question_answer 73)

    When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (molecular mass =40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.

Answer:

                    Molecular formula of Y = XOH Let the atomic weight of metal X is a. Then, molecular mass of XOH = a + 16 + 1 = 40 (Given) a = 40 ? 17 = 23 Thus, metal X is sodium (Na) because 23 is the atomic weight of sodium metal. Sodium reacts with water as Sodium (Na) gives hydrogen gas (Z) on reaction with cold water. So, Y is(sodium hydroxide). Z is H2 (hydrogen gas).