Ferrous sulphate decomposes to which of the following substances? | General Science MCQ | Examoogle

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Ferrous sulphate decomposes to which of the following substances?

Ferric oxide ( $Fe_{2}O_{3}$ ), sulphur dioxide ( $SO_{2}$ ) and sulphur trioxide ( $SO_{3}$ )

Ferric oxide ( $Fe_{2}O_{3}$ ) and sulphur dioxide ( $SO_{2}$ ) only

Ferric oxide ( $Fe_{2}O_{3}$ ) only

Ferric oxide ( $Fe_{2}O_{3}$ ) and sulphur trioxide ( $SO_{3}$ ) only

Correct Answer

🔬 SC • Science Chemical Reaction PrincipleGeneral SciencePrevious Year Paper 2024

Option A

Ferric oxide ( $Fe_{2}O_{3}$ ), sulphur dioxide ( $SO_{2}$ ) and sulphur trioxide ( $SO_{3}$ )

Quick Summary:

When solid ferrous sulphate crystals are heated, they undergo thermal decomposition to form ferric oxide (a reddish-brown solid), sulphur dioxide (a pungent gas), and sulphur trioxide (a toxic gas). This reaction is a classic example of a thermal decomposition reaction used to demonstrate the effect of heat on metal salts.

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🔬SCScience SolutionChemical Reaction Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of it like heating a complex structure made of blocks that breaks down into smaller, simpler parts when it gets too 'hot' to maintain its original form.

🧠 Memory Mnemonic / Shortcut Aid

F-S-S-S: Ferrous Sulphate yields Solid-oxide, Sulphur-dioxide, and Sulphur-trioxide.

🔢 Key Formulas

$2FeSO_4(s) \rightarrow Fe_2O_3(s) + SO_2(g) + SO_3(g)$ — The thermal decomposition reaction of ferrous sulphate

⚙️ Working Principle

The reaction involves the heating of hydrated ferrous sulphate ( $FeSO_4 \cdot 7H_2O$ ). First, the water of crystallization is lost, turning the green crystals into anhydrous ferrous sulphate. Upon further heating, the anhydrous salt decomposes into solid ferric oxide ( $Fe_2O_3$ ), sulphur dioxide ( $SO_2$ ), and sulphur trioxide ( $SO_3$ ). The balanced chemical equation is: $2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)$ .

📌 Key Points

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Ferrous sulphate crystals are light green in color.
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The reaction is a thermal decomposition process.
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The gases $SO_2$ and $SO_3$ have a characteristic burning sulphur smell.
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The residue $Fe_2O_3$ is a reddish-brown solid.

✅ Advantages

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Used in laboratory to produce and identify acidic gases like sulphur oxides.

❌ Disadvantages / Limitations

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Produces toxic, choking gases ( $SO_2$ and $SO_3$ ); must be performed in a well-ventilated area or fume hood.

🛠️ Applications / Uses

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Used in the study of chemical kinetics and decomposition reactions.
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Preparation of iron(III) oxide.

📄 Additional Information

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The color change from light green to reddish-brown is a key visual indicator in this experiment.
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Option B, C, and D are incorrect as they omit one or more of the gaseous products liberated during the decomposition.

📊 Diagram / Illustration

✅

A is correct — Ferrous sulphate decomposes into ferric oxide, sulphur dioxide, and sulphur trioxide upon heating.

Core Concepts Used

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Thermal decomposition Chemical reaction balancing Oxidation-reduction

💡 EXAM TIP

Always remember that metal sulphates, when heated strongly, typically yield their respective metal oxides and acidic sulphur gases ( $SO_2, SO_3$ ).

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