oxidation and reduction

• Oxidation is defined as gain of oxygen atoms or loss of hydrogen atoms by an element
• Acetylene is commercially used for cutting and welding metals
• When acetylene burns, it produces a very hot flame known as oxy-acetylene flame
• The reaction for acetylene burning is: C2H2 + O2 → CO2 + H2O
• Coal is burned in thermal power stations to produce electricity
• The reaction for coal burning is: C + O2 → CO2
• oxidation that does not involve burning is rusting. In rusting the following reaction takes place

  Fe+O2 --> Fe2O3
• A process that involves the loss of electrons by an element is called oxidation.
• following reaction takes place when sui gas burns

  CH4+O2 --> CO2+H2O+heat
• Group 1A lose 1 electron to form cation 


  Group 2A lose 2 electrons to form cation
• group 6A gain two electrons to form anion
• group 7A gain one electron to form anion
• the symbol used to represent the state of matter is (g) for gaseous, (l) for liquid, (aq) for aqueous solution and (s) for solid
• the group number tells us how many electrons are lost or gained during reactions
• the most reactive metals are sodium, potassium, lithium and magnesium
• reduction is gaining of electrons
• in redox reactions both oxidation and reduction take place at the same time
• A process that involves the gain of electrons by a substance is called reduction.
• Oxidising agents cause other substances to lose electrons.
• Reducing agents donate electrons to other substances.
• what is oxidation state or oxidation number?

  The oxidation state or oxidation number is defined as the number of charges an atom will have in a molecule or compound.
• what is oxidation?

  gain of oxygen

  loss of hydrogen

  loss of electrons

  increase in oxidation number
• what is reduction?

  gain of hydrogen

  loss of oxygen

  gain of electrons

  decrease in oxidation number
• what are the rules for assigning oxidation state?

  1. uncombined or free elements are always zero
  2. in simple ions oxidation state is same as their charge
  3. in complex ion the algebraic sum of the oxidation state of an element is not zero
  4. in a compound the algebraic sum of the oxidation state of an element is zero
• what is reducing agent?

  a reducing agent oxidizes itself and reduces the other element.
• what is oxidizing agent?

  an oxidizing agent reduces itself and oxidizes the other element.
• anion and cation combine to form ionic compound
• calcium and chlorine contain neutral atoms.
• metals are recovered from their ores through redox reactions.
• most metals are found in nature as oxides or sulphide ores.
• purified metal oxides are reduced to free metals by using a reducing agent.
• what does extraction of iron involve?

  the chemical reaction of Hematite ore by coke in a blast furnance.
• lead and zinc metals occur naturally as sulphide ores.
• how many types of electrochemical cells are there?

  two types, galvanic and electrolytic.
• what is electrolytic cell?

  an electrochemical cell that uses electrical energy to derive chemical reaction is known as electrolytic cell.
• what is galvanic cell?

  an electrochemical cell that converts chemical energy to electrical energy is known as galvanic cell.
• what is electrolyte?

  a substance that conducts electricity when it is dissolved in water or in the molten state is known as an electrolyte.
• what is non electrolyte?

  a substance that cannot conduct electricity when dissolved in water or in the molten state is known as non electrolyte.
• what does an electrolytic cell consist of?

  1. A vessel containing a electrolyte
  2. two inert electrodes
  3. a battery
• at anode is electrolytic cell: X- --> X+1e