seminar april revision form 5== chapter electrchemistry, carbon compound and thermo chemistry

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