What is the chemical composition of washing soda? | General Science MCQ | Examoogle

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What is the chemical composition of washing soda?

$Al_{2}(CO_{3})_{3} \cdot 10H_{2}O$

$Na_{2}SO_{4} \cdot 10H_{2}O$

$Al_{2}(SO_{4})_{3} \cdot 10H_{2}O$

$Na_{2}CO_{3} \cdot 10H_{2}O$

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral SciencePrevious Year Paper 2024

Option D

$Na_{2}CO_{3} \cdot 10H_{2}O$

Quick Summary:

Washing soda is the common name for sodium carbonate decahydrate. Its chemical formula is $Na_{2}CO_{3} \cdot 10H_{2}O$ .

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🔬SCScience SolutionConcept & Principle

💡 Explanation

Washing soda is the common name for sodium carbonate decahydrate. Its chemical formula is $Na_{2}CO_{3} \cdot 10H_{2}O$ .

💡 Everyday Analogy (Real-World Intuition)

Think of it like a sponge that has soaked up water; the 10 molecules of water are 'trapped' inside the crystal structure, making it look like a dry powder even though it is chemically hydrated.

🧠 Memory Mnemonic / Shortcut Aid

Remember 'Washing Soda has 10 Waters'—Sod-a for $Na_{2}CO_{3}$ and Deca (10) for $10H_{2}O$ .

🔢 Key Formulas

$Na_{2}CO_{3} \cdot 10H_{2}O$ — Chemical formula of washing soda

$Na_{2}CO_{3} + 10H_{2}O \rightarrow Na_{2}CO_{3} \cdot 10H_{2}O$ — Hydration process

⚙️ Working Principle

It is produced industrially via the Solvay process, where sodium bicarbonate is heated to form anhydrous sodium carbonate (soda ash). This is then recrystallized from water to incorporate ten molecules of water of crystallization, resulting in the stable crystalline form known as washing soda.

📌 Key Points

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It is a basic salt used to soften hard water.
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It is also known as sodium carbonate decahydrate.
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It is used in glass, soap, and paper industries.

✅ Advantages

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Highly effective in removing temporary and permanent hardness from water
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Acts as an excellent cleaning agent for laundry

❌ Disadvantages / Limitations

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Can be irritating to sensitive skin if used in high concentrations
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Efflorescent in nature: it loses its water of crystallization when exposed to dry air.

🛠️ Applications / Uses

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Softening of hard water
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Manufacturing of soaps and detergents

📄 Additional Information

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Sodium carbonate is also called 'soda ash' when anhydrous (without water).
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Option A ( $Al_{2}(CO_{3})_{3} \cdot 10H_{2}O$ ) is incorrect as Aluminum carbonate is unstable in water.
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Option B ( $Na_{2}SO_{4} \cdot 10H_{2}O$ ) is Glauber's salt, not washing soda.
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Option C ( $Al_{2}(SO_{4})_{3} \cdot 10H_{2}O$ ) is related to alum chemistry, not washing soda.

✅

D is correct — Washing soda is chemically represented as $Na_{2}CO_{3} \cdot 10H_{2}O$ .

Core Concepts Used

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Water of crystallization Sodium carbonate Chemical nomenclature

💡 EXAM TIP

Always differentiate between 'Baking Soda' ( $NaHCO_{3}$ ) and 'Washing Soda' ( $Na_{2}CO_{3} \cdot 10H_{2}O$ ) for competitive exams, as they are frequently tested.

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