The process of adding water to lime to convert it into a hydrated lime is termed as:
💧 Understanding the Lime Cycle
The lime cycle involves two key processes. First, calcination is the heating of limestone (CaCO₃) to produce quicklime (CaO). The second critical step is adding water to this quicklime. This is an exothermic reaction (it releases a lot of heat) that converts the unstable quicklime into a more stable powder called hydrated lime or slaked lime.
The chemical reaction is:
$$ \text{CaO} (\text{Quicklime}) + \text{H}_2\text{O} (\text{Water}) \rightarrow \text{Ca(OH)}_2 (\text{Hydrated Lime}) + \text{Heat} $$
🔬 Detailed Analysis of the Options
D. slaking
This is the correct answer. "Slaking" is the specific industrial and construction term for the process of adding water to quicklime. The process is often violent, with the lumps of lime cracking, swelling, and releasing steam as they turn into a fine powder. This is the most precise term for the overall process.
C. hydration
This is a chemically correct term, as the reaction is indeed a hydration reaction (a substance combines with water). However, in the context of construction and lime technology, "slaking" is the more specific and commonly used term that describes the entire phenomenon, including the physical changes like swelling and heat generation.
A. watering
This is incorrect. "Watering" is a general term and does not describe this specific, vigorous chemical reaction.
B. baking
This is incorrect. Baking involves heating, which is the opposite of what is being done here. The process of heating lime is calcination, not baking.
📊 Summary: Calcination vs. Slaking
| Process | Input | Action | Output |
|---|---|---|---|
| Calcination | Limestone (CaCO₃) | Heating | Quicklime (CaO) |
| Slaking | Quicklime (CaO) | Adding Water | Hydrated Lime (Ca(OH)â‚‚) |
💡 Study Tips
- Slaking = Adding Water: This is the key association. Slaking is the process of adding water to quicklime.
- Slaking vs. Hydration: While chemically it's a hydration reaction, the industry term is "slaking." For MCQs, always choose the most specific technical term.
- Remember the Heat: Slaking is a highly exothermic process. Visualizing the lumps of lime hissing, steaming, and breaking apart can help you remember the term "slaking."