Which metal reacts violently with cold water, producing a metal hydroxide, hydrogen gas, and enough heat for the hydrogen to catch fire?
Potassium
Reactivity with water follows the reactivity series: the most reactive metals (like potassium and sodium) react even with cold water, while less reactive ones react only with steam or not at all.
Potassium reacts violently with cold water: \(2K + 2H_2O \rightarrow 2KOH + H_2\), giving potassium hydroxide and hydrogen. The reaction is so exothermic that the heat ignites the evolved hydrogen, producing a lilac flame.
Calcium reacts far more gently with cold water and does not catch fire; magnesium reacts only slowly with hot water/steam; aluminium is protected by an oxide layer and does not react with cold water.
Hence, the metal is potassium.
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Important Questions from Chemical Reaction
Which of the following statement is/are true?
I. In physical change new substance is formed. substance is formed.
II. In chemical change no new substance is formed.
Which of the following cells involves similar chemical reactions?
The information not obtained from balanced chemical equation is
Oxygen cannot be obtained by which one of the following methods?
Which of the following statement is correct?
I. Insoluble salt is obtained by precipitation reaction.
II. Addition of oxygen or loss of hydrogen is called oxidation.
