Question

17. (i) Name two metals which react violently with cold water.

(ii) Write any three observations you would make when such a metal is dropped into water

(iii) How would you identify the gas evolved, if any, during the reaction ?

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Answer 1

Answer:

a. Answer: Metals which react violently with cold water are potassium (K) and sodium (Na). The hydrogen gas produced during the reactions of these two metals with water immediately catches fire.

Explanation:

b.Answer: Metals which react violently with cold water are potassium (K) and sodium (Na). The hydrogen gas produced during the reactions of these two metals with water immediately catches fire. Thus, these reactions are violent and exothermic.

c.How would you identify the gas evolved, if any, during the reactions? Answer: Metals which react violently with cold water are potassium (K) and sodium (Na). The hydrogen gas produced during the reactions of these two metals with water immediately catches fire.

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Answer 2

Answer :

i. Sodium and potassium are two metals react violently with water. They even react with cold water so violently that, the evolved hydrogen immediately catches fire.

Reactions:-

$\bold{1.}\:\rm{2K(s)+2H_2O(l)\longrightarrow{}2KOH(aq)+H_2(g)+Heat\:energy}$

$\bold{1.}\:\rm{2Na(s)+2H_2O(l)\longrightarrow{}2NaOH(aq)+H_2(g)+Heat\:energy}$

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ii.

• (a) When such a metal, say sodium is dropped in water it floats on the surface of water. This happens due to low density of sodium.

• (b) When put in water, It melts to form a silvery ball and starts sizzling on the surface of water giving tiny bubbles of a colourless gas. This happens due to the violent & exothermic reaction of sodium and water.

• (c)The sodium ball gradually decreases in size and finally disappears. This happens due to the excessive heat produced in the reaction. The heat produced melts up the sodium ball until it disappears.

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iii. The colourless gas evolved in the reaction is hydrogen. When a burning wooden splint or candle is brought near the gas, it burns with a "pop" sound and a blue coloured flame.