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Reaction of water with metals

Answer Text:
Reactions of water with metals:
1. Potassium.
Procedure:
- A small piece of potassium metal is cut and dropped into a trough containing water;
- The resultant solution is tested with litmus paper;
Diagram of apparatus:

Observations and explanations:
- The metal floats on the water surface; because it is less dense than water;
-A hissing sound is produced; due to production of hydrogen gas;
- It explosively melts into a silvery ball then disappears because reaction between water and potassium is exothermic (produces heat).
The resultant heat melts the potassium due to its low melting point.
- It darts on the surface; due to propulsion by hydrogen;
- The metal bursts into a lilac flame; because hydrogen explodes into a flame which then burns the small quantities potassium vapour produced during the
reaction;
- The resultant solution turns litmus paper blue; because potassium hydroxide solution formed is a strong base;
(b). Reaction equations.
Equation I
#2K(s) + 2H_2O(l) → 2KOH(aq) + H_2(g)#;
Equation II
#4K(s) + O_2 (g) → 2K_2O(s)#;
Equation III:
#K_2O(s) + H_2O(l) → 2KOH(aq)#
Effect of resultant solution on litmus paper;
- Litmus paper turns blue; potassium hydroxide formed is highly soluble in water; releasing a large number of hydroxyl ions which result into alkaline conditions // high pH;