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Redox Notes

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Chemistry IGCSE
Redox
Name: _______________________________
REDUCTION
1
Date: ________
Redox OXIDATION
A Closed System
A chemical reaction is a closed system whereby a substance can only be oxidised
when there is another substance getting reduced
A reaction in one substance is always in the expense of another substance
A
+
C
B
+
D
oxidised reduced
2
Oxidising and Reducing Agents
A reaction in a substance is caused by another
Eg. When A undergoes oxidation, B is the oxidising agent
When B undergoes reduction, A is the reducing agent
OXIDISING AGENT:
Causes oxidation of another substance,
itself is reduced.
3
REDUCING AGENT:
Causes reduction of another substance,
itself is oxidised.
Defining Redox 1 - Transfer of oxygen atoms
OXIDATION: Gain of oxygen
REDUCTION: Loss of oxygen
loses oxygen to become Cu
2 CuO
+
Mg
à
MgO
+ Cu
OXIDATION: Mg (Reducing agent)
REDUCTION: CuO (Oxidising agent)
gains oxygen to become MgO
4
Defining Redox 2 - Transfer of electrons
OXIDATION: Loss of electrons
REDUCTION: Gain of electrons
loses electron to become Na+
2 Na
+
Cl2
à
2 NaCl
OXIDATION: Na (Reducing agent)
REDUCTION: Cl2 (Oxidising agent)
gains electron to become Cl-
5
Writing Half-equations
Ionic half-equations shows oxidation and reduction taking place in a reaction
separately
Oxidation (Loss of electrons)
a) Metals
!" → !"% + '(
b) Non-metallic ions
) *)( → *) + + '(
c) Hydroxide ions
+ *.( → *)
+
Reduction (Gain of electrons)
a) Metallic ions
,-)% + ) '( → ,-
) .) * + + '(
b) Non-metals
2 Cl,/) + )'( → ,/
)
c) Hydrogen ions
. % + ) '( → .)
1
Prepared by Chermaine Lim (2019)
Chemistry IGCSE
Redox
1
For the following reactions, identify the substance that is oxidised, reduced and the respective
agents in terms of gain/loss of electron.
a)
Mg
+
F2
MgF2
à
Oxidised
Oxidising Agent
b)
2 Na
+
F2
+
2 KI
à
Oxidised
F2
K+ Cl-
2 KCl
2
F2
Reducing Agent
+
Reduced
KI
Reducing Agent
or
Na
I2
Cl2
Oxidising Agent
d)
Mg
Reduced
Na
K+ I-
F2
2 NaF
à
Oxidising Agent
Cl2
Reducing Agent
F2
Oxidised
c)
Reduced
Mg
I-
KI
or
I-
Cl2
CuO + Zn à ZnO + Cu
Oxidised
Zn
Reduced
Oxidising Agent
CuO
Reducing Agent
CuO
Zn
Write the half equations for the following situations:
a)
Magnesium metal becomes magnesium ion by losing electrons.
oxidised
Magnesium metal is _________________.
Mg —> Mg2+
b)
+
2e
Copper ion gains electrons to become copper metal.
Copper ion is _________________.
reduced
Cu2+
c)
+
2e
—>
Cu
Hydrogen ions gain electron to become hydrogen gas.
Hydrogen ions are _________________.
d)
Chloride ions become chlorine gas by losing electrons.
Chloride ions are __________________.
e)
Bromine molecules gains electron to form bromide ions.
Bromine molecules are _________________.
f)
Aluminium metal become aluminium ions by losing electrons.
oxidised
Aluminium metal is __________________.
Al —> Al3+
+
3e
2
Prepared by Chermaine Lim (2019)
Chemistry IGCSE
Redox
3
Identify the substances from the list below whether they can take part in oxidation or reduction.
Na
Br-
I2
Pb
Mg2+
I-
Cu2+
Pb2+
Cl-
Mg
OH-
H+
Cu
Fe3+
Na+
Cl2
Oxidation
Na
I-
Pb
Cl-
Mg2+
Cu
OH-
Br-
6
Reduction
Cu2+
I2
Mg
Pb2+
Fe3+
H+
Na+
Cl2
Determining Oxidation States/Numbers
Charge an element would have if it existed in a compound
To
a.
b.
c.
determine O.S of substances:
Elements & Molecules à Always zero
Atoms in a compound à Sum of O.S of all atoms is zero
Some atoms have fixed O.S. :
Li, Na, K
F
O
+1
-1
H
-2
+1
d. Ions à Follows the charge of the ion
e. Atoms in a polyatomic ion à Sum of O.S of all atoms in a polyatomic ion follows its
charge
f. IUPAC naming gives the O.S. of the transition metals
7
Defining Redox 3 - Increase/Decrease of O.S
OXIDATION: Increase
REDUCTION: Decrease
+1
2HCl
+
spectator ion
1
Mg
à
0
-1
+2
0
-1
MgCl2
+
* follow charge of metal
OXIDATION: Mg (Reducing agent)
REDUCTION: H+ (Oxidising agent)
H2
HCl
Give the oxidation state for the following substances:
a)
Elements/Ions
Element/Ion
Na
O2
b)
Oxidation State
Element/Ion
C
0
O2-
0
Oxidation State
0
-2
Atoms in Compounds
Element in Compound
Oxidation State
Element in Compound
Oxidation State
PbO2
+4
CuO
+2
Na2SO3
+4
K2CrO4
+6
KMnO4
MnO2
+7
3
=4
Prepared by Chermaine Lim (2019)
Chemistry IGCSE
Redox
2
For the following reactions, identify the substance that is oxidised, reduced and the respective
agents in terms of increase/decrease of oxidation state.
a)
b)
1
3 CuCl2
+
2 Al
à
3 AlCl3
+
2 Cu
Oxidised
Reduced
Oxidising Agent
Reducing Agent
Cl2
+
2 KI
à
2 KCl
+
I2
Oxidised
Reduced
Oxidising Agent
Reducing Agent
A piece of zinc is immersed in a blue solution of copper (II) sulfate.
a)
Which is the more electropositive metal, zinc or copper?
b)
Write a balanced chemical equation to show the redox reaction occurring.
4
Prepared by Chermaine Lim (2019)
Chemistry IGCSE
Redox
c)
i)
ii)
d)
i)
ii)
e)
Identify the substance going through oxidation.
Zinc
Write the half equation for the oxidation reaction.
Zn —> Zn2+
+
2e
Identify the substance going through reduction.
CuSO4
Write the half equation for the reduction reaction.
Cu2+
+
2e
—>
Cu
A piece of silver in immersed in copper (II) sulfate solution now. Compare this reaction with
that of zinc. Explain your answer.
No changes. silver is less reactive compared
to copper.
2
A piece of magnesium is immersed in a zinc nitrate solution.
a)
Which is the more electropositive metal, zinc or magnesium?
magnesium
b)
Write a balanced chemical equation to show the redox reaction occurring.
c)
i)
d)
Mg +
Identify the substance going through oxidation.
Mg
ii)
Write the half equation for the oxidation reaction.
i)
Identify the substance going through reduction.
ii)
e)
Zn(NO3)2 —> Mg(NO3)2 + Zn
Mg —>
Mg2+ + 2e
Zn(NO3)2
Write the half equation for the reduction reaction.
Zn2+ + 2e —> Zn
A piece of copper in immersed in zinc nitrate solution now. Compare this reaction with that
of magnesium. Explain your answer.
No changes. Copper is less reactive than zinc.
3
Chlorine gas is bubbled into a solution of potassium bromide.
a)
Which is the more electronegative halogen, chlorine or bromine?
Chlorine
5
Prepared by Chermaine Lim (2019)
Chemistry IGCSE
Redox
b)
c)
d)
Write a balanced chemical equation to show the redox reaction occurring.
Cl2 +
i)
2KCl + Br2
Identify the substance going through oxidation.
KBr
ii)
Write the half equation for the oxidation reaction.
i)
Identify the substance going through reduction.
ii)
e)
2KBr —>
2Br-
—> Br2 + 2e
Cl2
Write the half equation for the reduction reaction.
Cl2
+ 2e —> 2Cl-
Iodine vapour is bubbled into the potassium bromide solution now. Compare this reaction with
that of chlorine. Explain your answer.
No changes. Iodine is less reactive than
chlorine
4
Fluorine gas is bubbled into a solution of potassium chloride.
a)
Which is the more electronegative halogen, chlorine or fluorine?
b)
Write a balanced chemical equation to show the redox reaction occurring.
c)
i)
Identify the substance going through oxidation.
ii)
Write the half equation for the oxidation reaction.
i)
Identify the substance going through reduction.
ii)
Write the half equation for the reduction reaction.
d)
6
Prepared by Chermaine Lim (2019)
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