution with a base, which does not lead to the formation of a silica garden. Silica gardens are created with specific reactive salts, making this option incorrect.

Key Concepts

Sodium Silicate

Sodium silicate, often called "water glass," is a versatile chemical compound that plays a crucial role in forming silica gardens. It is a soluble compound in water and is composed of sodium oxide (Na2O) and silica (SiO2).

Sodium silicate solutions are used due to their ability to form gels when they react with certain ions or salts. When mixed with solutions containing metal cations, especially in a concentrated form, they produce fascinating structures like those in a silica garden.

These structures are not only visually appealing but also serve as a great example of inorganic chemical processes. The silicate anions in the solution react with coloured metal cations to create solid gel-like structures that rise from the solution and mimic plant growth.

• Soluble in water
• Reacts with metal cations
• Forms gels and solid structures

Chemical Reaction

At the heart of a silica garden is a chemical reaction between sodium silicate and certain metal salts containing coloured cations. When these two substances come in contact, they undergo a reaction that forms a solid silica gel structure.

The coloured cations diffuse slowly into the sodium silicate solution, where they exchange and react with the silicate ions. This leads to the formation of insoluble silicates which precipitate out as solid substances.

Over time, these reactions contribute to the growth of new, often brightly colored structures. This process continues until the available reactants are exhausted or the environmental conditions change.

• Involves sodium silicate and metal salts
• Produces insoluble silicates
• Continues with reactant availability

Coloured Cations

Coloured cations are essential for creating the vibrant and picturesque structures observed in silica gardens. These are typically metal ions such as copper, cobalt, iron, or manganese, which introduce distinct colors through their specific chemical properties.

As these cations interact with sodium silicate, they not only form solid structures but also color these formations. The result is an array of colors, with each metal ion contributing different hues.

This color-producing effect is due to transition metal ions' unique electronic configurations, allowing them to absorb and emit various wavelengths of light.

• Cobalt cations can produce blue hues
• Iron cations lead to yellow or brown shades
• Copper cations often create blue-green colors

These aesthetically pleasing reactions provide a platform for understanding more complex chemical interactions and principles.