Paper: CSIR-NET June 2016 · Subject: Inorganic Chemistry · Chapter: Analytical Chemistry · Topic: Analytical Chemistry – General · Marks: 2 · Difficulty: Medium
Decomposition temperature of $\mathrm{CaCO_3}$ in thermogravimetric analysis will be highest in dynamic atmosphere of:
(a)nitrogen
(b)synthesis gas
(c)1:1 mixture of $\mathrm{O_2}$ and CO
(d)water gas
Answer
Answer: C ✓ checked by 4AB · confidence medium
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
CaCO₃(s) ⇌ CaO(s) + CO₂(g). The higher the partial pressure of CO₂ in the purge gas, the further this equilibrium is pushed back (Le Chatelier), so the decomposition temperature seen in TGA rises. Nitrogen, synthesis gas and water gas (CO + H₂) supply little or no CO₂. In a 1:1 O₂ + CO stream, CO burns to CO₂ (2CO + O₂ → 2CO₂), so the sample sits in a CO₂-rich atmosphere and decomposes at the highest temperature. Answer: (c).