A student prepared 20% sodium hydroxide solution in a beaker containing water. The observations noted by him are given below. I. Sodium hydroxide is in the form of pellets. II. It dissolves in water readily. III. The beaker appears cold when touched from outside. IV. The red litmus paper turns blue when dipped into the solution. The correct observation are:
A student prepared 20% sodium hydroxide solution in a beaker containing water. The observations noted by him are given below. I. Sodium hydroxide is in the form of pellets. II. It dissolves in water readily. III. The beaker appears cold when touched from outside. IV. The red litmus paper turns blue when dipped into the solution. The correct observation are:
Options
The correct observations are I, II, and IV. Therefore, the correct option is D.
Marking Scheme
- 11 mark for selecting the correct option D and providing the correct justification regarding the exothermic nature of the dissolution of .
Hint
Recall that dissolving sodium hydroxide in water is a highly exothermic process, which releases heat. Also, consider the effect of a base on red litmus paper.
Quick Oral Answer
Sodium hydroxide is a strong base that exists as waxy white pellets. When dissolved in water, it readily dissolves in a highly exothermic process, making the beaker hot. Being basic, its solution turns red litmus paper blue.
Analysis & Explanation
Let us evaluate each observation based on the NCERT text:
- Statement I: Sodium hydroxide is indeed stored and used in the form of pellets, as mentioned in Activity 2.10 ('sodium hydroxide pellets'). This statement is correct.
- Statement II: Sodium hydroxide is an alkali (a base that dissolves in water) and dissolves readily in water. This statement is correct.
- Statement III: The text states in Activity 2.10 that 'The process of dissolving an acid or a base in water is a highly exothermic one.' Since the dissolution of in water is highly exothermic, heat is released, and the beaker will feel hot to the touch, not cold. Thus, this statement is incorrect.
- Statement IV: Since is a base, it turns red litmus paper blue. This statement is correct.
Since statements I, II, and IV are correct, the correct option is D.
Common Mistakes
- 1Students often confuse exothermic and endothermic processes, incorrectly assuming that the beaker becomes cold during dissolution.
- 2Misidentifying the acid-base nature of sodium hydroxide and its effect on litmus paper.
Interesting Facts
Sodium hydroxide is commonly known as caustic soda. The dissolution process is so exothermic that adding water directly to a large amount of pellets can cause the solution to splutter violently due to local boiling.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2013?
This question carries 1 mark in the CBSE Class 10 Science 2013 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Properties of Bases and Dissolution" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2013 paper?
This is a MCQ question from Section B in the CBSE Class 10 Science 2013 paper.