Question

Name two metals which react violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved if any during the reaction?

Answer 1

Part:1

• Sodium and Potassium metals react violently with cold water.

Part 2: Observations

1. Metal will move over the surface of the water and give a hissing sound.
2. Metal starts reacting with water causing a little explosion
3. Quickly, the metal will catch the fire and then burn.

Part 3:

$\mathbf{2}\mathbf{K}\mathbf{}\mathbf{\left(}\mathbf{S}\mathbf{\right)}\mathbf{}\mathbf{+}\mathbf{}\mathbf{2}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{}\mathbf{\to }\mathbf{}\mathbf{2}\mathbf{KOH}\mathbf{}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{}\mathbf{+}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{}$

$\mathbf{2}\mathbf{Na}\mathbf{}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{}\mathbf{+}\mathbf{}\mathbf{2}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{}\mathbf{\to }\mathbf{}\mathbf{2}\mathbf{NaOH}\mathbf{}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{}\mathbf{+}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{}$

• The gas that evolved during the reaction can be identified bringing a burning candle near it.
• The candle will burn and give a pop sound on burning which implies the evolution of Hydrogen gas.