assignment 5 simulation modelling
TRANSCRIPT
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SIMULATION [SKP6024 - Technology And Innovation In Teaching And Learning Chemistry]
SKP 6024
TECHNOLOGY AND INNOVATION IN TEACHING
AND LEARNING CHEMISTRY
GROUP ASSIGNMENT:
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ELECTROLYSIS
Teachers Guide / Chemistry Form 4 / Simulation
SCIENTIFIC CONCEPT
Conductor
A conductor is a substance which conducts electricity but is not chemically changed during theconduction.
InsulatorsA non-conductor is a substance which does not allow the passage of electricity. Sometimes these
non-conductors are used to protect something from electricity. They are then called insulators.
Electrolytes
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Factor Affecting Electrolysis
There are 3 factors that may influence the selective discharge of ions during the electrolysisof an aqueous solution.
When more than one type of ions move towards the electrode during electrolysis, only onetype of ion is selected to be discharged.
Selective discharge only occur in aqueous solution because it usually has more than one typeof ions attracted to the anode or cathode.
The selection of ion for discharge depends on three factors :i) The position of ions in the Electrochemical Series (normally in dilute solution and
inert electrodes are used)
ii) The concentration of electrolyte / ions (normally in concentrated solution andinert electrodes are used)
iii) The types of electrode (when active metal electrode is used)
(I) The position of ions in the Electrochemical Series
When electricity is conducted in dilute solution used inert electrodes, the cations oranions in the lower position in the Electrochemical Series will be selectively discharged.
Electrochemical Series
Cation Anion
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The chart above lists the ions in order of difficulty of discharge The ions at the top of the list is more difficult to be discharged, but as we go down the
table, their become easier to be discharged. For example, Cu+
easier to be discharged
compare with Ag+
and OH-is easier to be discharged compare with I
-.
This series is called Electrochemical series The lower the ion in the electrochemical series, the easier the ion to be discharged during
electrolysis.
Example :
Electrolysis of 0.1 mol dm-3
sulphuric acid, using carbon electrodes.
Apparatus set-up :
carbon electrodes
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Name of the products at the
anode and cathodeOxygen Hydrogen
Observations Gas bubbles are released Gas bubbles are released
Confirmatory test
[methodandobservations of
the test]
Insert glowing wooden splinter
into the test tube
When the ligthed wooden
splinter is placednear the mouth
of the test tube
Glowing wooden splinter is
lighted up
A pop sound is produced
(II) Concentration of electrolyte
When electrolysis is carried out using inert electrodes and concentrated solutions, ions that aremore concentrated will be selected to discharge, but this is only true for halide ions; which are
Cl-, Br
-and I
-.
Example:
Electrolysis of :
Set I : 0.001 mol dm-3
hydrochoric acid, HCl(aq)
Set II : 2.0mol dm-3
hydrochoric acid, HCl(aq)
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The electrolyte ionisation
equation
HCI H+
+ CI-
H2O H
+
+ OH
-
Ions exist in electrolyteH
+, CI
-, OH-
Set I : 0.001 mol dm-3diluteHCl Set II : 2.0 mol dm
-3concentratedHCl
The ions that are move to
the cathodeH
+ H
+
Ions that are selectively
discharge H+
H+
Discharge equation at the
Cathode
2H+ + 2e H2 2H+ + 2e H2
Name of theproduct at
the CathodeHydrogen gas Hydrogen gas
The ions that move to the
AnodeOH
- CI-
OH- CI
-
Selective ion OH
-
CI
-
Discharge equation at the
Anode
4OH- 2H2O + O2 + 4e 2CI-
CI2 + 2e
Name of the product at
the AnodeOxygen gas Chlorine gas
Observation Gas bubbles are released Greenish yellow gas is released
Confirmatory test for
product form at anode*.[methodandobservation
f th t t ]
Insert glowing wooden splinter
into the test tube
A damp blue litmus paper placed near
the mouth of the test tube
Glowing wooden splinter is
li ht d
The gas changed the damp blue litmus
t d d th bl h d it
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(III) Types of electrode
There are two types of electrode :
Inert electrodeAn electrode that acts as a conductor of current only and does not undergoany chemical
changes.Normally are made ofcarbonorplatinum. These electrodes do not participate in
an electrolysis but merely provide a surface for the release of electrons.
Non-inert/ active electrodeAn electrode that not only acts as a conductor of current but also undergoes chemical
changes. During the electrolysis, the metal anode will corrode while the reaction at the
cathode is similar to the reaction at carbon electrode. Consist of metal anodes such as
copper, silver and nickel.
Example :
Set I : Electrolysis of 0.02 mol dm-3
silver nitrate solution using carbon electrodes
Set II : Electrolysis of 0.02 mol dm-3
silver nitrate solution using silver electrodes
Apparatus set-up :
Set I : Carbon electrodes Set II : Silver electrodes
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Set I : Carbon electrodes Set II : Silver electrodes
The ions that move to the
cathodeAg
+ H+ Ag
+ H+
Discharge equation at the
cathodeAg+ + e Ag Ag+ + e Ag
Name of the product at
the cathodeSilver solid Silver solid
The ions that move to the
anodeOH- NO2-3 OH
- NO2-3
Discharge equation at the
anode
4OH- 2H2O + O2 + 4e Ag Ag+ + e
Name of the product at
the anodeOxygen Silver solid
Observations
at the
Cathode Grey shiny solid deposited Grey shiny solid deposited
Anode Gas bubbles are released Anode becomes thinner
UNIQUE FEATURE OF THIS ACTIVITY
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ENGAGING
Figure 1
1. What do you understand about Figure 1 diagram?2. Give 3 factors that can affect light in the bulb3. What the different between electrolyte and non electrolyte?
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EMPOWERING
1. Electrolysis is the dissociation of an electrolyte into ions at the electrodes by the passage of
electric current.
2. In electrolysis, the circuit must contain with:
a) electrode
b) Aqueous solution
c) Electric current
d) Wires
3. Log on the web side and observe the animation to answer the question.
http://www.tutorvista.com/content/chemistry/chemistry-ii/electrolysis/electrolysis-animation.php
http://www.tutorvista.com/content/chemistry/chemistry-ii/electrolysis/electrolysis-animation.phphttp://www.tutorvista.com/content/chemistry/chemistry-ii/electrolysis/electrolysis-animation.phphttp://www.tutorvista.com/content/chemistry/chemistry-ii/electrolysis/electrolysis-animation.php -
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Electrolysis is the dissociation of an electrolyte into ions at the electrodes by the passage of electric
current.
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This diagram show that when we use electrode and have electric current, the ions move. We used copper
electrode and copper sulfate solution.
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Question
1. What is the meaning of conductor?2. What do you understand about electrochemical series?3. Give three factor that affect electrolysis.
Answer
1. A conductor is a substance which conducts electricity but is not chemically changedduring the conduction.
2.
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ENHANCE
Application Of Electrolysis In Daily Life
The storage battery
A fully charged lead storage cell
A widely used lead acid battery, the storage battery was invented in 1859 by the French physicist
Gaston Plant. Reversing the chemical reaction can recharge this battery. It consists of three or six
cells, which are connected in a series. So the electricity generated by it is very strong.
Because of this, it has found wide usage in automobiles, trucks and other vehicles. The catch here
is that this type of battery runs down very quickly. However its ability to recharge itself while ini h d h h dl d i h i f i id d
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[14]
The table below shows three electrolytic cells with different electrolytes and different electrodes. You are required to answer each section by
writing your answer in the spaces provided.
1. In the diagrams, label the cathode with thesymbol and theanode with the symbol +.
2. Show the direction of the flow of theelectrons with arrowheads, >
3. Write the formula of all ions in theelectrolyte.
4. Write the formula of ions which areattracted to the cathode.
Underline the formula of ion which isselectively discharged.
5. Write the half equation to represent thereaction at the cathode.
6. What will you observe at the cathode?
7. Write the formula of ions which areattracted to the anode.
Underline the formula of ion which is
selectively discharged.8. Write the half equation to represent the
reaction at the anode.
9. What will you observe at the anode?
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[15]
Anwers :
1
2
3Na+, Cl
, H+ , OH
Na
+, Cl, H+ , OH
Cu
2+, SO42, H+, OH
4Na+, H+ Na+, H+ Cu2+, H+
52H
++ 2e H2 2H
++ 2e H2 Cu
++ 2e Cu
6 Gas bubbles are formed Gas bubbles are formedBrown solid deposited on the cathode
7Cl
, OH
ions Cl
, OH
ions SO4
2, OH
8
2Cl
Cl2 + 2e 4OH
2H2O + O2 + 4e Cu Cu2+
+ 2e
9Gas bubbles are formed Gas bubbles are formed Copper plate becomes thinner