Your SlideShare is downloading. ×
Redox Reactions
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Saving this for later?

Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime - even offline.

Text the download link to your phone

Standard text messaging rates apply

Redox Reactions

17,254
views

Published on

Oxidation and Reduction - What are they?

Oxidation and Reduction - What are they?

Published in: Education, Technology, Business

1 Comment
9 Likes
Statistics
Notes
No Downloads
Views
Total Views
17,254
On Slideshare
0
From Embeds
0
Number of Embeds
7
Actions
Shares
0
Downloads
0
Comments
1
Likes
9
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. REDOX REACTIONS Oxidation and Reduction
  • 2. Objectives
    • Define oxidation and reduction (redox) in terms of oxygen / hydrogen gain/loss.
    • Define redox in terms of electron transfer and changes in oxidation state.
    • Describe the use of aqueous potassium iodide and acidified potassium dichromate (VI) in testing for oxidising and reducing agents from the resulting colour changes
  • 3. Redox reactions around us…
    • Combustion of gasoline
    • Browning of a freshly cut apple
    • Corrosion of metals
    • Photosynthesis
    • Removal of stains at home
    • Lightening of hair colour (bleaching)
  • 4.  
  • 5. Introduction
    • Redox reactions involve a transfer of electrons.
    • Oxidation is always accompanied by reduction
  • 6. What is oxidation? A substance is oxidised if one the following happens after a reaction: It gains oxygen or It loses hydrogen or It loses electrons or It increases its oxidation state.
  • 7. Oxidation — Gain of Oxygen 2Ca(s) + O 2 (g)  CaO(s) By the end of the reaction, calcium has gained oxygen. Calcium has been oxidised to calcium oxide . This process is called oxidation .
  • 8. Oxidation — Gain of Oxygen CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O( l ) The carbon atom in methane has gained oxygen and has been oxidised to carbon dioxide . The hydrogen atom in methane has also gained oxygen . Hydrogen has been oxidised to water.
  • 9. Oxidation — Loss of Hydrogen A substance is oxidised if it loses hydrogen. 2NH 3 (g) + 3CuO(s)  N 2 (g) + 3Cu(s) + 2H 2 O(g) Ammonia has lost hydrogen. It has been oxidised to nitrogen.
  • 10. Oxidation — Loss of Electrons When a substance loses electrons during a reaction, it is oxidised. Oxidation reactions can take place even if there is no oxygen or hydrogen present .
        • Mg(s) + C l 2 (g)  MgC l 2 (s)
    Look at the equation above. In the next slide, you see how electrons are lost in this reaction.
  • 11. Oxidation — Loss of Electrons Mg  Mg 2+ + 2e – Each magnesium atom loses 2 electrons to form a magnesium ion.
      • In this reaction, magnesium atoms has been oxidised to form magnesium ions.
    Mg(s) + C l 2 (g)  MgC l 2 (s)
  • 12. Oxidation — Loss of Electrons The copper atom has been oxidised to the copper(II) ion. In the reaction Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s) which substance is oxidised? The ionic equation for this reaction is Cu(s) + 2Ag + (aq)  Cu 2+ (aq) + 2Ag(s)
      • Each copper atom loses 2 electrons and becomes a copper(II) ion.
  • 13. Oxidation — Increase in Oxidation State The oxidation state is the “ charge ” an atom of an element would have if it existed as an ion in a compound (even if it is actually covalently bonded). The oxidation state is also known as oxidation number .
  • 14. Various Definitions of Oxidation & Reduction Redox Oxidation Reduction Gain in Oxygen Loss in Hydrogen Loss in Electron (s) Loss in Oxygen Gain in Hydrogen Gain in Electron (s ) Increase in Oxidation State Decrease in Oxidation State 1 2 3 4
  • 15. Mnemonics for Redox – OIL - RIG OIL - RIG : Oxidation is Loss – Reduction is Gain Redox Oxidation Reduction Gain in Oxygen Loss in Hydrogen Loss in Electron (s) Loss in Oxygen Gain in Hydrogen Gain in Electron (s )
  • 16. Test your understanding
  • 17.
    • For the following reactions, identify which species is oxidized and which species is reduced :
    • PbO(s) + H 2 (g)  Pb(s) + H 2 O(g)
    • Answer: PbO [R], H 2 [O]
    • Fe 2 O 3 (s) + 3CO(g)  2Fe(s) + 3CO 2 (g)
    • Answer: Fe 2 O 3 [R], CO [O]
    • Mg(s) + Cl 2 (g)  MgCl 2 (s)
    • Answer: Mg [O], Cl 2 [R]
  • 18.
    • For the following reactions, identify which species is oxidized and which species is reduced:
    • 2NH 3 (g)+ 3Cl 2 (g)  N 2 (g) + 6HCl (g)
    • Answer: Cl 2 [R], NH 3 [O]
    • SnO 2 (g) + 2C (s)  Sn (s) + 2CO (g)
    • Answer: SnO 2 [R], C [O]
    • WO 3 (s) + 3H 2 (g)  W (s) + 3H 2 O (g)
    • Answer: WO 3 [R], H 2 [O]