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Class 10, Science, Chapter-1, Lecture-3, Redox Reaction (Notes)

DISPLACEMENT REACTION:

A chemical reaction in which an atom or a group of atoms displaces another atom or a group of atoms from a compound is called a displacement reaction.

Examples:

  • Iron displaces Copper from Copper sulphate solution
    ${\rm{CuS}}{{\rm{O}}_{\rm{4}}}\left( {{\rm{aq}}} \right)\; + \;{\rm{Fe}}\left( {\rm{s}} \right)\;\buildrel {} \over
    \longrightarrow \;{\rm{FeS}}{{\rm{O}}_{\rm{4}}}\left( {{\rm{aq}}} \right)$$ + {\rm{Cu}}\left( {\rm{s}} \right)$
  • Zinc displaces Copper from Copper sulphate solution
    ${\rm{CuS}}{{\rm{O}}_{\rm{4}}}\left( {{\rm{aq}}} \right) + {\rm{Zn}}\left( s \right)\buildrel {} \over
    \longrightarrow {\rm{ZnS}}{{\rm{O}}_{\rm{4}}}\left( {aq} \right)$$$ + {\rm{Cu}}\left( {\rm{s}} \right)$$
  • Lead displaces Copper from Copper chloride solution
    ${\rm{CuC}}{{\rm{l}}_{\rm{2}}}\left( {{\rm{aq}}} \right) + {\rm{Pb}}\left( {\rm{s}} \right)\buildrel {} \over
    \longrightarrow {\rm{PbC}}{{\rm{l}}_{\rm{2}}}\left( {{\rm{aq}}} \right)$$ + {\rm{Cu}}\left( {\rm{s}} \right)$

DOUBLE DISPLACEMENT REACTION:

A chemical reaction in which two compounds react by an exchange of ions to form two new compounds is called a double displacement reaction.

Examples:

  • Sodium sulphate and Barium chloride react to produce white precipitate of Barium sulphate in colourless Sodium chloride.
    ${\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_{\rm{4}}}\left( {{\rm{aq}}} \right) + BaC{l_2}\left( {aq} \right)\buildrel {} \over
    \longrightarrow Ba{\rm{S}}{{\rm{O}}_{\rm{4}}}$$\left( s \right) + 2Na{\rm{Cl}}\left( {{\rm{aq}}} \right)$
  • Sodium chloride and Silver nitrate react to produce white precipitate of Silver chloride in Colourless Sodium nitrate soln.
    ${\rm{NaCl}}\left( {{\rm{aq}}} \right) + {\rm{AgN}}{{\rm{O}}_{\rm{3}}}\left( {{\rm{aq}}} \right)\buildrel {} \over
    \longrightarrow AgCl\left( s \right)$$ + NaN{O_3}\left( {{\rm{aq}}} \right)$
  • Solutions of Lead nitrate and Potassium iodide react to produce yellowprecipitate of Lead iodide and light brown solution of Potassium nitrate.
    ${\rm{Pb}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_2}\left( {{\rm{aq}}} \right) + {\rm{KI}}\left( {{\rm{aq}}} \right)\buildrel {} \over
    \longrightarrow \;{\rm{Pb}}{{\rm{I}}_{\rm{2}}}$$\left( {{\rm{ppt}}} \right) + {\rm{KN}}{{\rm{O}}_{\rm{3}}}\left( {{\rm{aq}}} \right)$

Blue Colour Of Copper Sulphate Solution Is Destroyed When Iron Nail Is Dipped In It.

Reason:

Copper sulphate is blue due to presence of copper ions.

When iron nail is dipped in the copper sulphate solution, iron displaces copper and iron sulphate is formed because iron (Fe) is more reactive than copper (Cu).
${\rm{CuS}}{{\rm{O}}_{\rm{4}}}\left( {{\rm{aq}}} \right)\; + \;{\rm{Fe}}\left( {\rm{s}} \right)\;\buildrel {} \over
\longrightarrow \;{\rm{FeS}}{{\rm{O}}_{\rm{4}}}$$\left( {{\rm{aq}}} \right) + {\rm{Cu}}\left( {\rm{s}} \right)$
Copper ions accept electron and become copper atoms.
So, the blue colour is destroyed due to conversion of copper sulphate into iron sulphate

PRECIPITATE:

A solid product which separates out from the solution during a chemical reaction in aqueous medium is called a precipitate.

PRECIPITATION REACTION:

A chemical reaction in aqueous solution which produces a solid product that separates out from the solution is termed as a precipitation reaction.

Examples:

  • Sodium sulphate and Barium chloride react to produce white precipitate of Barium sulphate in colourless Sodium chloride.
    ${\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\left( {aq} \right) + {\rm{BaC}}{{\rm{l}}_{\rm{2}}}\left( {{\rm{aq}}} \right)\buildrel {} \over
    \longrightarrow \mathop {{\rm{BaS}}{{\rm{O}}_{\rm{4}}}}\limits_{{\rm{white}}\,{\rm{ppt}}{\rm{.}}} $$\left( {\rm{s}} \right) + 2{\rm{NaCl}}\left( {{\rm{aq}}} \right)$
  • Sodium chloride and Silver nitrate react to produce white precipitate of Silver chloride in Colourless Sodium nitrate soln.
    ${\rm{NaCl}}\left( {{\rm{aq}}} \right) + {\rm{AgN}}{{\rm{O}}_{\rm{3}}}\left( {{\rm{aq}}} \right)\buildrel {} \over
    \longrightarrow \mathop {{\rm{AgCl}}}\limits_{{\rm{white}}\,{\rm{ppt}}{\rm{.}}} $$\left( {\rm{s}} \right) + {\rm{NaN}}{{\rm{O}}_{\rm{3}}}\left( {{\rm{aq}}} \right)$

OXIDATION REACTION:

A chemical reaction which involves addition of oxygen or removal of hydrogen or removal of electrons is termed as oxidation reaction.

Examples:

  • Addition of Oxygen
    ${\rm{Mg}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow 2{\rm{MgO}}({\rm{s}}){\rm{  }}$
    $2{\rm{Cu}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\,\buildrel {} \over
    \longrightarrow 2{\rm{CuO}}({\rm{s}}){\rm{  }}$
  • Removal of Hydrogen
    ${{\rm{H}}_{\rm{2}}}{\rm{S}}({\rm{g}}) + {\rm{C}}{{\rm{l}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow 2\,{\rm{HCl}}({\rm{s}}) + {\rm{S}}\,({\rm{g}}){\rm{ }}$
  • Removal of electron
    ${\rm{Na}}\buildrel {} \over
    \longrightarrow N{a^ + } + \,{{\rm{e}}^ - }{\rm{ }}$

REDUCTION REACTION:

A chemical reaction which involves removal of oxygen or addition of hydrogen or addition of electrons is termed as reduction reaction.

Examples:

  • Removal of Oxygen
    ${\rm{ZnO}}({\rm{s}}) + {\rm{C}}({\rm{s}})\buildrel {} \over
    \longrightarrow {\rm{Zn}}\,({\rm{s}}) + {\rm{CO}}({\rm{g}}){\rm{  }}$
    ${\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}(s) + 3{\rm{CO}}({\rm{g}})\buildrel {} \over
    \longrightarrow 2{\rm{Fe}}({\rm{s}}) + 3{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}}){\rm{  }}$
  • Addition of Hydrogen
    ${{\rm{H}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}({\rm{g}})\buildrel {} \over
    \longrightarrow {{\rm{H}}_{\rm{2}}}{\rm{S}}\,({\rm{g}})$
    ${{\rm{H}}_{\rm{2}}}{\rm{S}}({\rm{g}}){\rm{C}}{{\rm{l}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow {\rm{2HCl}}({\rm{s}}) + {\rm{S}}\,({\rm{g}})$
  • Addition of electron
    ${\rm{Cl}} + {{\rm{e}}^ - }\buildrel {} \over
    \longrightarrow {\rm{C}}{{\rm{l}}^ - }$

REDOX REACTION:

A chemical reaction in which oxidation and reduction occur simultaneously is called a redox reaction.

Examples:

EFFECTS OF OXIDATION:

  1. Corrosion
  2. Rancidity