Group 1 metal reactions with water

From igcse chemistry edexcel specification.

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Lithium's reaction with water

When added to water:

  • Lithium floats on the surface, 
  • Gently fizzes and gives off hydrogen
  • It gradually reacts and disappears 
  • Forms a colourless solution of lithium hydroxide. 
  • The reaction generates heat too slowly and lithium's melting point is too high for it to melt.

Equation for reaction:

lithium + water ==> lithium hydroxide + hydrogen

2Li(s) + 2H20(l) --->  2LiOH(aq) + H2(aq)  

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Sodium's Reaction with water

When added to water: 

  • Sodium also floats on the surface 
  • Enough heat is given off to melt the sodium (sodium has a lower melting point than lithium and the reaction produces heat faster
  • It melts almost at once to form a small silvery ball that dashes around the surface. 
  • A white trail of sodium hydroxide is seen in the water under the sodium
  • This soon dissolves to give a colourless solution of sodium hydroxide.

Note: The sodium moves because it is pushed around by the hydrogen which is given off during the reaction. If the sodium becomes trapped on the side of the container, the hydrogen may catch fire to burn with an orange flame. The colour is due to contamination of the normally blue hydrogen flame with sodium compounds.

Equarion for Reaction:

sodium + water ----> sodium hydroxide + hydrogen

2Na(s) + 2H20(l) --->  2NaOH(aq) + H2(aq)

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Potassium's reaction with water

When added to water:

  • Potassium behaves rather like sodium except that the reaction is faster 
  • Enough heat is given off to ignite the hydrogen. 
  • This time the normal hydrogen flame is contaminated by potassium compounds and so is coloured lilac.
  • The reaction often ends with potassium spitting around

Equation for the reaction:

potassium + water ---> potassium hydroxide + hydrogen 

2K(s) + 2H20(l) --->  2KOH(aq) + H2(aq)

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Rubidium's reaction with water

When added to water:

  • Rubidium is denser than water and so sinks
  • It reacts violently and immediately
  • Reaction can be explosive
  • Everything spits out of the container. 
  • Rubidium hydroxide solution and hydrogen are formed.

Equation for reaction:

Rubidium + water ----> Rubidium hydroxide + hydrogen

2Rb(s) + 2H20(l) --->  2RbOH(aq) + H2(aq)  

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Caesium's reaction with water

When added to water:

  • Caesium explodes on contact with water, 
  • Quite possibly shattering the container. 
  • Explosive and violent reaction
  • Caesium hydroxide and hydrogen are formed.

Equation for reaction:

caesium + water ==> caesium hydroxide + hydrogen

2Cs(s) + 2H2O(l) ==> 2CsOH(aq) + H2(g)

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