In this post, you will get the Cement chapter questions and answers (short questions and answers) of the Applied Chemistry or Engineering Chemistry Book of Diploma or Polytechnic Engineering Students and B.Tech. Engineering 1st Year Students. In the post we have many short questions and their answers of cement chapter. Students have to go through this to score better in final exam because these questions are very important.
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Cement Chapter Questions and Answers | Applied Chemistry for Engineering 1st Year Students
Here we have listed some questions and answers of cement chapter of applied chemistry or engineering chemistry book –
1. How is gypsum converted to Plaster of Paris?
When gypsum (CaSO₄·2H₂O) is heated at about 100–120°C, it loses three-fourths of its water of crystallisation and forms Plaster of Paris (CaSO₄·½H₂O).
Equation:
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
2. What is Portland Cement?
Portland cement is a fine gray powder obtained by grinding clinker formed by heating a mixture of calcareous and argillaceous materials to a high temperature. It hardens when mixed with water due to hydration.
3. What are cement mortar and cement concrete? Mention their uses.
Cement mortar: A mixture of cement, sand, and water.
Cement concrete: A mixture of cement, sand, water, and coarse aggregate like gravel.
Uses:
- Cement mortar: Used in plastering and masonry work.
- Cement concrete: Used in construction of buildings, bridges, and roads.
4. Write down the reactions (with equations) that take place during setting and hardening of cement.
During setting:
Tricalcium aluminate and tricalcium silicate react with water to form a gel.
2(3CaO·SiO₂) + 6H₂O → 3CaO·2SiO₂·3H₂O + 3Ca(OH)₂
During hardening:
The gel of calcium silicate hydrate hardens and gives strength to cement.
5. What is meant by lime mortar and cement mortar?
Lime mortar: A mixture of lime, sand, and water used for plastering and masonry.
Cement mortar: A mixture of cement, sand, and water providing stronger and faster setting.
6. What are the disadvantages of using excess lime during manufacture of cement?
If excess lime is added during cement manufacture, the cement becomes unsound and may disintegrate. It produces less strength because free lime reacts slowly with water and leads to cracking.
7. Write down the formula of Plaster of Paris.
Formula: CaSO₄·½H₂O
8. Write down the starting material used for the manufacture of Portland cement.
Starting materials:
- Calcareous materials (like limestone)
- Argillaceous materials (like clay or shale)
9. Describe the process of manufacture of Portland cement either by dry process or wet process.
Steps involved:
- Crushing and grinding: Raw materials are crushed and ground.
- Mixing: Proper proportions of lime and clay are mixed.
- Heating: The mixture is heated in a rotary kiln at 1400–1500°C to form clinker.
- Grinding: The cooled clinker is mixed with 2–3% gypsum and ground to a fine powder to obtain cement.
10. State sequentially the chemical reactions that occur during setting and hardening of cement (write with equations).
Setting reactions:
2(3CaO·SiO₂) + 6H₂O → 3CaO·2SiO₂·3H₂O + 3Ca(OH)₂
Hardening reactions:
3CaO·Al₂O₃ + 6H₂O → 3CaO·Al₂O₃·6H₂O
These hydration products crystallize and interlock, giving strength to the cement paste.