Chemistry chapter 3 : Reactivity series and electro chemistry

 Difference in Reactivity of Metals

1. Reaction of metals with hot Water.

2. Reactions of metals with Air.

3. Reaction of metals with Acids.

1 Reaction of Metal with water:

Experiment: 

 Take three beakers having the same quantity of Water. Take pieces of sodium, Magnesium and copper of the same size and drop each one to each beaker. (Same procedure is repeated in hot water).

Observation:

Conclusion:

* The rate of reaction of metals with water is not the same.

*Sodium reacts vigorously with cold and hot water.

*Metals React with water to form Hydrogen gas.

*2Na +2H2O >> 2NaOH+ H2

*Decreasing order of their reactivity is Na>Mg>Cu.

a. Which gas is produced when Magnesium reacts with hot water?

Ans. Hydrogen 

b. Write down its balanced chemical equation.

Ans.  Mg + 2 H2O >> Mg(OH)2 + H2

c. Which metal does not react with cold water as well as hot water?

Ans.  Cu

2 Reactions of Metals with Air

 Freshly cut surfaces of metals will have a shiny appearance. This property is known as metallic lusture

Experiment:

Procedure:

* Cut a piece of sodium using a knife. Observe the freshly cut portion After some time .

Observation:

 Shining sodium fades.

Conclusion:

Sodium fades because Conversion of Sodium into its compounds by reacting with oxygen 

,moisture and carbon dioxide in the atmosphere.

4Na+ O2 >> 2Na2O

Na2O+ H2O >> 2NaOH

2 NaOH+ CO2 >> Na2CO3 + H2O

i). A fresh Magnesium ribbon losing its luster when kept exposed in the air for some days. This is also due to its reaction with atmospheric air

2Mg +O2 >>  2MgO

ii). It can be seen that the lustre of Aluminium vessels diminishes as time passes by.

4Al+ 3O2 >>  2Al2O3

iii). In the case of copper vessels, it takes months for the loss of its luster by the formation of verdigris.

 

iv). Shining of Gold does not fade because it does not react with oxygen, moisture in the atmosphere.

v). Metals react with air at different rates.

vi). Above metals, Decreasing order of their reactivity with air and thereby losing luster is Sodium> Magnesium> Aluminium>Copper>Gold.

3 Reactions of Metals with Acids:

Experiment:

 Take 5 test tubes having the same quantity of dil:HCl . Take pieces of Fe, Mg, Cu, Pb & Zn 

of the same size and drop each one to each test tube

Observation.

Conclusion:

*Metals react with dil: HCl to form Hydrogen.

* The rate of reaction of metals with acid is not the same.

*Metals differ in their reactivity. Arrange above metals in the decreasing order is

Mg> Zn> Fe> Pb> Cu.

Reactivity Series:

* The series obtained by arranging some of the metals in the decreasing order of their reactivity is known as the Reactivity Series.

* Hydrogen is also included in this series for the sake of comparison of chemical reactivity.

Oxidation

Oxidation is the process of loss of electrons.

            Or

The process in which oxidation number increases is called oxidation.

Reduction

Reduction is the process of gain of electrons.

            Or

The process in which oxidation number decreases is called reduction.

Redox reactions

The reaction in which, oxidation and reduction takeplace simultaneously is called redox reaction.

REACTIVITY SERIES AND DISPLACEMENT REACTION:

Experiment:

*Prepare some CuSO4 solution in a beaker 1 and ZnSO4 solution in another beaker 2 . Dip a zinc plate in the first beaker and second beaker dip a copper plate.

Oservation:

Beaker 1

Beaker 2.

No change is observed. There is no reaction.

Conclusion: 

* The blue colour of CuSO4 solution is due to the presence of Cu2+ ions. When the Zn plate /rod is dipped in CuSO4 solution, the Cu2+ ions in the solution get deposited at the Zn plate as Cu atoms. 

The chemical reaction is

In this reaction, Zn gets oxidised and Cu2+ gets reduced

ie, oxidation and reduction takeplace simultaneously. This is a redox reaction

* Zn is top of the reactivity series than Cu because Zn has higher reactivity than Cu.

Displacement reaction 

*Metals having high reactivity displace the metals having less reactivity from their salt solution.Such chemical reactions are known as Displacement Reaction

Cu rod dipped in AgNO3(silvernitrate) solution.

The colour of the silvernitrate solution changes to blue and Silver is dipposited on the Cu rod. Because the metal with low reactivity (Ag)is displaced from its solution (AgNO3)by the metal of high reactivity (Cu).

Cu is oxidised and Ag+ is reduced.