Question

The metal M reacts vigorously with water to form a solution S and a gas G. The solution S turns red litmus to blue whereas gas G, which is lighter than air, burns with a pop sound. Metal M has a low melting point and it is used as a coolant in nuclear reactors.
(a) What is metal M?
(b) What is solution S? Is it acidic or alkaline?
(c) What is gas G?
(d) Write a balanced chemical equation for the reaction which takes place when metal M reacts with water.
(e) Is this reaction exothermic or endothermic?

Answer 1

Answer:

(a) Sodium, Na.

(b) Sodium hydroxide solution (NaOH solution), Alkaline.

(c) Hydrogen, H2

(d) 2Na + 2H2O —–> 2NaOH + H2

(e) Exothermic

Answer 2

(a) The metal M is sodium.

(b) The solution S is sodium hydroxide. It is an alkaline solution.  

(c) The gas G is hydrogen.

(d) The balanced chemical reaction between metal M and water is:

$2 N a+2 H_{2} O \rightarrow 2 N a O H+H_{2}$

(e) This reaction is an exothermic reaction.

Explanation:

• Sodium is a soft metal in silvery white colour. This is an alkali metal. The solution formed by sodium is a basic (alkaline) solution.
• The litmus paper is used to determine whether the solution is acidic and alkaline solution.
• The hydrogen gas does not react with air, as the result is produces red flame before putting out with water as product. The reaction between hydrogen and air is:  $2 H_{2(g)}+O_{2(g)} \rightarrow 2 H_{2} O_{(l)}$

• The sodium hydroxide or caustic soda is white salt which is basic in nature.  
• This reaction is an exothermic reaction as it produces heat energy.