Which of the following is obtained upon heating ferrous sulphate?

Question

Examoogle · Accepted Answer

The correct answer is Option B: Ferric oxide, sulphur dioxide and sulphur trioxide. When green vitriol (ferrous sulphate heptahydrate) is heated, it first loses its water of crystallization to become anhydrous ferrous sulphate. On further strong heating, it decomposes to form ferric oxide along with sulphur dioxide and sulphur trioxide gases.

Step-by-Step Solution & Concepts:
When green vitriol (ferrous sulphate heptahydrate) is heated, it first loses its water of crystallization to become anhydrous ferrous sulphate. On further strong heating, it decomposes to form ferric oxide along with sulphur dioxide and sulphur trioxide gases.

Working Principle: The thermal decomposition of ferrous sulphate ($FeSO_4 \cdot 7H_2O$) takes place in two stages. First, heating removes water of crystallization to yield dirty white anhydrous $FeSO_4$. Upon stronger heating, anhydrous ferrous sulphate decomposes endothermically into reddish-brown ferric oxide ($Fe_2O_3$), sulphur dioxide ($SO_2$), and sulphur trioxide ($SO_3$) according to the chemical equation: $$2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)$$.

Key Formulas: $2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)$ — Thermal decomposition of ferrous sulphate

Key Points: Hydrated ferrous sulphate ($FeSO_4 \cdot 7H_2O$) is green in color.; On heating, it first loses 7 molecules of water of crystallization to form anhydrous white/grey powder.; On further heating, it decomposes into ferric oxide (red-brown residue), sulphur dioxide, and sulphur trioxide.; Characteristic choking smell of burning sulphur indicates the evolution of $SO_2$ and $SO_3$ gases.

Applications: Preparation of sulphur dioxide and sulphur trioxide in laboratories; Understanding the concept of thermal decomposition and water of crystallization

Additional Info: This reaction is a classic example of a thermal decomposition reaction taught in secondary school chemistry.. Option B is the correct choice since all three products ($Fe_2O_3$, $SO_2$, and $SO_3$) are formed.

Answer: B is correct — Ferric oxide, sulphur dioxide and sulphur trioxide are obtained upon heating ferrous sulphate.

Exam Tip: Always remember that salts containing water of crystallization undergo a two-step transformation upon heating: dehydration followed by chemical decomposition.

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