question_answer

  Name two metals which react violently with cold water. Write any observation you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reactions?       [CBSE (AI) 2008]

Answer:

                  Metals which react violently with cold water are potassium (K) and sodium (Na). 2K + 2H2O®2KOH + H2 + Heat energy 2Na + 2H2O ® 2NaOH + H2 + Heat energy The hydrogen gas produced during the reactions of these two metals with water immediately catches fire. Thus, these reactions are violent and exothermic. The gas evolved during these reactions burns with a popping sound which confirms that the gas is hydrogen (H2).