seminar april revision form 5== chapter electrchemistry, carbon compound and thermo chemistry
TRANSCRIPT
Seminar chemistry form 5 ( Revision for topics)i) Electrochemistry
ii) Carbon compoundiii) Thermo chemistryDate : 5 April 2011
( Tuesday)
1)
Refer to the diagram above:Cell P
Electrode M
Electrode N
Name of cell
Label anode and cathode
State products
Electrolytic cell
Anode(positive electrode)
Cathode
(negative
electrode)
oxygen gas Copper metal
Stateobservations
Write ionic equations
Bubble of colourless gas that ignites the glowing wooden splinter
4OH- O2 + 2H2O + 4e
Brown solid is formed
Cu2+ +2e Cu
Cell P
State change of energy
Electrical energy Chemical energy
Refer to the diagram above:Cell Q
Electrode R Electrode S
Name of cell
Label anode and cathode
State products
Voltaic cell ( Daniel cell)
Anode(NEGATIVE ELECTRODE)
Cathode
( POSITIVE ELECTRODE)
Zinc ion Copper metal
State observations
Write ionic equations
Zinc Electrode becomes thinner
Copper electrode becomes thicker
Zn Zn2+ + 2e
Cu2+ + 2e Cu
Cell Q
State change of energy Chemical energy
Electrical energy
2)
Electrode P Electrode Q
a)State all ions present
b)Label anode and cathode
Answer the following questions
K+, H+, Cl-, OH-
Cathode Anode
b)Label anode and cathode
c)State ions attracted to
d)State ions discharged
e)State products and what is the factor involved?
H+ Cl-
Hydrogen gas
Chlorine gas
K+ ,H+ Cl-,OH-
Cathode Anode
e)State products and what is the factor involved?
Factor involved
Hydrogen gas
Chlorine gas
Position of ions in ECS
Concentrations of ions in solution
f)Give a reason why you have the product as mentioned above?
Position of hydrogen ion is lower than potassium ion in Electrochemical Series
Chloride ion is more concentrated than hydroxide ion
g)Write ionic equations
2H+ + 2e H2
2Cl- Cl2 + 2e
h)State observations and how do you test the products?
-Bubble of colourless gas is released.- Bring a lighted wooden splinter to the mouth of test tube, a ‘pop’ sound is produced
-Bubble of yellowish gas is released. -Bring a piece of moist blue litmus paper to the mouth of the test tube.-Blue litmus paper turns red then bleached
i)If the experiment is repeated with concentration of solution 0.001 mol dm-3. State the products . And what is the factor involved?
Hydrogen gas.Position of ion in Electrochemical series
Oxygen gas.
Position of ion in Electro
chemical series
3) Organic reaction
Ethene
ethanol
Ethyl ethanoate
CO2 + H2O
Ethanoic acid
Reaction 2Reaction 1
Reaction 4
Reaction 3 Reaction 5Reaction
6
A)Refer to the above reaction:
Reaction 1
a)Name of reactions
b)Reagents used
Combustion
Excess oxygen
Reaction 1
c)Conditions (if any)
d)Equations
Heat in excess oxygen
C2H5OH + 3O2
2CO2 +
3H2O
A)Refer to the above reaction:
Reactions 2
a)Name of reactions
b)Reagents used
Dehydration
Porcelain chip (Al2O3)
Reaction 2
c)Conditions (if any)
d)Equations
Pass ethanol over heated porcelain chips
C2H5OH
C2H4 + H2O
A)Refer to the above reaction:
Reactions 3
a)Name of reactions
b)Reagents used
Hydration
Steam
Reaction 3
c)Conditions (if any)
d)Equations
-Catalyst,H3PO4
-Temperature,300oC-Pressure, 60atm
C2H4 + H2O C2H5OH
A)Refer to the above reaction:
Reactions 4
a)Name of reactions
b)Reagents used
Esterification
Glacial Ethanoic acid and
concentrated sulphuric acid as the
catalyst
Reaction 4
c)Conditions (if any)
d)Equations
warm the mixture
C2H5OH+ CH3COOH
CH3COOC2H5 + H2O
A)Refer to the above reaction:
Reactions 5
a)Name of reactions
b)Reagents used
Esterification
Absolute Ethanol and concentrated sulphuric acid as
the catalyst
Reaction 5
c)Conditions (if any)
d)Equations
warm the mixture
C2H5OH+ CH3COOH
CH3COOC2H5 + H2O
A)Refer to the above reaction:
Reactions 6
a)Name of reactions
b)Reagents used
oxidation
Acidified K2Cr2O7 or acidified KMnO4
Reaction 6c)Conditions (if any)d)Equations
warm the mixture
C2H5OH+ 2[O]
CH3COOH + H2O
B)Draw diagram for experiment to carry out for reaction 2
Describe the coagulation of latex when exposed to air
5) A student obtained the data to determine heat of precipitation of PbSO4Solution Vol
(cm3)Conc(moldm-3)
Initial temp(0C)
Pb(NO3)2 50 0.5 27.4
Na2SO4 50 0.5 27.6
Highest temperature : 30.5 0C
What is meant by heat of precipitation?
• Heat changed when 1 mole of precipitate is formed from its ions in an aqueous solution
b) Calculate heat of precipitation of PbSO4
• Mole Pb 2+ : (0.5)(50)/1000 = 0.025 mol• Mole SO4 2- : (0.5)(50)/1000 = 0.025
mol• Pb2+ + SO2-
4 PbSO4
mole PbSO4 = Mole Pb2+ or mole SO2-4
= 0.025 mol
ϴ = 30.5 - ( 27.4 + 27.6 ) 2 = 3.0 ° CHeat of precipitation = mCϴ mol = ( 100)(4.2)(3) 0.025 = 50400 J/mol ∆ H = - 50.4 KJ/mol
d)Write thermo chemical equation
• Pb2+ + SO42- PbSO4
∆ H = - 50.4 KJ/mol
e) Write the ionic equation
• Pb2+ + SO42- PbSO4
E) Construct energy level diagram
Pb2+ + SO42-
Energy
∆ H = - 50.4 KJ/mol
PbSO4
f) The experiment is repeated using K2SO4 to replaced Na2SO4. Heat of precipitation
of PbSO4 remain the same. Explain.
• Because the same precipitate is formed, which is PbSO4.
• Only Pb 2+ ions and SO4 2- ions react
• Na+ ions and K+ ions do not react
• 6) A student carried out an experiment to determine heat of displacement of copper from CuSO4 solution. He added excess zinc powder to 50 cm3 of 0.2 moldm-3 CuSO4. The thermo chemical equation is shown below :
Zn + Cu2+ Zn2+ + Cu ∆ H = -80.64 KJ/mol
a) Calculate the change in temperature
Mol Copper= mol copper(II) sulphate = (0.2)(50)/1000 = 0.01 mol
∆ H = mCϴ mol80 640 J = ( 50)(4.2)(ϴ) 0.01 ϴ = 3.8 ° C
b) Write the ionic equation
Zn + CuSO4 Cu + ZnSO4
Zn + Cu2+ Zn2+ + Cu
The experiment is repeated with the following changes. What is the effect in the change of temperature when :• Concentration of CuSO4 is doubled,
without changing the volume :
So, change of temp or ϴ is doubled. Because as the concentration doubled, the number of particle per unit volume also doubled.
The experiment is repeated with the following changes. What is the effect in the change of temperature when :
• volume of CuSO4 is halved, without changing the concentration :
So, change of temp or ϴ is remain the same. Because, the changes in volume do not affect the number of particles per unit volume
7) State the diff betw heat change and the heat of reaction
HEAT CHANGE HEAT OF REACTION
A) OTHER NAMES
Depends on name of reactions :
Heat absorb, heat
released
-Heat of Precipitation-Heat of displacement-Heat of neutralisation-Heat of combustion
7) State the differences between heat change and heat of reaction
HEAT CHANGE HEAT OF REACTION
B) FORMULA USED H= mCϴ ∆ H= mCϴ
molC)UNIT Joule Kilo Joule/ molD) SYMBOL none ∆ HE) SIGN No sign Either + for
endothermic rex or – for exothermic rex