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REACTION OF METALS WITH WATER

REACTION OF METALS WITH WATER

The higher the metal in the reactivity series the more reactive the metal with water. The following experiments show the reaction of metals with cold water and water vapour/steam.

 

(a) Reaction of sodium/ potassium with cold water:

Procedure

Put about 500cm3 of water in a beaker. Add three drops of phenolphthalein indicator/litmus solution/universal indicator solution/methyl orange indicator into the water.

Cut a very small piece of sodium .Using a pair of forceps put the metal into the water.

 

Observation

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

Colour of litmus solution turns blue

Colour of methy orange solution turns Orange

Colour of universal indicator solution turns blue

 

Explanation

Sodium is less dense than water. Sodium floats on water and vigorously reacts to form an alkaline solution of sodium hydroxide and producing hydrogen gas. Sodium is thus stored in paraffin to prevent contact with water.

 

Chemical equation

Sodium + Water -> Sodium hydroxide + Hydrogen gas

2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)

To collect hydrogen gas , Sodium metal is forced to sink to the bottom of the trough/beaker by wrapping it in wire gauze/mesh. Burning a candle 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

 

Chemical equation

Potassium + Water -> Potassium hydroxide + Hydrogen gas

2K(s) + 2H2O(l) -> 2KOH(aq) + H2(g)

Caution: Reaction of Potassium with water is very risky to try in a school laboratory.

 

(b) Reaction of Lithium/ Calcium with cold water:

Procedure

Put about 200cm3 of water in a beaker. Add three drops of phenolphthalein indicator/litmus solution/universal indicator solution/methyl orange indicator into the water.

Cut a small piece of Lithium.

Using a pair of forceps put the metal into the water. Repeat with a piece Calcium metal

 

Observation

Lithium sinks to the bottom of the water. Rapid effervescence/fizzing/ bubbles of colourless gas produced.

Colour of phenolphthalein turns pink

Colour of litmus solution turns blue

Colour of methy orange solution turns Orange

Colour of universal indicator solution turns blue

 

Explanation

Lithium and calcium are denser than water. Both sink in water and vigorously react to form an alkaline solution of Lithium hydroxide / calcium hydroxide and producing hydrogen gas.

Lithium is more reactive than calcium.

It is also stored in paraffin like Sodium to prevent contact with water.

 

Chemical equation

Lithium + Water -> Lithium hydroxide + Hydrogen gas

2Li(s) + 2H2O(l) -> 2LiOH(aq) + H22(g) Calcium + Water -> Calcium hydroxide + Hydrogen gas Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)

(c) Reaction of Magnesium/Zinc/ Iron with Steam/water vapour:

Procedure method 1

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:

(i) Drive away air in the ignition/hard glass boiling tube.

(ii) Generate steam

Heat the coiled ribbon strongly using another burner. Repeat the experiment using Zinc powder and fresh Iron filings.

Set up of apparatus

 

Observations

(i) With Magnesium ribbon:

The Magnesium glow with a bright flame (and continues to burn even if heating is stopped) White solid /ash formed

White solid /ash formed dissolve in water to form a colourless solution

Colourless gas produced/collected that extinguish burning splint with “pop sound”

 

(ii) 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.

(iii) With Iron fillings:

The Iron fillings turn red hot on strong heating

Dark blue solid formed

Dark blue solid formed does not dissolve in water.

 

Procedure method 2

Put some water in a round bottomed flask

Polish magnesium ribbon using sand paper.

Coil it at the centre of a hard glass tube

Set up the apparatus as below.

Heat water strongly to boil so as to:

(i) Drive away air in the glass tube.

(ii) Generate steam

Heat the coiled ribbon strongly using another burner. Repeat the experiment using Zinc powder and fresh Iron filings.

 

Method 2: Reaction of Steam with Magnesium Zinc/iron

Observations

(i) With Magnesium ribbon:

The Magnesium glow with a bright flame (and continues to burn even if heating is stopped) White solid /ash formed

White solid /ash formed dissolve in water to form a colourless solution

Colourless gas produced/collected that extinguish burning splint with “pop sound”

 

(ii) 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.

 

(iii)With Iron fillings:

The Iron fillings turn red hot on strong heating

Dark blue solid formed

Dark blue solid formed does not dissolve in water.

 

Explanations

(a) 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 .It extinguishes a burning splint with a “pop sound”.

 

Chemical Equation

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

 

Chemical Equation

Magnesium oxide + Water ->Magnesium hydroxide MgO(s) + H2O(l) -> Mg(OH) 2 (aq) (b)Hot Zinc react vigorously in steam forming yellow Zinc oxide solid/ash as residue which cools to white.

Hydrogen gas is produced .It extinguishes a burning splint with a “pop sound”.

 

Chemical Equation

Zinc + Steam -> Zinc oxide + Hydrogen Zn(s) + H2O(g) ->ZnO(s) + H2(g)

(b) Zinc oxide does not dissolve in water.

(c) Hot Iron reacts with steam forming dark blue tri iron tetra oxide solid/ash as residue.

Hydrogen gas is produced .It extinguishes a burning splint with a “pop sound”.

Chemical Equation Iron + Steam -> Tri iron tetra oxide + Hydrogen 2Fe(s) + 4H2O(g) -> Fe2O4(s) + 4H2(g) Tri iron tetra oxide does not dissolve in water.

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

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

 

See also:

WATER POLLUTION

WATER

REACTIVITY SERIES OF METALS/ELEMENTS

REACTION OF NON-METALS WITH OXYGEN/AIR

REACTION OF METALS WITH OXYGEN/AIR

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