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  • An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved

An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved.

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Let, the atomic weight of alkali metal A is x. When it reacts with water it forms a compound B having molecular mass 40.
Let, the reaction is
2A+2H_{2}O\rightarrow 2AOH+H_{2}
Molecular mass of B = x + 16 + 1 = 40
x = 40 - 17 = 23
Hence A is Sodium (Na)
The reaction involved is:
2Na+2H_{2}O\rightarrow 2NaOH+H_{2}
So, compound B is sodium hydroxide (NaOH)
Sodium hydroxide reacts with aluminium oxide (Al2O3) to give sodium aluminate (NaAIO2)
Thus, C is sodium aluminate NaAIO2
The reaction involved is: 
Al_{2}O_{3}+2NaOH\rightarrow 2NaAlO_{2}+H_{2}O

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