redox presentation 11 july 2011
DESCRIPTION
basic concept in chemistryTRANSCRIPT
REDOX1.A.DEFINATION
Transfer of electrons Oxidation is
reduction is
PROCESS WHERE ELECTRON IS RELEASED
PROCESS WHERE ELECTRON IS GAINED
change in oxidation numberOxidation is
reduction is
PROCESS WHERE OXIDATION NUMBER INCREASE
PROCESS WHERE OXIDATION NUMBER DECREASE
b.Calculate the oxidation number of i.Chromium in K2Cr2O7
ii. Chlorine in ClO4-
iii.Oxygen in H3O+.
2(+1) + 2x +7(-2) =0. , Cr = +6
x +4(-2) =-1. , Cl= +7
3(+1) +x =+1. , O= -2
c.IUPAC nomenclature
i.K2CrO4
ii.MgSO4
Potasium Chromate (VI)
Magnesium sulphate(VI)
iii.HNO3
iv.HNO2
nitric acid (V)
Nitric acid (III)
d. Redox & non redox reaction. reasonsi. Zn + CuSO4 Cu + ZnSO4
ii. ZnCO3 ZnO + CO2
Redox reaction because the oxidation number of Zn Change from 0 to +2
Non Redox reaction because the oxidation number of Zn no change,( from +2 to +2)
B) Br2 + 2KI I2 + 2KBr i.name of this reaction
ii.change in oxidation number of bromine
iii. change in oxidation number of iodine
Displacement of halogen
From 0 to -1
From -1 to 0
iv.half equation for• Oxidation reaction.
• Reduction reaction
• Write the overall equation
2I- I2 + 2e
Br2 + 2e 2Br-
Br2 + 2I- 2Br- + I2
Question 2
Iron(II) chloride reacts with chlorine in a redox reaction
Name the reaction above
• CHANGE OF IRON(II) ION TO IRON(III) ION
• REDOX (TYPE OF REACTION)
Write out the rough equation first to show the products and the
reactants
2FeCl2 + Cl2 2FeCl3
Place arrows to show oxidation reaction and reduction reaction on your answer on your answer in b)
above
2FeCl2 + Cl2 2FeCl3
reduction
oxidation
What substance is oxidized and why?
• Iron (II) ions, oxidation number of iron
increase from +2 to +3
What substance is reduced and why?
• Chlorine, because oxidation number of chlorine decrease from
0 to -1
Write the half equation for oxidation
Fe2+ Fe3+ + e
Write the half equation for reduction
Cl2 + 2e 2Cl-
Write the overall reaction
2Fe2+ + Cl2 2Fe3+ +
2Cl-
What is the oxidizing agent? And why
Chlorine water,
because it oxidised iron(II) ions to iron(III) ions
What is the reducing agent? And why
Iron(II) ions,
because it reduced chlorine
to chloride ions
State 2 observations in this experiment
• Green solution turns brown
Describe how you would confirm the presence of the product, that is
iron(III) ion
• Add a few drops of NaOH solution, brown precipitate is formed
State another substance that can replace chlorine in the above
experiment
Any oxidising agent
Bromine water //
acidified KMnO4 //
acidified K2Cr2O7
a) Which electrode behave as negative electrode? Why?
- +
3.
a) Which electrode behave as negative electrode? Why?
A because iodide ions undergoes oxidation where it lose electrons,
the electrons are negatively charged causing it to be negative electrode
b) Draw direction for electron flow in the outer circuit
c) Write out the rough equation first to show reactants and the products
d) Put arrows on your equation above to show oxidation reaction and reduction reaction on your answer in c) above
32
272 22 CrIOCrI
OXIDATION
REDUCTION
e) What substance is oxidized? Explain your answer in terms of electron transfer
Iodide ions
because it lose electron
f) What substance is reduced? Explain your answer in terms of electron transfer
Dichromate ions
because it accept electrons
g) Write half equations for:i)Oxidation
ii)Reduction
eII 22 2
OHCr
eHOCr
23
272
72
614
h) Write overall equation
6I- + Cr2O72- + 14H+
2Cr3+ + 7H2O + 3I2
i) State your observations during the experiment ati)Rod A
ii)Rod B
Dark brown solution formed
Orange solution turns to green solution
j)How do you test the presence of iodine formed at rod A?
OR
Add 2 cm3 tetrachloromethane to iodine solution, shake well then purple solution formed at lower layer
Add a few drops of starch solution, a blue-black solution formed
• Test tube C, D. Presence of Fe 2+
• In C and D, silver and lead are less electropositive than iron.
• So,iron nail (Fe) is oxidised to Fe 2+.
• In test tube E, iron nail also
oxidised but takes longer time
After 3 days, which test tubes show blue colour?, why?
Which test tubes show pink colour? Why?
• Test tube A and B.
• Presence of OH-
• Because Mg and Zn are more electropositive than Fe.
• So, Mg atom and Zn atom will lose electrons
• oxygen and water gain these electrons to form OH- This cause the pink colour of phenolphthalein
What is the function of the jelly solution?
• To trap the colour formed during corrosion process
Which of the above metals prevent rusting of iron nails?
• Metals above iron in ECS Magnesium and Zinc metals.
Which of the above metals increase the rusting of iron
• Metals below iron in ECS
• Lead metal and silver metal
Why does the iron surface at the centre of water droplet behave as anode (negative electrode)?
Because here iron atom release electron
Why does the iron surface at the edge of water droplet behave as
cathode( positive electrode)?
• Because oxygen and water gain the electrons here.
What happen at the anode?
• Iron atom loses electron to form iron (II) ions.
• So Oxidation occur.
Write half equation at the anode
Fe Fe 2+ + 2e
Where does the iron(II) ions formed from the reaction go to?
Iron (II) ions dissolve in water
Where does the electrons released by the metal iron go
to?• Electron moves to the edge of
water droplet ( cathode)
What happens at the cathode?
At cathode, electrons are received by oxygen and water molecules to form hydroxide ions
Write half equation at the cathode
• O2 + 2H2O +4e 4OH-
Write equations to form rust when iron(II) ion formed at the anode combine with hydroxide ions formed at the cathode, • Fe 2+ + 2OH- Fe(OH)2
Fe(OH)2 Fe2O3.xH2O