---
title: "Calcination and slaking of lime"
subject: "Civil Engineering Materials"
chapter: 4
key: "semester_3/civil_engineering_materials:calcination-slaking-lime"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/calcination-slaking-lime
site: BCT Engineering
---

# Calcination and slaking of lime

Civil Engineering Materials · Chapter 4: Lime

- Asked in: 2081 Baisakh, 2 marks; 2073 Shrawan, 2 marks; 2071 Chaitra, 1 marks (asked 3 times)
- Video: [Limestone Cycle - limestone, quicklime and slaked lime | Chemistry | FuseSchool](https://www.youtube.com/watch?v=9LDG9cnGlDo) — FuseSchool - Global Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/calcination-slaking-lime
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-4

## Question

What do you mean by calcination and slaking (hydration) of lime?

## Short answer

Calcination is the burning of limestone at 900–1000°C to drive off CO₂ and produce quicklime (CaO). Slaking is the addition of water to quicklime, causing a vigorous reaction with heat and expansion, forming slaked lime (Ca(OH)₂).

## Answer

#### Calcination
**Calcination** is the burning of limestone at 900 to 1000 °C in a kiln, which drives off carbon dioxide and gives quicklime.

$$
\text{CaCO}_3 \xrightarrow{\ 900^\circ\text{C}\ } \text{CaO} + \text{CO}_2
$$

#### Slaking (hydration)
**Slaking** is the addition of water to quicklime. It reacts violently, gives out heat, swells to 2 to 2.5 times its volume and turns into slaked lime (calcium hydroxide) in powder or paste form.

$$
\text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{heat}
$$

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Calcination of limestone is done at:
   A. 100 degrees C
   B. 300 degrees C
   C. 1500 degrees C
   D. 900 to 1000 degrees C
   Answer: D. CaCO3 gives CaO and CO2. (Key point: Calcination)

2. Calcination drives off:
   A. Carbon dioxide
   B. Water
   C. Oxygen
   D. Nitrogen
   Answer: A. Quicklime is left. (Key point: Product)

3. Slaking is:
   A. Heating limestone
   B. Adding water to quicklime to form Ca(OH)2 with heat
   C. Adding CO2
   D. Adding clay
   Answer: B. It swells 2 to 2.5 times. (Key point: Slaking)

## Related in Civil Engineering Materials

- [Determining slaking nature of lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aslaking-nature-of-lime) — Civil Engineering Materials, chapter 4