Problem 72 - A Complete Resource Book in Chemistry for JEE Main

Question

Aluminium vessles should not be washed with materials containing washing soda because (a) washing soda reacts with aluminum to form insoluble aluminium oxide (b) washing soda reacts with aluminium to form soluble aluminate. (c) washing soda is expensive (d) washing soda is easily decomposed

Step-by-Step Solution

Answer

(b) washing soda reacts with aluminium to form soluble aluminate.

Step 1: Identify the Chemical Components

First, identify the substances involved in the problem. Washing soda, known as sodium carbonate, is represented chemically as \( Na_2CO_3 \). Aluminium, a metal, is represented by the symbol \( Al \). The problem asks about the chemical reaction between these components.

Step 2: Analyze the Possible Reactions

Evaluate the potential chemical reactions between aluminium and washing soda. One possibility is the formation of aluminium oxide, but the solubility of this compound is key to understanding the reaction's nature.

Step 3: Evaluate Reaction Outcomes

Consider the implications of each option: (a) suggests an insoluble oxide is formed, this implies a protective layer would form hindering further reaction. (b) suggests formation of a soluble aluminate, meaning aluminium would continue to erode. Options (c) and (d) are unrelated to chemical reactions.

Step 4: Eliminate Irrelevant Options

Option (c) about the expense and option (d) about decomposition of washing soda do not align with chemical reasoning regarding aluminium vessels. Therefore, eliminate these.

Step 5: Determine Reaction Impact on Aluminium

Compare remaining options: (a) and (b). Option (b), stating washing soda reacts with aluminium to form soluble aluminate, suggests a reaction that continuously interacts and degrades the aluminum, which is a valid reason for avoiding this washing method.

Key Concepts

Washing Soda

Washing soda is a highly effective cleaning agent that is chemically known as sodium carbonate (\( Na_2CO_3 \)). It is commonly used for a variety of household cleaning tasks thanks to its ability to soften water, remove stains, and clean surfaces. However, when it interacts with certain metals like aluminium, caution is necessary. The chemical nature of washing soda makes it more reactive under specific conditions, especially against certain metals including aluminum.

• Washing soda is often used to clean laundry, floors, and even soaking some kitchen utensils.
• Its alkaline properties make it excellent for cutting through grease and enhancing cleaning processes.

Despite its versatile use, one important aspect to consider is its reactive nature with metals, which leads us to the important discussion of aluminium and its reactions.

Aluminium Oxide

Aluminium oxide is an inorganic compound with the chemical formula \( Al_2O_3 \). It is a significant substance because of its properties and uses, particularly in industrial and manufacturing processes. When aluminum undergoes oxidation, aluminium oxide forms as a surface layer. This layer is typically known for being insoluble and protective, thus resisting further corrosion. However, washing soda does not usually lead to the formation of an insoluble aluminium oxide.

• Aluminium oxide acts as a protective barrier, famously making aluminium vessels more durable by keeping the metal surface beneath from further reacting with environmental elements.
• This property is often exploited in the production and use of various aluminum materials to ensure longevity.

The idea of forming this oxide when washing soda is present is a misunderstanding, as the interaction primarily leads to a different compound formation.

Soluble Aluminate

In the reaction of washing soda with aluminum, a more pertinent outcome is the formation of a soluble aluminate. This reaction occurs when aluminum reacts with the sodium ions in washing soda, leading to products that include a soluble sodium aluminate.

• Soluble aluminates result when the reaction allows the alloying elements to dissolve, which can compromise the structure of the aluminum over time.
• This leads to the continued degradation and potential damage to the aluminum vessels, which weakens their structural integrity.

It's this aspect of promoting continuous erosion that substantiates why washing soda should not be used for cleaning aluminum vessels. The solubility of the aluminate formed ensures the reaction proceeds, risking complete erosion of the aluminum material over repeated exposure.