Chemical Reactions and Equations Blog 5


Dear Learners,

We are continuing our blog on Type of Chemical Reaction.

We have already discussed about combination reaction, decomposition reaction and single displacement reactions in our previous blog.

Today, we will be learning about double displacement reaction, oxidation-reduction (Redox reaction) and Effects of Oxidation reaction in our everyday life.

At the end of topic, the learners will be able to
(i) define double displacement reaction.
(ii) state chemical reactions related to double displacement reaction.
(iii) define oxidation and reduction reaction.
(iv) state chemical reactions related to oxidation-reduction reaction.
(v) explain corrosion and rancidity.

So, let us start......

4. Double Displacement reaction:
Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Example 1: Refer activity 1.10 when sodium sulphate reacts with barium chloride it forms barium sulphate and sodium chloride.

 
        Na2SO4      +         BaCl2         -->   BaSO4             +     2NaCl

The white precipitate BaSO4 is formed by the reaction of SO4-2 and Ba2+ . The other product formed is sodium chloride which remain in the solution.

Few more examples
Example 1.     Silver nitrate is added to sodium chloride it forms white precipitate of silver chloride is formed and sodium nitrate.
        AgNO3        +             NaCl          -->   AgCl           +    NaNO3


Example 2. Barium chloride reacts with copper sulphate to form white ppt of barium sulphate and copper chloride.

   BaCl2          +            CuSO4            -->          BaSO4        +       CuCl2



Oxidation: (i) The addition of oxygen to a substance is called oxidation.


4Na    +     O2       -->  2Na2O
2Mg   +     O2       -->  2MgO
S         +     O2       -->  SO2
C         +     O2       -->  CO2

(ii) The removal of hydrogen from a substance is called oxidation.

4HCl    +    MnO2   -->  MnCl2   +    2H2O    +  Cl2               …oxidation of HCl

H2S      +    Cl2       -->  2HCl       +   S                               …oxidation of H2S
8HCl     +    Pb3O4  --> 3PbCl2   +   4H2O     +   Cl2             …oxidation of HCl

refer activity 1.11


Reduction: (i) Reduction is a process of removal of oxygen
CuO      +     H2     -->    Cu    +   H2O     …reduction of CuO
CuO      +    CO      -->    Cu    +   CO2    …reduction of CuO

https://www.youtube.com/watch?v=Ju1lNZxxo8M

https://www.youtube.com/watch?v=iAiiHAGjC48
                                      
(ii) Reduction is a process of addition of hydrogen.
 2H2       +     O2    -->  2H2O                  …reduction of oxygen
 H2         +     Cl2    --> 2HCl                    …reduction of chlorine
2NH3     +     3Cl2   -->   N2   +    6HCl     … reduction of Cl2

Effects of Oxidation Reactions in Everyday Life
1. Burning of a fuel in oxygen in a redox reaction.
2. Corrosion of metals is a redox reaction.
3. Rusting of iron is a redox reaction.
4. Metabolism of glucose in our body is a redox reaction.
5. Removal of strain by oxalic acid is a redox reaction.
6. Formation of rancid fatty foods is redox reaction.

Let us now discuss corrosion and rancidity in detail
1. Corrosion:The process of formation of undesired compounds on the surfaces of metallic objects is called corrosion of metals.

Corrosion of Iron (Rusting of Iron): A brown deposit of rust on the surface of iron objects is due to corrosion called rusting of iron.  Red is a reddish brown powder its general formula Fe2O3. xH2O

                   Fe +  O2  + H2O      -->   Fe2O3.xH2O


Condition for necessary Rusting: (i) Water and air both. (ii) Presence of salt and dissolved gases speeds up rusting.


Corrosion of Copper: A green deposit of basic carbonate on the surface of copper is due to corrosion. In this process copper is attacked by moist air and a green layer of basic carbonate is deposited on its surface.
                   
2Cu    +    O2   +  CO2    +   H2O   -->    Cu(OH)2.CuCO3

Corrosion of Aluminium: The layer of insoluble aluminium oxide (Al2O3) is formed on the surface aluminium.

                             4Al   + 3O2    -->    2Al2O3


Corrosion of Silver: Silver is tarnished when exposed to atmospheric air for a long period. This occurs because hydrogen sulphide gas (H2S) present in the polluted air attacks the metal and forms a black mass of silver sulphide (Ag2S).
Advantages of Corrosion:
Corrosion of aluminium prevents it from further corrosion as a thin layer of aluminium oxide covers the surface of the object.
Iron objects which fall on the earth are destroyed by rusting and thus iron oxide passes into soil which is useful for crops.

Rancidity: 
Deterioration of fatty and oily foods and oily foods by oxidation producing unpleasant smells and tastes in them is called rancidity. It is caused by oxidation. In the process of oxidation the hydrogen ion of fatty acid molecules is replaced by oxygen ion. This oxidation makes the molecules unstable and it decomposes into small fragments losing its taste.
Retardation of Oxidation of fatty Foods:
1. By the use of airtight and light-protecting packaging.
2. By the use of spices.
3. By the use of antioxidants such as vitamin E and vitamin C.
4. By the use of nitrogen gas in the pouches of food item as it prevent contact with oxygen.
Home Assignments

1. Complete your notebook.

2. In the reaction represented by the following equation:

CuO (s) + H2(g) → Cu(s) + H2O
(i) Name the substance oxidized   (ii) Name the substance reduced
(iii) Name the oxidizing agent                  (iv) Name the reducing agent


3. When copper powder is heated strongly in air, it forms copper oxide. Write a balanced chemical equation for this reaction. Name (i) substance oxidized, and (ii) substance reduced.

4. When a magnesium ribbon is heated, it burns in air to form copper oxide. Write a balanced chemical equation for this reaction. Name (i) substance oxidized, and (ii) substance reduced.

5. In the following reaction between lead sulphide and hydrogen peroxide:
PbS (s) + 4H2O­2 (aq) → PbSO4 (s) + 4H2O (I)
(i) Which substance is reduced?
(ii) Which substance is oxidized?

6. Explain the term ‘corrosion’ with an example.
7. Which chemical reaction is involved in the corrosion of iron?
8. Write a chemical equation to show the process of corrosion (or rusting) of iron.
9. Which term is used to indicate the development of unpleasant smell and taste in fat and oil containing foods due to oxidation?

10. Explain the term ‘rancidity’

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  2. Good morning sir
    Sarim

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  3. Good morning ma'am
    Riyansh gautam
    XD

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