Water and Hydrogen-Reactions of water with Metals

Introduction to Reactions of Water and Metals

Some metals react with water while others do not.
The reaction of metals with water depends on the reactivity series.
The higher the metal in the reactivity series the more reactive the metal with water

Reaction of Sodium/Potassium with Cold Water

An experiment is conducted as follows;
– Put about 500cm³ of water in a beaker
– Add three drops of phenolphthalein indicator into the water
– Cut a very small piece of sodium and put the metal into the water using a pair of forceps

NOTES
– Sodium melts to a silvery ball that floats and darts on the surface decreasing in size
– Effervescence/fizzing/ bubbles of colourless gas produced
– Colour of phenolphthalein turns pink
– Sodium is less dense than water, hence floats on water
– Sodium vigorously reacts with water to form an alkaline solution of sodium hydroxide and producing hydrogen gas
– Sodium is stored in paraffin to prevent contact with water

Sodium + Water  Sodium hydroxide + Hydrogen gas
2Na(s) + 2H₂O (l)  2NaOH (aq) + H₂ (g)

– Potassium is more reactive than Sodium
– On contact with water it explodes/burst into flames
– An alkaline solution of potassium hydroxide is formed and hydrogen gas

Potassium + Water  Potassium hydroxide + Hydrogen gas
2K(s) + 2H₂O (l)  2KOH (aq) + H₂ (g)

Reaction of Lithium/Calcium with Cold Water

An experiment is conducted as follows;
– Put about 200cm³ of water in a beaker
– Add three drops of phenolphthalein indicator into the water
– Cut a small piece of Lithium and put the metal into the water using forceps
– Repeat with a piece Calcium metal
NOTES
– Lithium sinks to the bottom of the water and rapid effervescence/fizzing/ bubbles of colourless gas produced
– Colour of phenolphthalein turns pink
– Lithium and calcium are denser than water.
– Both sink in water and vigorously react to form an alkaline solution and produce hydrogen gas.
– Lithium is more reactive than calcium and is also paraffin like Sodium to prevent contact with water
– The following equations are representative of the reactions that occur

Lithium + Water  Lithium hydroxide + Hydrogen gas
2Li(s) + 2H₂O (l)  2LiOH (aq) + H₂(g)

Calcium + Water  Calcium hydroxide + Hydrogen gas
Ca(s) + 2H₂O (l)  Ca (OH)₂(aq) + H₂(g)

Reaction of Magnesium/Zinc/Iron with Steam/water vapour

An experiment is conducted as follows;
– Place some wet sand or cotton/glass wool soaked in water at the bottom of an ignition/hard glass boiling tube
– Polish magnesium ribbon using sand paper
– Coil it at the centre of the ignition/hard glass boiling tube.
– Set up the apparatus as below

– Heat the wet sand or cotton/glass wool soaked in water gently to drive away air in the ignition/hard glass boiling tube and generate steam.
– Heat the coiled ribbon strongly using another burner
– Repeat the experiment using Zinc powder and fresh Iron filings

A. Reaction with Magnesium

The Magnesium glows with a bright flame. It continues to burn even if heating is stopped. White solid /ash that dissolve in water to form a colourless solution is formed. Colourless gas produced/collected that extinguish burning splint with “pop sound”

– Hot magnesium burn vigorously in steam
– The reaction is highly exothermic generating enough heat/energy to proceed without further heating
– White Magnesium oxide solid/ash is left as residue
– Hydrogen gas is produced and extinguishes a burning splint with a pop sound
Magnesium + Steam  Magnesium oxide + Hydrogen
Mg(s) + H₂O(g)  MgO(s) + H₂(g)

– Magnesium oxide reacts /dissolves in water to form an alkaline solution of Magnesium oxide
Magnesium oxide + Water  Magnesium hydroxide
MgO(s) + H₂O(l)  Mg(OH)₂(aq)

B. Reaction with Zinc Powder

The Zinc powder turns red hot on strong heating. Yellow solid formed that turn white on cooling. White solid formed on cooling does not dissolve in water.

– Hot Zinc react vigorously in steam forming yellow Zinc oxide solid/ash as residue which cools to white
– Hydrogen gas is produced and extinguishes a burning splint with a pop sound
Zinc + Steam  Zinc oxide + Hydrogen
Zn(s) + H₂O(g)  ZnO(s) + H₂(g)
– Zinc oxide does not dissolve in water

C. Reaction with Iron Fillings

The Iron fillings turn red hot on strong heating. Dark blue solid formed. The dark blue solid formed does not dissolve in water.

– Hot Iron reacts with steam forming dark blue tri iron tetra oxide solid/ash as residue
– Hydrogen gas is produced and extinguishes a burning splint with a pop sound
Iron + Steam  Tri iron tetra oxide + Hydrogen
2Fe(s) + 4H₂O(g  Fe₂O₄(s) + 4H₂(g)

D. Reaction with Aluminium

Aluminium reacts with steam forming an insoluble coat/cover of impervious layer of aluminium oxide on the surface preventing further reaction.

Note

Lead, Copper, Mercury, Silver, Gold and Platinum do not react with either water or steam.