20g of limestone (solid) is solid heated strongly in an open vessel to leave a residue of quick lime weighing only 11.2 g . How can you justify this decrease of mass?
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Given:
The mass of limestone = 20 gm
The mass of residue left = 11.2 gm
To Find:
To justify the reason behind the decrease in mass.
Calculation:
- The thermal decomposition of Limestone is given as:
CaCO3 + Heat → CaO + CO2
- According to this reaction:
The mass of CO2 evolved on heating 100 gm CaCO3 = 44 gm
⇒ The mass of CO2 evolved on heating 20 gm CaCO3 = (44/100) × 20
⇒ m = 8.8 gm
- The mass of residue left = 10 - 8.8 = 11.2 gm
- As the mass of residue is the same, it verifies the law of conservation of mass.
- Hence, the decrease in mass is justified as it is due to the evolution of CO2 and it follows the law of conservation of mass.
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