CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 16(b)
Compare in tabular form the reactivities of the following metals with cold and hot water :
- (a)Sodium
- (b)Calcium
- (c)Magnesium
Answer
Sodium reacts violently with cold water, calcium less violently, magnesium only with hot water; reactivity falls from sodium to magnesium.
Sodium. Cold water: reacts violently; so much heat is evolved that the hydrogen formed catches fire. Hot water: reacts even more violently, and more heat is evolved.
Calcium. Cold water: reacts less violently than sodium; the heat evolved is not enough for the hydrogen to catch fire, and bubbles of hydrogen stick to the metal so that it floats. Hot water: reacts vigorously; bubbles of hydrogen stick to the metal and it floats on the water.
Magnesium. Cold water: does not react. Hot water: reacts to form magnesium hydroxide and hydrogen; bubbles of hydrogen stick to its surface and it floats on the water.
Reactivity with water: sodium > calcium > magnesium.
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