capter 6 4 utarid
TRANSCRIPT
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Electrolyte
an electrolyte is a chemical compound which conduct
electric current in a molten state or an aqueous solution
and undergoes chemical change.
electrolyte contain ions which move about freely to
carry electrical charges.
An electrolyte can break down into elements at
electrodes when an electric current flow through it.
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Non- electrolyte
a non-electrolyte is a chemical compund which cannot
conduct electrical current
all states.
there will be no change on a non-electrolyte when an
electric current flow through
it.
non- electrolyte are made from molecules only. There are
no ions which can carry electrical charges in non-
electrolytes.
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Electrolysis of Molten
CompoundsElectrolysis process
electrolysis is the process of breaking down chemical compounds
into their constituent element using electrical current.
Example:
Molten aluminium electric current aluminium + oxygen
oxide
Copper(II) chloride electric current copper + chlorineSolution
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Electrolysis of moltencompounds1) During electrolysis, anions (negative ions) will be pulled
towards the anode (positive electrode). At the anode, anions
will be discharged by releasing electrons to the anode.
2) Cations (positive ions) will be attracted towards the cathode
(negative electrode). at the cathode, cation will be
discharged by accepting electrons from the cathode.
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Predicting products of electrolysis
of molten compounds
Example
Electrolysis of molten zinc iodide, using carbon
electrodes
Solution
Molten zinc iodide, containing and ions.
Anode:
Half equation:
Observation: Purple vapour is released
Product: : Iodine, gas
Cathode:
Half equation:
Observation: grey metal is formed
Product: zinc, Zn metal
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+ -
-- - - - - - -- -
-- --
-- -- --
-- -- - -
Anode Cathode
Iodide ions are selected todischarged
I- Zn+
Electrolysis ofMolten Zinc Iodide
Carbonelectrode
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6.2.1 Electrolysis of Molten Compounds
(i) Moltenlead (II) bromide
Objective:
To investigate the electrolysis of molten lead (II) bromide,
PbBr2
Apparatus: A 6-volt battery, two carbon, C electrodes, four wires with
crocodile clips, a switch, an ammeter, a rheostat, a crucible, a
tripod stand with pipe clay triangle, a Bunsen burner, and
matches.
Materials:
Lead (II) bromide, PbBr2
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CAUTION!
Carry out this activity in a well-ventilated place as bromine
vapour, Br2, is poisonous and pungent.
Procedure:
1 A crucible is filled with solid PbBr2until it is half full.
2 The solid lead (II) bromide is heateduntil it is completely melted.
3 The apparatus as shown in Figure 6.3
is set up.
4 The switch is turned on to allow the
electricity to pass through the molten
lead (II) bromide for about 20 minutes.
5 After that, the switch is turned off and both electrodes are taken
out from the electrolyte. The molten lead (II) bromide is carefully
poured into a beaker using tongs.6 The observation at the anode and cathode are recorded.
Switch
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Substance Does the bulb
lightup?
Observations Conclusion
At anode: A reddish-
brown gas is given off
At cathode: A gray
substance is deposited
Molten lead(II) bromide,
PbBr2
Yes Molten lead(II) bromide,
PbBr2 conducts
electricity. Bromine, Br2
gas is given off at the
anode. Lead, Pb is
deposited at the cathode.
Solid lead(II) bromide,
PbBr2
No No change at electrodes Solid lead(II) bromide,
PbBr2 does not conduct
electricity.
Observation:
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Observation:
Electrode Observation
Anode
Cathode
A brownga
s with
pungent
and c
h
oking smellis released.
A shiny-silver globule is formed atthe bottomof the crucible.
The ammeter shows a reading.
Discussion:1. The molten lead (II) bromide contains .
and that move freely.
lead (II) ions, Pb2+
bromide ions, Br
2. The lead (II) ions move to the while the
bromide ions move to .
cathodeanode
3. At the cathode: Each lead (II) ion is discharged by
electrons to form a lead atom, Pb.
Half equation:
acceptingtwo
Pb2+(l) Pb(s)
+2 0
+ 2e
CD3_50.C2
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Discussion:1. The molten lead (II) bromide contains .
and that move freely.
lead (II) ions, Pb2+
bromide ions, Br
2. The lead (II) ions move to the while the
bromide ions move to .
cathodeanode
3. At the cathode: Each lead (II) ion is discharged by
electrons to form a lead atom, Pb.
Half equation:
acceptingtwo
Pb2+(l) Pb(s)
+2 0
+ 2e
4. At the anode: Each bromide ion is discharged by
electron to form a bromine atom, Br.donating one
Br(l) Br(l)
-1 0
+
e
Half equation:
Br(l) Br2(g)+ Br(l)
2Br(l) Br2(g) + 2e
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Half equation: Pb2+(l) Pb(s)+ 2e
Half equation: 2Br(l) Br2(g) + 2e
Overall equation: 2Br(l) Br2(g) + Pb(s)+ Pb2+(l)
The electrolysis of molten lead (II) bromide producesatthe cathode andatthe anode.
Conclusion:
lead metal
bromine gas
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Exercises: Below are compound in molten state.
Name of
compound
Ions produced Ions that move to
Anode Cathode
Zinc chloride
Magnesiumoxide
Calcium oxide
Aluminium
iodide
Zn2+ & Cl- Cl- Zn2+
Mg2+ & O2- O2- Mg2+
Ca2+ & O2- O2- Ca2+
Al3+ & I- I- Al3+
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Name of
compound
Half equation Products formed at
Anode Cathode Anode Cathode
Zinc chloride
Magnesium
oxide
Calcium
oxide
Aluminium
iodide
Exercises
Cl- Zn2+
O2- Mg2+
O2- Ca2+
I- Al3+
Cl2 Zn
O2 Mg
O2 Ca
I2 Al
Cl- Cl2 + 2e2
-2 0
Zn2+ Zn+ 2e
+2 0
O2- O2 + 2e2 Mg2+ Mg+ 2e
O2- O2 + 2e2 Ca2+ Ca+ 2e
I- I2 + 2e2 Al3+ Al+ 3e
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6.2: Electrolysis of Molten Compounds6.2: Electrolysis of Molten Compounds
1. Identify cation & anion present in compound
2.Identify anion attracted to anode
3. Determine number of electrons involved in discharge (the number of
electrons is equal to the charge on the ion
Product of electrolysis is at the right hand side of chemical equation
Predicting the products of electrolysisPredicting the products of electrolysis
4. Write half-equation of cation
gaining electrons
4. Write half-equation of anion
losing electrons
5. Write balance chemical equation by adding the two half-equations
2.Identify cation attracted to cathode
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+ -Anode Cathode
Carbonelectrode
- -
--
- Molten sodium chloride
compound
1- why does sodium chloride need to be in molten form?
2-name particles in molten sodium chloride.
3- name the ion attracted to the anode and the cathode.4- what can be observed at the anode and the cathode?
5- what are the products formed at the anode and the cathode?
6- write the half equation for the equation occuring at the anode and the
cathode.
Test yourself!