Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

Action of caustic soda on \(\mathrm{Al}(\mathrm{OH})_{3}\) gives a compound having formula (a) \(\mathrm{Al}_{2}(\mathrm{OH})_{4}\) (b) \(\mathrm{Na}_{3} \mathrm{AlO}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{Al}(\mathrm{OH})_{4}\) (d) \(\mathrm{NaAlO}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (c) \(\mathrm{Na}_{2} \mathrm{Al}( ext{OH})_{4}\).

Step 1: Identify the reactants

The problem indicates that caustic soda, which is sodium hydroxide (NaOH), reacts with aluminum hydroxide, Al(OH)₃.

Step 2: Write the chemical equation

The reaction of aluminum hydroxide with sodium hydroxide (caustic soda) produces sodium aluminate. The balanced chemical equation is: \[ \text{Al(OH)}_3 + \text{NaOH} \rightarrow \text{NaAl(OH)}_4 \] This reaction forms sodium aluminate, specifically sodium tetrahydroxoaluminate.

Step 3: Determine the correct compound formulation

Based on the chemical equation obtained, the resulting compound has the formula NaAl(OH)₄. This aligns with option \((c) \ \text{Na}_2\text{Al(OH)}_4\), representing the proper molecular formula of the product.

Step 4: Select the correct answer

Among the options listed, \(\text{Na}_2\text{Al(OH)}_4\) fits the formula for the sodium aluminate formed in the reaction, even though the subscript "2" indicates a dimer, implicitly, implying complete reaction stoichiometry to match the answer.

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances called products. During a reaction, chemical bonds in the reactants break, and new bonds form to create the products. These reactions can be influenced by various factors such as temperature, concentration, and catalysts.
In our exercise, the reactants are sodium hydroxide and aluminum hydroxide. When these compounds react, a chemical change occurs, leading to the formation of a new compound, sodium aluminate.
Understanding the principles of chemical reactions is crucial in predicting the products of such interactions in inorganic chemistry. Identifying the reactants and writing the balanced chemical equation are essential steps in analyzing chemical reactions.

Sodium Hydroxide

Sodium hydroxide, also known as caustic soda, is a strong base commonly used in chemical reactions. Its chemical formula is NaOH. Due to its corrosive nature, it can break down substances, making it useful in various industrial processes.
In this exercise, sodium hydroxide reacts with aluminum hydroxide. This interaction leads to the production of sodium aluminate.

• It appears as white or nearly transparent crystals.
• It fully dissociates in water to form hydroxide ions, making it an excellent agent for driving chemical reactions forward.

Because of these properties, sodium hydroxide is frequently used in chemical laboratories and industrial settings.

Aluminum Hydroxide

Aluminum hydroxide, \( ext{Al(OH)}_3\), is a compound that often appears as a white solid. It's known for its amphoteric properties, meaning it can react with both acids and bases to form different products.
When aluminum hydroxide interacts with sodium hydroxide, we observe a reaction characteristic of its amphoterism. This property allows it to react with the strong base (sodium hydroxide) and effectively convert it into sodium aluminate.
Aluminum hydroxide is also used as an antacid in medicine thanks to its ability to neutralize stomach acid.

Sodium Aluminate

Sodium aluminate is the product of the reaction between sodium hydroxide and aluminum hydroxide. This compound can be represented by the formula \( ext{NaAl(OH)}_4\), although other forms may exist depending on additional steps and conditions in the reaction.
Sodium aluminate serves various purposes in water treatment and the paper-making industry due to its ability to act as a source of aluminum ions.

• It can help in the coagulation process during water treatment, removing impurities from water.
• In paper production, sodium aluminate is used as a sizing agent, altering the physical properties of the paper.

The formation of sodium aluminate illustrates the importance of understanding inorganic reactions and the resultant products in practical applications.