Classify Reactions: Combination MCQs Quiz | Class 10
This quiz covers important Multiple Choice Questions (MCQs) on ‘Classify Reactions: Combination’ from Class X Science (Code 086), Unit I: Practicals. Specifically, it focuses on the ‘Action of water on quicklime’. Test your knowledge and remember to submit your answers to see your score, then download a PDF of your results for review.
Understanding Combination Reactions: Quicklime and Water
Combination reactions are fundamental in chemistry, where two or more reactants combine to form a single, more complex product. This quiz specifically focused on a classic example: the reaction between quicklime and water.
Key Concepts Explained:
1. Combination Reaction: A chemical reaction in which two or more elements or compounds combine to form a single new compound. The general form is A + B → AB. For example, the formation of water from hydrogen and oxygen (2H2 + O2 → 2H2O).
2. Quicklime (Calcium Oxide, CaO): It is a white, caustic, alkaline, crystalline solid at room temperature. It is produced by the thermal decomposition of materials like limestone (calcium carbonate, CaCO3) in a lime kiln.
3. Action of Water on Quicklime: When water is added to quicklime, a vigorous chemical reaction occurs. The quicklime (calcium oxide) combines with water to form calcium hydroxide. This reaction releases a large amount of heat, making it a highly exothermic process.
The chemical equation for this reaction is: CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
4. Slaked Lime (Calcium Hydroxide, Ca(OH)2): The product formed from the reaction of quicklime with water is called slaked lime. It is sparingly soluble in water and is commonly used in various industrial processes, including building materials (mortar, plaster), water treatment, and agriculture to neutralize acidic soils.
5. Exothermic Reaction: This is a type of chemical reaction that releases energy by light or heat to its surroundings. The quicklime-water reaction is a prime example, causing the mixture to heat up significantly.
Quick Revision Points:
- Quicklime is Calcium Oxide (CaO).
- Water reacts vigorously with quicklime.
- The reaction is a combination reaction.
- The product is Slaked Lime (Calcium Hydroxide, Ca(OH)2).
- It is a highly exothermic reaction, meaning it releases heat.
- The general equation is Reactant A + Reactant B → Single Product.
Practice More:
- What happens chemically when slaked lime is exposed to air for a long time?
- Provide an example of a combination reaction involving two elements.
- How is quicklime obtained from limestone?
- What are two practical applications of slaked lime?
- Why is it important to handle quicklime with care, especially when adding water?
Content created and reviewed by the CBSE Quiz Editorial Team based on the latest NCERT textbooks and CBSE syllabus. Our goal is to help students practice concepts clearly, confidently, and exam-ready through well-structured MCQs and revision content.