Physical Sciences Gr12 2012

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MTNLearnPhysical SciencesGrade 12

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GRADE12PHYSICALSCIENCES

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CONTENTS

Introduction

Broadcast Schedules

Preparing for Examinations

Exam Techniques

Exam Overview

Prelim Preparation

Spring School

Prelim Review

Exam Revision: Paper 1 (Physics)

Exam Revision: Paper 2 (Chemistry)

Listeners Feedback Competition

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INTRODUCTION

Have you heard about Mindset? Mindset Network, a South African non-profit organisation,was founded in 2002. Through ourMindset Learn programme, we develop and distribute

high quality curriculum aligned educational resources for Grade 10 - 12. We make thesematerials available on TV (Dstv and Toptv channels 319), the Internet(www.mindset.co.za/learn) and as DVDs and books.

At Mindset we are committed to helping South African learners succeed. This is why MindsetLearn is proud to offerMindset Learn Xtra especially for Grade 10 12 learners. Learn Xtraoffers you hundreds of hours of video and print support, live television shows between 4pmand 7pm every Monday to Thursday and a free Helpdesk where our expert teachers are onstandby to help you. You can find out more about Mindset Learn Xtra atwww.learnxtra.co.za.

Learn Xtra also offers specific exam revision support. Every year we run Winter, Spring,Exam and Supplementary Schools to help you ace your exams. And now, Mindset is proudto announce a powerful partnership with MTN and the Department of Basic Education tobring you Mindset Learn Xtra Radio Revision powered by MTN a full 3 months of radioprogrammes dedicated to supporting Grade 10 and 12 Mathematics, Physical Sciences andEnglish First Additional Language.

Participating Community Radio Stations

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Getting the most from Mindset Learn Xtra Radio Revision

The Grade 12 Physical Sciences we will focus on questions that come from recent previousexam papers. Please ask you teachers for copies of the exam papers or download thequestion papers and memos from our website or www.education.gov.za This booklet

contains diagrams taken from the exam papers so that you will be able to follow what is saidduring the broadcast.

Before you listen to the show, read through the questions for the show and try to answerthem without looking up the solutions. If you have a problem and cant answer the q uestion,dont panic. Make a note of any questions you have. When listening to the show, compareyour approach to the teachers. Dont just copy the answers down but take note of themethod used.

Make sure you keep this booklet. You can re-do the questions you did not get totally correctand mark your own work.

Remember that exam preparation also requires motivation and discipline, so try to staypositive, even when the work appears to be difficult. Every little bit of studying, revision andexam practice will pay off. You might benefit from working with a friend or a small studygroup as long as everyone is as committed as you are. Mindset believes that Mindset LearnXtra Radio Revision will help you achieve the results you want.

If you find Mindset Learn Xtra Radio Revision a useful way to revise and prepare for yourexams, remember that we will be running the following other great Learn Xtra Exam Revisionprogrammes on Dstv and Toptv channels 319 during rest of 2012:

Grade 12 Mindset Learn Xtra Spring School: 1st October to 5th October

Grade 11 and 12 Mindset Learn Xtra Exam School: 22nd October 20th November

Both Spring School and Exam School will cover Mathematics, Physical Sciences, Life

Sciences, Mathematical Literacy, English 1st Additional Language, Accounting and

Geography.

Contact us

We want to hear from you. So let us have your specific questions or just tell us what youthink through any of the following:

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www.learnxtra.co.zaMindset

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BROADCAST SCHEDULE

PRELIM PREPARATION

Date Time Topic27-Aug 18:00 -19:00 Vertical Projectile Motion28-Aug 18:00 -19:00 Momentum & Doppler Effect29-Aug 18:00 -19:00 Work Energy Power30-Aug 18:00 -19:00 Electrostatics, Capacitors & Electric Circuits02-Sep 17:00 -18:00 Electrodynamics & Electromagnetic Radiation03-Sep 18:00 -19:00 Organic Molecules04-Sep 18:00 -19:00 Organic Reactions05-Sep 18:00 -19:00 Rates of Chemical Reactions06-Sep 18:00 -19:00 Chemical Equilibrium09-Sep 17:00 -18:00 Electrochemistry & Chemical Industries

SPRING SCHOOL

Date Time Topic01-Oct 10:00 -11:00 Mechanics02-Oct 10:00 -11:00 Organic Chemistry03-Oct 10:00 -11:00 Electricity04-Oct 10:00 -11:00 Rates & Chemical Equilibrium05-Oct 10:00 -11:00 Waves, Light & Sound07-Oct 17:00 -18:00 Electrochemistry

PRELIM REVIEW

Date Time Topic08-Oct 18:00 -19:00 Mechanics09-Oct 18:00 -19:00 Organic Chemistry10-Oct 18:00 -19:00 Electricity11-Oct 18:00 -19:00 Rates & Chemical Equilibrium14-Oct 17:00 -18:00 Chemical Industries

EXAM SCHOOL

Date Time Topic23-Oct 17:00 -18:00 Motion, and Doppler Effect23-Oct 18:00 -19:00 Momentum and Work Energy & Power24-Oct 17:00 -18:00 Electricity24-Oct 18:00 -19:00 Electromagnetism26-Oct 17:00 -18:00 Organic Molecules & Properties26-Oct 18:00 -19:00 Organic Reactions28-Oct 17:00 -18:00 Rates & Chemical Equilibrium28-Oct 18:00 -19:00 Electrochemistry & Chemical Industries


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PREPARING FOR EXAMINATIONS

1. Prepare well in advance for all your papers and subjects. You need to start yourplanning for success in the final examination now. You cannot guaranteesuccess if you only study the night before an exam.

2. Write down the date of your prelim and final exam so that you can plan andstructure a study time table for all your subjects.

3. Set up a study time-table according to your prelim and final Grade 12 exam time-table and stick to your study schedule. If you study a small section every day,you will feel you have achieved something and you will not be as nervous by thetime you have to go and write your first paper.

4. Your study programme should be realistic. You need to spend no more than 2hours per day on one topic. Do not try to fit too much into one session. When youcover small sections of work often, you will master them more quickly. The

broadcast schedule may help you to make sure you have covered all the topicsthat are in the exam.

5. When studying dont just read through your notes or textbook. You need to beactive by making summary checklists or mind maps. Highlight the important factsthat you need to memorise. You may need to write out statements such asdefinitions and laws a few times to make sure you can remember these. Checkyourself as often as you can. You may find it useful to say the definitions andlaws out aloud.

6. Practise questions from previous examination papers. Follow these steps for

using previous exam papers effectively: Take careful note of all instructions - these do not usually change. Try to answer the questions without looking at your notes or the solutions. Time yourself. You need to make sure that you complete a question in

time. To work out the time you have, multiply the marks for a question bytotal time and then divide by the total number of marks. In most examsyou need to work at a rate of about 1 mark per minute.

Check your working against the memo. If you dont understand the answergiven, contact the Learn Xtra Help desk (email: [email protected])

If you did not get the question right, try it again after a few days.

7. Preparing for and writing examinations is stressful. You need to try and stayhealthy by making sure you maintain a healthy lifestyle. Here are someguidelines to follow:

Eat regular small meals including breakfast. Include fruit, fresh vegetables,salad and protein in your diet.

Drink lots of water while studying to prevent dehydration. Plan to exercise regularly. Do not sit for more than two hours without

stretching or talking a short walk. Make sure you develop good sleeping habits. Do not try to work through

the night before an exam. Plan to get at least 6 hours sleep every night.


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EXAM TECHNIQUES1. Make sure you have the correct equipment required for each subject. You need

to have at least one spare pen and pencil. It is also a good idea to put newbatteries in your calculator before you start your prelims or have a spare battery

in your stationery bag.2. Make sure you get to the exam venue early - dont be late.

3. While waiting to go into the exam venue, dont try to cram or do last minuterevision. Try not to discuss the exam with your friends. This may just make youmore nervous or confused.

4. Here are some tips as to what to do when you receive your question papers:

Dont panic, because you have prepared well.

You are always given reading time before you start writing. Use this time

to take note of the instructions and to plan how you will answer thequestions. You can answer questions in any order. Time management is crucial. You have to make sure that you answer all

questions. Make notes on your question paper to plan the order foranswering questions and the time you have allocated to each one.

It is a good idea always to underline the key words of a question to makesure you answer it correctly.

When you start answering your paper, it is important to read everyquestion twice to make sure you understand what to do. Many marks arelost because learners misunderstand questions and then answer

incorrectly. Look at the mark allocation. Make sure you do not give more detail than

required. When you start writing make sure you number your answers exactly as

they are in the questions. Think carefully before you start writing. It is better to write an answer

once and do it correctly than to waste time rewriting answers. DO NOT use correction fluid (Tippex) because you may forget to write in

the correct answer while you are waiting for the fluid to dry. Ratherscratch out a wrong answer lightly with pencil or pen and rewrite the

correct answer. Check your work. There is usually enough time to finish exam papers

and it helps to look over your answers. You might just pick up acalculation, language or a spelling error. In Physical Sciences make surethat every answer has the correct units. For vector quantities (force,displacement, velocity, acceleration, momentum, impulse and electricfield strength) make sure you include the direction as well.


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EXAM OVERVIEW

STRUCTURE OF PHYSICAL SCIENCES EXAM PAPERS

Section A (All topics)

One word answers 5 marksMultiple choice questions 20 marks

Section B (Long questions) 125 marks

PHYSICAL SCIENCE PAPER 1: PHYSICS TOTAL MARKS: 150 3 HOURS

Mechanics 50 marks Momentum in 1 D Grade 11 Impulse and change in momentum Vertical projectile motion Frames of reference Work, power and energy

Waves, Sound and Light 25 marks

Doppler effect 2D and 3D wave fronts

Electricity and Magnetism 55 marks Electrostatics Grade 11 Electric circuits Grade 11 Electrodynamics Grade 12 Electromagnetic radiation Grade 12

Matter and Materials 20 mark Optical phenomena and properties of materials

PHYSICAL SCIENCE PAPER 2: TOTAL MARKS: 150 3 HOURS

Matter and Materials 50 marks Organic molecules

Chemical Change 75 marks Energy and chemical change Grade 11 Rate and extent of reactions Electrochemical reactions

Chemical Systems 25 marks Chlor-alkali industry

Fertiliser industry Batteries


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prelim preparation

sTUDY NOTES


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PRELIM PREPARATION

ON AIR COMPETITION QUESTION FOR WEEK 1 (26 AUG 2 SEPT)

QuestionBall 1 is projected upwards with an initial velocity ofym.s-1. At the same time, ball 2 isprojected upwards with double the velocity of ball 1. Ignore the effect of air resistance. Ball1 reaches its maximum height aftert seconds. How long after this will ball 2 reach itsmaximum height?

A 0 s

B t s

C 2t s

ON AIR COMPETITION QUESTION FOR WEEK 2 (26 AUG 2 SEPT)

Question

Nitric oxide (NO(g)) forms in internal combustion engines by the direct combination ofnitrogen and oxygen according to the following reversible reaction:

N2(g) + O2(g) 2 NO(g)

During an experiment, 1 mol of O2(g) and 1 mol of N2(g) were place in a 2 dm3 closed

container at 300 K. After some time, chemical equilibrium was established and 0,2 mol ofNO was found in the container. What is the value for the equilibrium constant (Kc) for thereaction at this temperature?

A 0,20

B 0,06

C 0,05


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27-AUG 18:00 -19:00 VERTICAL PROJECTILE MOTION

STUDY NOTES

VERTICAL PROJECTILE MOTION

1. What is Projectile Motion?

A projectile is an object that is given an initial velocity by shooting or throwing etc.,and once launched, the only force acting on it is the force due to gravity. In theabsence of air resistance, the object is free falling with a constant (uniform)acceleration of 9,8 m.s-2 called gravitational acceleration (g). The direction of thisacceleration is always downwards.

2. Important Facts Concerning Vertical Projectile Motion:

At the greatest height of the upward motion:

vf= 0 ms-1a = g = 10 ms-2 downwards

The object will take the same time to reach its greatest height from point ofupwards launch as the time taken to fall back to point of launch

If the object is being released from rest or being dropped, its initial velocity is 0ms-1.

If the object is being thrown upwards, it must start with a maximum velocityand as it moves up, the velocity decreases until it stops.

When an object is thrown upwards, you can treat the motion as two parts(upwards and downwards) or as a single motion, but the acceleration must beconstant throughout the time. The sign of the direction of motion must stay thesame as well.

3. The Effect of Air Resistance

In most exam questions you will be told to ignore the effects of air resistance. Air resistance is a frictional force that opposes motion. When an object is moving up, air resistance will act downwards. When an object is moving downwards, air resistance will act upwards. Terminal velocity is reached when the downward force of gravity and the

upward force of air resistance are equal.

At terminal velocity there is no net force acting in on the object and so theacceleration is zero and the object falls at a constant velocity.


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4. Solving Vertical Projectile Motion Problems

To solve vertical projectile motion problem we use equations of motion and graphs ofmotion

Equations of Motion:

These are found on the information sheet and are used to describe and calculatethe motion of an object that is moving in one direction with a constantacceleration.

Method for Using Equations of Motion:

STEP 1: Draw a diagram of the situation in the question and enter all the numericalvalues onto your diagram.

STEP 2: Select a direction as positive and do not change the sign of the directionSTEP 3: Identify which equation to use, i.e. identify the known and unknown

quantitiesSTEP 4: Substitute into the equation and solve

STEP 5: Interpret the answer - for vector quantities, give the direction in words

Graphs of Motion

We use three different graphs.A. position time graph.B. velocity time graphC. acceleration time graph

Interpreting Graphs of Motion

Check the labels and units on the horizontal and vertical axes When the graph is above the horizontal axis, the position, velocity or

acceleration is positive. Identify the direction of motion from the graph.

The gradient of a position-time graph tells you about the velocity of the objectand the gradient of a velocity-time graph tells you about the acceleration of theobject.

The area between the graph and the time axis on a velocity-time graph givesthe change in position, and on an acceleration-time graph this area is thevelocity.

Use a ruler to read off values - start on the time axis and graph a vertical linetill it touches the graph; then graph a horizontal line and read off the value on

the vertical axis. Make sure you know what all three graphs of motion look like for the following

situations:

an object dropped from a height above the ground an object that is thrown up from the ground and falls back down again a ball that is dropped from a height and bounces up off the ground


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Sketching Graphs of Motion

Select the position of the observer (usually represented as the origin) Make sure you label the axes with units Select a good scale for an accurate graph Learn the basic shape of each of the graphs for the following situations:

stationary object constant velocity moving towards and away constant acceleration moving towards and away

Make sure you know when the velocity is zero Make sure you know when the velocity is increasing or decreasing Plot your points accurately After drawing the sketch check that the sketch describes the situation given

QUESTIONS FOR DISCUSSIONNov 2011 P1 Question 2.3 and 3

Diagram for Question 2.3 (Nov 2011 P1)

Diagram for Question 3 (Nov 2011 P1)


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28-AUG 18:00 -19:00 MOMENTUM & DOPPLER EFFECT

STUDY NOTES

MOMENTUMDefinition: Momentum is a vector quantity and has the unit: kgms-1.

p = mv

The Principle of Conservation of Linear Momentum

The total linear momentum of an isolated system remains constant in magnitude anddirection.

Impulse

Definition: Impulse is the change in momentum of a body ( p =m v =m(vfvi)

Impulse and Newtons 2nd Law

Newtons 2nd Law states that the net force exerted on an object is directly proportional to therate of change of momentum in the direction of the force net.

Equation: Fnet = m v t

Equation for Impulse: Fnet . t = m v

Units for Impulse: N.s

CollisionsThere are a number of different possible collisions that can take place between two objectsmoving along the same line (one dimension):

one moving object collides with a stationary object two objects move towards each other two objects pushed together and kept stationary. When they are released they move

apart (explosion)

Possible results

one object moves and the other object stops moving the two objects join together and move off at the same speed both objects move but are not joined

We classify collisions as either elastic or inelastic.

In an elastic collision kinetic energy and momentum are conserved. In an inelastic collision, momentum is conserved, but not kinetic energy.

The conservation of kinetic energy is determined by calculating the total kinetic energy of allparts of the closed system before the collision and comparing that to the total kinetic energyof all the parts of the closed system after the collision.


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DOPPLER EFFECT

Definition:The Doppler Effect occurs when the frequency of waves produced by a sourceis observed to be higher or lower than the actual frequency of the source.

The Doppler Effect can be observer using water waves, sound waves or light.

Facts about The Doppler Effect you must learn

There must be relative motion between the source of waves and the observer. For Grade 12 examinations, one object will be stationary The most common example of the Doppler Effect is for sound waves For sound waves:

Increasing the frequency means the pitch increases Decreasing the frequency means the pitch decreases

When the observer moves towards the source or the source moves towards theobserver, the frequency increases

When the observer moves away from the source or the source moves away from theobserver, the frequency decreases

The Doppler Effect Equation

L vvvv

fL = frequency of the listener fs = frequency of the sourcevL = speed of the listener vL = speed of the sourcev = speed of sound in the given medium

Although the equation looks complicated, it simply describes the relationship between thefrequency of the listener and frequency of the source.

The part in brackets is a ratio of the velocities and can either be:

a number bigger than 1 (source or listener are moving towards each other)

equal to one

a number smaller than 1 (source or listener are moving away from each other)


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Using the Doppler Effect Equation

1. Write down the formula with the signs.

2. There are two methods to decide on the sign:

Method A

Define the direction from the listener (L) towards the source (s) as positive (+).Substitute the values of the unknown velocities with this sign convention and thusreplace the sign in the equation.

Method B

If either the source or listener is moving towards the other, then the frequency of thelistener (fL) must be greater than the frequency of the source (fs).This means that in the ratio of velocities, the numerator must be bigger than thenumerator. Select the plus sign to increase the numerator and the minus sign to

decrease the denominator so the equation becomes:

L vvvv

If either the source or listener is moving away from the other, then the frequency ofthe listener (fL) must be smaller than the frequency of the source (fs).This means that in the ratio of velocities, the numerator must be smaller than thenumerator. Select the minus sign to decrease the numerator and the plus sign toincrease the denominator so the equation becomes:

L vvvv

3. Substitute zero values for the velocity of the source or the observer into theequation.

4. Substitute the speed of sound given in the question or use:

Speed of sound in air= 340m.s-1

5. Solve for the unknown.


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QUESTIONS FOR DISCUSSION:

Nov 2011 P1 Question 2.1 and 4

Nov 2011 P1 Question 6

Diagram for Question 4.1 - 4.2 (Nov 2011)

Diagram for Question 4.3 - 4.4 (Nov 2011)


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29-AUG 18:00 -19:00 WORK ENERGY POWERSTUDY NOTES

WORK

Definition: Work done is energy transferred and it is measured in the unit of Joules. Work is

not a vector but a scalar quantity.

We dont indicate direction for work.

Equation for Calculating Work

W = Fxcos

When the force and change in position are in the same direction, the angle betweenthese vectors is 00. Since cos = 1, the work done is a maximum.

When the force and change in position are in the opposite direction, the anglebetween these vectors is 1800. This gives a negative answer for the work done as theforce will be a frictional force.

When the force and change in position are at 900 to each other (perpendicular), nowork is done (cos900 = 0).

ENERGY

Energy is also a scalar quantity. Energy is the ability to do work and is also measured inJoules

Kinetic energy is the energy as a result of movement

K = Ek = mv2

Gravitational Potential Energy is the energy possessed as a result of position

U =Ep = mgh

Mechanical Energy is a combination of kinetic and potential energies.

Mechanical Energy = Potential Energy + Kinetic Energy

Emech = U + K = Ep + Ek

Law of Conservation of Energy

Energy cannot be created nor destroyed. Energy can only be converted from one form to

another.

During free fall, mechanical energy is conserved

Emech (initial) = Emech (final)

Friction is a non-conservative force and where friction is present, mechanical energy is not

conserved. The energy lost is due to the work done by the frictional force and may be

converted into heat, sound, electrical energy or even light.


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WORK- ENERGY THEOREM

The work done by a constant net force in displacing an object is equal to the change in

kinetic energy of the object.

Wnet = Ek = Fx.cos

POWER

Power is also a scalar quantity. It is measured in the unit of Watts.

Power = work done time

= energy transferred time

When a machine causes an object to move at constant velocity we can calculate the power

of the machine by using the equation:

P = F.v

QUESTIONS FOR DISCUSSION

Nov 2011 P1 Question 2.2 and 5




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30-AUG 18:00-19:00 ELECTROSTATICS, CAPACITORS &ELECTRIC CIRCUITS

STUDY NOTES

ELECTROSTATICS

You must revise the following topics from Grade 11:

Electric Fields

An electric field is a region in space in which an electric charge will experience aforce represented by a pattern of field lines.

Check that you can draw and interpret the electric field pattern for different pointcharges and between parallel plates.

Conservation of Charge

The Law of Conservation of Charge states that charges cannot be created nordestroyed but are merely transferred from one object to another, i.e. the amount ofcharges in a closed system remains the same.

Use the equation below to calculate the charge on two spheres that are brought into contactand then separated:

Qnew = (QA+QB) 2

Coulombs Law of Electrostatics

The Coulombs Law states that the force of attraction or repulsion between the twoelectric charges at rest is directly proportional to the product of the charges, andinversely proportional to the square of the distance between them.

F = KQ1Q2r2

Q = charge, unit: coulomb (C) r = distance between the charges, measured in m

k = Coulombs constant = 9 x 109 Nm2C-2

Electric Field Strength

Electric field strength is the force per unit charge which a positive charge willexperience at that point

Equation when using a point charge:

E = Fq

Units: Force Newton (N), Charge coulomb (C), Field Strength N.C-1


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Electric Field Strength around a large charged sphere (Q)

The electric field strength at a distance from charge Qis given by the equation.

E = kQ

r2

Electrical Potential Difference

A charge placed at any point in an electric field possesses potential energy.

Thepotential energyin an electric field is defined as the work it takes to move a unitpositive charge from the point at lower potential to the point at higher potential.

V = WQ

Units: V volts (v), W joule (J)

Electric Field Strength between two charged parallel plates

The electric field strength between 2 oppositely charged parallel plates is uniform,i.e. a charge placed anywhere between these plates will have a constant force actingon it.

The electric field strength between the plates is calculated using the equationE = Vd where d is the distance between the plates in m, and V is the potentialdifference measured in volts

CAPACITORS

Acapacitoris a device that can store energy.

Inside a capacitor the terminals connect to two metal plates that are separated by aninsulating material called a dielectric. The dielectric can be anything that does notconduct electricity readily and it keeps the plates from touching each other.

The bigger the area of the plates, the more charge the capacitor can store.

Symbol:

Four factors affect the ability of the capacitor to store electrical charge. These are o The potential difference between the plateso The area of the plateso The distance between the plateso The insulating substance between the parallel plates.


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Capacitance

Capacitance is a measure of the ability of a capacitor to store charge.

The capacitance (C) of a capacitor is the charge stored on its plates per volt ofpotential difference between the plates.C = QV

The units for capacitance is coulomb per volt (C.V-1) called a farad (F).

The farad is a very large unit. Typical capacitor are ino Microfarads, F = 10-6Fo Nanofarads, nF = 10-9Fo Picofarads, pF = 10-12F

ELECTRIC CIRCUITS

Resistance and Ohms Law

Ohms Law states thatthe current between any two points in a conductor is directlyproportional to the potential difference between these points provided that thetemperature of the conductor remains constant.

Equation: R = VI

Units : current amperes (A), voltage volts (V) and resistance ohms ()

The resistance of the conductor depends on

o The type of material usedo The length of the conductor the longer the conductor, the greater the resistanceo The thickness of the conductor the thicker the conductor, the smaller the

resistanceo The temperature of the conductor the higher the temperature, the greater the

resistance


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Series and Parallel Connections

Components Connection Diagram Current(A)

Potential Difference(V)

Resistors Series

RT = R1 + R2

The current in agiven seriescircuit is thesamethroughout thecircuit.

The moreresistors inseries, the

greater theresistance; thecurrentdecreases.

Resistors in series

are potential

dividers, i.e.

VT = V1 + V2

Resistors Parallel

1 = 1 +

1

RT R1

R2

Resistors in

parallel in a given

circuit split the

current.

AT = A1 + A2

(the moreresistors inparallel, thegreater the totalcurrent becausethe totalresistance

decreases.)

Resistors in

parallel have the

same potential

(in the absence

of anotherresistor in

series).

VT = V1 = V2

AT

VT

R1

R2

V2

V1

A1

A2

A

VT

R1R2

V1 V2


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EMF and Internal Resistance

The emfof a cell is the maximum amount of energy which the cell can supply.

We measure the emf of a cell or battery by connecting a voltmeter across theterminals. The battery may be connected to an open circuit

When the cell is delivering current to a circuit (closed circuit), the terminal potential

difference is less than the emf; the difference is called lost volts or internal volts. The reason there is a difference between the emf and potential difference across the

terminals of a battery in a closed circuit, is that there is an internal resistance insideeach cell.

Equation

emf = terminal potential difference + lost volts

Emf = IR + Ir

Emf = I(R + r)

Energy in an Electric Circuit

Potential difference in an electric field

Potential differenceV = W Q

Quantity of charge:

Q = I t

Work done by an electric field:W = V I t

Power: the rate at which work is done

Power = workTime

Units: watt (W)

Electrical Power:P = V I or P = I2R or P= V2 R


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Nov 2011 P1 Question 8, 9 and 10

Diagrams for Question 8 (Nov 2011 P1)



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02-SEP 17:00 -18:00 ELECTRODYNAMICS &ELECTROMAGNETIC RADIATION

STUDY NOTES

ELECTRODYNAMICS

There are two electrical machines that you need to know about:

The Electric Motor (Supply electrical energy produce mechanical energy)

The Electric Generator (Supply mechanical energy produce electrical energy)

The Electric Motor

In an electric motor, an electric current passes through a coil in a magnetic field. The

combination of the two force fields produces a torque (rotation) which turns the coil of themotor.

The split ring commutator reverses the current each half turn to keep the coil turning in the

same direction. The brushes on the commutator allow for the free rotation of the coil.

If we want to maximise the force created by the motor effect we can:

Make the current stronger

Increase the strength of the magnetic field

Make sure that the angle between the magnetic field direction and the direction of the

current is as close to 90 as possible, since the maximum effect is when the currentflows at 90

to the magnetic field lines.

The Electric Generator (Dynamo)

The generator illustrates the principle of electromagnetic induction.

Faradays Law of Induction

The induced emf in a conductor is directly proportional to the rate of change of themagnetic flux through the conductor.

There are two types of generators:

A DC generator: Same structure as a motor but the coil is turned and produces Direct

Current (D>C). This machine has a split ring commutator.

An AC Generator (Dynamo): This machine has slip rings and produces alternating current


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Alternating Current

Our power stations produce alternating current and the current that we get from the plugpoints in our homes is AC. The frequency of alternating current in South Africa is 50Hz. Thegraph below shows how the current changes direction every half revolution, and is changingstrength continually as the coil rotates in the magnetic field.

Advantages of AC

We can use transformers to step up the voltage and step down the current. This enables thedistribution of electricity on the national power grid with low energy loss.

Calculations for AC

The potential difference varies between 0V and 311V. This has the same effect as a

constant value of 220V. We call this the root mean square voltage

The current also fluctuates with time:

The average power in an AC circuit is calculated by using:

Pave = VRMS IRMS

Pave = I2RMSR

Pave = V2

RMS R


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ELECTROMAGNETIC WAVES

Source: http://www.warren-wilson.edu

Electromagnetic waves can be set up by charges that oscillate backwards and forwards. The

oscillation causes a vibration which in turn causes a wave shaped electric field. As the

electric field changes, it induces (creates) a changing magnetic field at right angles to it. As

the magnetic field changes, it induces a changing electric field at right angles to it. It this waythe wave self propagates (keeps on going).

The magnetic and electric fields are in phase with one another.

Electromagnetic waves are transverse waves.

Electromagnetic waves do not need a physical medium to travel in. They can travel through

a vacuum.

All electromagnetic waves travel at a speed c = 3 X 108 m.s-1 (in a vacuum)

v = c = f x

THE ELECTROMAGNETIC SPECTRUM

There are different types of electromagnetic waves which we arrange in order of increasing

frequency in spectrum:

Radio waves, Microwaves, Infra-red, Visible Light, Ultra-violet light, X-rays, Gamma Rays.


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PROPERTIES OF LIGHT

SPECTRA

There are three types of spectra you need to be able to explain:

Visible spectrumWhen visible white light is refracted through a prism, we see the colour of the

different frequencies of light (colours of the rainbow).

Line emission spectrum

When energy is given to any element in its gas phase, it will radiate light of certain

frequencies. When this light is refracted through a prism, a unique pattern of lines

appears for each element. These lines correspond to the energy levels of electrons in

the atoms that have been excited.

Line absorption spectra

A line absorption spectrum is formed when white light is passed through a

cold gas (element) and then passed through a prism. We see a continuous spectrum

but with a unique pattern of black lines. The black lines represent frequencies of light

that have been absorbed by the gas.

Diffraction of Light

When light of a single frequency passes through a small slit, a diffraction pattern will form asshown below:

Source: Wikipedia - Diffraction


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Equation for Calculating the Angle of Diffraction,

sina

m

= angle of diffraction (between the normal to the slit and the dark fringes).

d = width of slit (m).

= wavelength of light (m).

m = the number (+1, +2, +3 etc) of the dark band from the centre of the diffraction pattern.

Youngs Double Slit Experiment

When light of the same frequency (colour) passes through two narrow slits close to each

other, a pattern of evenly spaced bright and darker bands can be projected onto a screen.The bright bands are formed as a result of constructive interference, while the darker bands

are a result of destructive interference. This experiment confirms that light has wave

properties.

Interference: The Principle of Superposition

The magnitude of the resultant displacement is the algebraic sum of the displacements of the

pulses before interference occurs.

In other words: When two waves meet, they interact with one another.

When two peaks meet, they make a larger peak equal in amplitude to the size of thesum of the amplitudes of the original two waves. This is constructive interference oran anti-node.

When two troughs meet, they make a larger trough equal in amplitude to the size ofthe sum of the amplitudes of the original two waves. This is constructive interferenceor an anti-node.

When a peak and a trough meet, they make a smaller peak or trough equal inamplitude to the size of the difference between the amplitudes of the original twowaves. This is destructive interference or a node.

Photoelectric Effect

When light of high enough energy collides with an electron near the surface of a metal, ittransfers all its energy to the electron. If the electron gains enough energy, it is knocked offthe metal surface.

Wave theory relates the energy of the wave to amplitude (intensity / loudness). Increasingthe brightness of a red light does not knock off electrons from the surface of a metal but adim ultraviolet light does. Wave theory of light cannot explain this result.

Planck suggested that energy was quantised and depended on frequency. Einstein appliedPlancks ideas to light and proposed that light consists of particles called photons. The

energy of the photon (a packet of energy) is given by the equation:

E= hf h = Planks constant (6,6x10-34

Js)


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Different metal surfaces require different amounts of energy to release an electron. Theminimum amount of energy required is called the work function of the metal (W0) and thiscorresponds to the threshold frequency of the photon (f0). When the energy of the photon isgreater than the work function, the electrons knocked off the surface of the metal gain kineticenergy too. Hence the equation for the photoelectric effect is:

E = h.f= W0 + Ek = h.f0 + m v2

Increasing the brightness (intensity) of a source of light increases the number of photonsreleased and will increase the number of electrons knocked off if the photons have enoughenergy. The photoelectric effect gives evidence that the light has a particle nature.

Duality of Light

Light has both a wave nature and a particle nature at the same time.

De Broglies Wave Equation

Based on the duality of light, de Brogile suggested that all particles behave as waves do. Ithas been shown that very small particles, such as electrons and neutrons, form aninterference pattern similar to X-rays. For bigger particles like a tennis ball, the wavelengthsare very small and effectively meaningless.

de Broglies wavelength (m) hPlanks constant (6,6x10-34

Js)

m mass of particle (kg) v velocity of particle (ms-1)


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Nov 2011 P1 Question 11, 12, 7




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03-SEP 18:00 -19:00 ORGANIC MOLECULES

STUDY NOTES

ORGANIC MOLECULESImportant features of Carbon

Carbon has a valency of 4 (can form 4 bonds), and has 4 valence electrons (outermostenergy level).

Carbon has the ability to form long chains with other C atoms called catenation. Carbon has the ability to form rings by joining with other C atoms

Representations of Organic Molecules

Molecular formula: C6H13OH

Condensed formula:

Structural formula:

HYDROCARBONS

Theyaremolecules that contain only hydrogen and carbon atoms. There are an infinite

number of different hydrocarbon molecules.Functional group: The special arrangement of atoms in part of a molecule that gives the

molecule particular characteristics.

Types of hydrocarbons

Saturated single bonds only (functional group)

Unsaturated double and triple bonds (functional group)

Homologous Series

Family or group of molecules that have the same functional group and the same general

formula.

Alkanes

Single covalent bonds

SATURATED molecule. General formula: CnH2n+2

Alkenes

have one or more C=C double bonds The general formula: CnH2n. UNSATURATED molecule

CH3CH2CH2CH2CH2CH2OH

CH3 - CH2-CH2-CH3

butane

CH2=CH-CH2-CH3

but-1-ene


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Alkynes

One or more triple bonds

General formula: CnH2n-2

UNSATURATED molecule

Naming alkyl groups (side chains)

Alkyl group structure Alkyl name

CH3

- methyl

CH3CH

2- ethyl

CH3CH2CH2 - propyl

CH3CH

2CH

2CH

2- butyl

RULES FOR NAMING ORGANIC COMPOUNDS (IUPAC RULES)

Identify the functional group of the molecule this determines the ending of thename, e.g. all alkanes end in ane.

Find the longest continuous carbon chain and allocate its prefix according to the

number of carbon atoms in the chain (see table for prefixes).

NNaammee pprreeffiixxeess

No of C atoms Prefix

1 meth

2 eth -

3 prop -

4 but -

5 pent -

6 hex -

7 hept -

8 oct -

Number the carbon atoms in the chain. Number them so that the functional group is

on the carbon of lowest possible number. Double and triple bonds take preferenceover side chains.

Name the branched group according to the number of carbon atoms it has, and give ita number according to the carbon atom to which it is attached.

CHC-CH2-CH3

but-1-yne


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If there is more than one branched group of the same kind, use the Greek prefixes di,

tri, tetra, penta and so on to indicate this.

If a halogen atom is attached to the carbon chain, it is treated as an alkyl group andthen the prefixes: fluoro-, chloro-, bromo -, and iodo are used.

Alcohols

-O-H (hydroxyl) is the functional group. (Not called hydroxide OH-)

Named using the ending ol. O-H group gets the lowest possible number

Alcohols are oxidised to carboxylic acids when treated with strong oxidising agents

Alcohol molecules have a non-polar hydrocarbon end and a polarO-H section

Alcohols are solvents for polar and non-polar solutes Classification of alcohols depends on the number of carbons attached to the carbon

bonded to the hydroxyl: Primary only 1 carbon, Secondary ( 2 carbons) andTertiary ( 3 carbons)

Carbolic Acids Compounds that have the carboxyl, -COOH functional group

The ending -oic acid denotes that we are dealing with a carboxylic acid.

Are relatively weak acids.

Esters

These are compounds that have the C-O- C functional group. Esters arise by the reaction between a carboxylic acid and an alcohol: All esters consist of two parts in their name:

o First part: an alkyl derived from the alcohol used,o Second part (separate word) ends in -anoate derived from a carboxylic acid

(has the double bond O)

Ketones

Functional group: Carbonyl group (C=O) found in the middle of the molecule Suffix: -one ( pronounced own)

Example: propanone

The carbonyl group (C=O) is polar.

Aldehydes

Functional group: Carbonyl group (C=O) found at the end of the molecule Suffix: -al

Example: propanal

O

H


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ISOMERS

Isomers are compounds which have the same molecular formula, but different structuralformulae.

PHYSICAL PROPERTIES OF ORGANIC MOLECULES

Molecules are held together by intermolecular forces. In order to separate these moleculesfrom each other requires energy. The stronger the intermolecular forces, the more energythat is required to separate or break these bonds. This will lead to a higher melting point,boiling point, etc.

Boiling and Melting Points

As the strength of the intermolecular forces increase, the boiling point and melting point willincrease. Thus molecules where there are hydrogen bonds present will have a highermelting point and boiling point than those molecules where there are weaker London forcesor Van der Waals forces present.

Vapour Pressure

Vapour pressure is the amount of pressure that the gaseous molecules exert above thesurface of the liquid phase. The vapour pressure will decrease as the size of the moleculeincreases (chain length).Vapour pressure is an indication that there are weak intermolecular forces present in theliquid phase.

Viscosity

A liquid that has a low viscosity will be able to flow more easily. Thus, where hydrogen bondsare present, there will be a much higher degree of viscosity. The opposite is true for theweak Van der Waals forces. Viscosity will also increase as the length of the carbon chain

increases.

Density

The density of organic molecules will increase as the length of the chain increases.

Surface Area

As the surface area of the molecule decreases, there will be lower boiling and melting points

as the intermolecular forces will be weaker.

Phases

As the chain length increases, the melting and boiling points will increase. The smallermolecules will then be gases at room temperature and the longer chain lengths will be liquidsor solids at room temperature


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Nov 2011 P2 Question 3 & 4




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04-SEP 18:00 -19:00 ORGANIC REACTIONS

STUDY NOTES

ORGANIC REACTIONS

Combustion reactions:

Hydrocarbons react with oxygen to form water and carbon dioxide andenergy.

Alkane example:

Alkenes and Alkynes undergo similar reactions to form the same products.

Substitution reactions

An atom or group of atoms in a molecule is substituted by another.

One atom or group is removed and another takes its place.

E.g.1 CH4(g) + Br2(g) CH3Br(g) + HBr(g) Halogenation

E.g. 2 CH3Cl(g) + H2O(l) CH3OH(aq) + HCl(aq) Hydration

Addition reactions

Reverse of elimination reactions. The number of molecules decreases in addition reaction (on product side). High T favour elimination reactions and low T favour addition reactions. Therefore, we can drive reactions in opposite paths. Addition reactions generally occur faster than substitutions reactions.

E.g. C2H

4(g)+ H

2O(l) C2

H5OH(g)

Elimination reactions

Molecule of a reactant breaks up to form 2 or more new molecules

Opposite of addition reactions. Number of molecules greater on product side.

Single bond is ELIMINATED and double bond forms!E.g. 1 C2H5OH(g) + --(conc. acid + heat) C2H4(g) + H2O(l) + H

+

Dehydration is the elimination of the hydroxyl (-OH) and the H atom from the alcohol.

E.g. 2 C2H5Cl(aq) + NaOH(aq) C2H4(g) + NaCl(aq) + H2O(l)

Dehydrohalogenation is the elimination of the halogen atom (Cl) and an H atom leaving a

carbon = carbon bond strong base is used.


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Cracking

Heating to a high temperature Produces unsaturated products

E.g. CH3

CH3 CH

2= CH

2+ H

2

Oxidation

Alcohols for example can also undergo oxidation. Oxidation of a primary alcohol: K2Cr2O7 as catalyst forms and aldehyde. Oxidation of a secondary alcohol: K2Cr2O7 as catalyst forms a ketone.

QUESTIONS FOR DISCUSSIONNov 2011 P2 Question 5



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05-SEP 18:00 -19:00 RATES OF CHEMICAL REACTIONS

STUDY NOTES

ENERGY CHANGES DURING CHEMICAL REACTIONS Most reactions do not begin until an amount of energy (activation energy) has been

added to the reaction mixture.

The activation energyis often called the energy hillwhich must be overcome bythe addition of this amount of energy before a reaction can take place.

When activation energy is added to the reactants, a so-called activated complexisformed.

Activated complex temporary, unstable, high-energy composition of atoms, whichrepresents a transition state between reactants and the products.

When the activated complex is formed during a reaction, this complex can lead either

to the formation of new bonds, i.e. molecules of the products, or to re-formation of theold bonds, thereby returning to being reactants.

For the reaction

AB + C A + BC

The formation of an activated complex as a transitional step can be represented as

follows:

AB + C [ABC] A + BC

The peak of the energy hill indicates the energy of the activated complex.

When an activated complex is formed during a reaction, this complex can lead either

to the formation of new bonds, i.e. molecules of the products or to the re-formation ofthe old bonds, thereby returning to being the reactants. This is reversibility for thereaction.

HEAT OF REACTION (ENTHALPY)

Heat of the reaction (H) is the difference between the energy of the products andthe energy of the reactants.

H = Eproducts - Ereactants

For an endothermic reaction, Eproducts > Ereactants,Therefore, H is positive.


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Note: In a reversible reaction, the energy released in forming the products in theforward reaction is the same as the activation energy (EA) of the reverse reaction.

For an exothermic reaction, Eproducts < Ereactants, H is negative.

EA

H

POTENTIALEN

ERGY

Reactants

Products

EReleased

Activation Complex

Reaction co-ordinate

EA

POTENTIALENERGY

H

Reactants

Products

EReleased

Activation Complex



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The Mechanism of a Catalyst

A catalyst mechanism: the function of a catalyst is to provide an alternate route forthe reaction to take place. This route has a lower activation energy, and the rate ofthe reaction increases. A catalyst forms part of the activated complex and when this

decomposes the catalyst is released, unchanged.

The function of a catalyst is to provide an alternate route for the reaction to takeplace. This route has a lower activation energy, and the rate of the reactionincreases.

A catalyst forms part of the activated complex and when this decomposes thecatalyst is released, unchanged.

Two kinds of catalysis:o Homogenous catalyst is the same phase as the reactants.o Heterogeneous catalyst in different phase as the reactants.

Catalysts cannot cause a reaction to occur; they can only affect the rate of thereaction.

RATES SPEED OF A REACTION

When we study the rate of the reaction, we study the speed at which the reaction occurs.

Macroscopic VS Microscopic

It is important to know that no one has ever seen an atom and it is very unlikely that anyone

will see an atom in the near future.

What we see in chemical reactions is known as MACROSCOPIC observations.

What is actually happening to the atoms, we refer to as MICROSCOPIC changes. Often

MICROSCOPIC changes are just THEORY.

EA

H

Reactants

Products

EReleased

Activation Complex


P

OTENTIALENERGY

EA


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Collision Theory

A THEORY is our best explanation of what we observe right now. FACTS have been seen

and are what science has proved to be correct.

We need to understand how atoms behave. If we had magic spectacles (glasses) and were

able to see atoms moving around, we would notice the following:

Reactions take place when particles collide.

Not all collisions lead to reactions.

Those collisions that do lead to reactions are called effective collisions.

To increase the rate of a reaction, the number of possible effective collisions should beincreased.

In other words, the more often we can make atoms collide, the faster the reaction will take

place.

Factors that Influence Rate

Temperature The faster the particles move, the more likely they are to collide, so themore likely they are to react.

Pressure (only in gases) The more you push the particles together, the more likely theyare to collide, so the more likely they are to react.

Concentration (solutions and gases) the more particles squashed in per dm3, the morelikely they are to collide, so the more likely they are to react.

State of division and size of reaction surface (solids) the more particles open to bereacted with, the more likely they are to collide, so the more likely they are to react.

Catalyst the activation energy is lowered for the reaction making it easier forsubstances to react, so they react faster.

Nature of reacting substances different types of substances, by their very nature, react

at different speeds. For example, iron oxidises (rusts) relatively slowly while carbon (coal)oxidises (burns) fairly fast

Measuring Reaction Rate

If we do an experiment to establish the speed (rate) of a reaction under different conditions,we can measure how fast the reaction is proceeding in a number of different ways:

how reactants disappear or products appear

colour changes (colour cards or spectrophotometers)

concentration of ions (conductivity)

gas volume produced

mass changes volume of solid formed

Particle 1

Particle 2COLLISION


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Catalysts

A catalyst is a substance that speeds up a chemical reaction without being chemicallychanged itself. It does not form part of the product.

Catalysts make it possible for reactants to enter a new transition state that has lesspotential energy. (Lower activation energy)

Catalysts provide a new MECHANISM for the reaction. The reaction mechanism is the sequence of events at a molecular level that control the

speed and outcome of a reaction.

Types of Catalysts

Heterogeneous usually solid with gas or liquid moving over it (motor vehicle catalyticconverters)

Homogeneous usually all in the liquid phase

Enzymes very specific shaped biological molecules (lock and key mechanisms)

QUESTIONS FOR DISCUSSION:




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06-SEP 18:00 -19:00 CHEMICAL EQUILIBRIUM

STUDY NOTES

What is Equilibrium?

Reactions that take place in both the forward and reverse directions simultaneouslyare called reversible reactions.

Observable macroscopic changes stop, while microscopic changes continue asreactants change to products, and products change back into reactants.

When the rate of the forward reaction equals the rate of the reverse reaction, we saya state of dynamic equilibrium has been reached.

Le Chateliers Principle

If the conditions of an equilibrium system are changed by changing temperature,

pressure or concentration, a process takes place which tends to oppose the effect ofthe change

An equilibrium may be disturbed by changing any one (or more) of thefactors for the equilibrium.

Temperature Concentration (gases and solutions) Pressure (gases only)

Equilibrium Constant

If we look at the following GENERAL equation

The expression for the Equilibrium constant Kc will be as follows:

If A, B, C or D are solids or pure liquids, they must be LEFT OUT of the Kc expression.

When Kc has a high value, there will be proportionally more of the substance on theproduct side - we say the equilibrium lies to the product side (vice versa for a lowvalue).

Only temperature alters the Kc value for a specific reaction.

If pressure or concentration is changed, the system adjusts the product and reactantconcentrations in such a way that Kc stays exactly the same (on condition the

temperature does NOT change).


Nov 2011 P2 Question7

aA + bB cC + dD

ba

dc

B][[A]

D][C][Kc =


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09-SEP 17:00 -18:00 ELECTROCHEMISTRY & CHEMICALINDUSTRIES

STUDY NOTES

ELECTROCHEMISTRY

DIRECT TRANSFER OF ELECTRONS

Example: Zn + CuSO4 ZnSO4 + Cu

Blue clear brown

Observations: a small Zn plate placed in a blue copper sulphate solution gets covered with

a brown precipitate of copper and, eventually, the solution turns clear, and the clear solutionis zinc sulphate.

Reaction in ionic form: Zn + Cu2+ + SO42- Zn2+ + SO4

2- + Cu

Oxidation half: Zn Zn2+ + 2e- (Oxidation is a loss of electrons- OIL)

Reduction half: Cu2+ + 2e- Cu (Reduction is a gain of electronRIG)

Nett equation: Zn + Cu2+ Zn2+ + Cu

THE VOLTAIC OR GALVANIC CELL

Chemical potential energy Electrical potential energy

Example: Zn/Cu Cell:

Zinc half cell: Zinc electrode placed in a beaker containing a solution of zinc ions

Copper half cell: Copper electrode placed in a beaker containing a solution of copper ions

Salt bridge: Tube filled with ions of a very soluble salt (KNO3). Completes the internal circuit

and maintains electrical neutrality in the electrolyte solutions.

External circuit: Connecting wires that join the Zn electrode to the Cu electrode (can include

a voltmeter).

Anode where oxidation occurs Cathode where reductions occurs

Cell Notation: Zn(s) / Zn2+(1moldm-3) // Cu2+(1moldm-3) / Cu(s)


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STANDARD ELECTRODE POTENTIALS: THE TABLE

o The Table gives standard Emf values and these values were all measured understandard conditions.

o A reference electrode (standard hydrogen half-cell) was chosen, and all values are

measured relative to this.o Calculate Emf or E0cell using the equation E

0cell = E

0cathode - E

0anode

o E0cell for galvanic cells is positive ( spontaneous reactions)

ELECTROLYTIC CELLS

Electrical energy Chemical Reaction

Anode where oxidation occurs Cathode where reductions occurs

E0cell for electrolytic cells is negative ( non- spontaneous reactions)

Applications:

Recovering metal from ore (Aluminium from bauxite)

Refining / purifying gold and copper

Electroplating

Production of chlorine in the chlor-alkali industry

EXTRACTION OF ALUMINIUM FROM BAUXITE

Image from: http://lgfl.skoool.co.uk

Electrolysis of aluminium oxide is hugely environmentally un-friendly. The process uses avery large amount of electricity since the ore needs to be melted.

The cryolite is added to lower the melting point of the ore.

Carbon dioxide is formed at the anode of the electrolytic cell. Carbon dioxide is agreenhouse gas and as a result contributes to global warming.


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THE PRODUCTION OF CHLORINE

Chlorine is manufactured by the electrolysis of brine (NaCl dissolved in water).2NaCl(aq) + 2H2O(l) --> Cl2(g) + H2(g) + 2NaOH(aq)

Sodium hydroxide is produced at the same time as chlorine. We call this a by-

product). Sodium hydroxide is then used in making soap

There are 3 different types of cells:o Mercury cello Diaphragm cello Membrane cell

BATTERIES

Batteries are GALVANIC (VOLTAIC) cells. They convert chemical energy into electricalenergy through a spontaneous Redox reaction.

Cell Capacity - the ability of a fully charged battery to deliver a specific quantity of current

over a specific period of time (minutes or hours).

Q = It

where Q is measured in Amp. hours (Ah)

Cell emf - gives the voltage that the battery can provide.

- the voltage and charge together gives the amount of energy (work done)

the battery can provide.

W = VQ or W = VIt

Where W is the work done (energy transferred) and measured in Joules (J)

Primary and Secondary cells

Primary Cells - these are cells that can be discarded after use.

- they become flat and therefore, can no longer produce electrical

energy required to make an appliance work.

The Leclanche Cell

The very familiar torch battery is an example of the

Leclanche cell and is a primary cell.

Cathode - is a carbon rod running through the centre of the

cell surrounded by a paste of manganese dioxide (MnO2)

Anode - the zinc metal casing of the cell acts as the anode.

Electrolyte - a paste of ammonium chloride (NH4Cl ) and zinc

chloride (ZnCl2)


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At the anode : Zn Zn2+ + 2e

At the cathode : 2NH4+ + 2MnO2 + 2e Mn2O3 + H2O + 2NH3

Secondary cells

these are cells that can be recharged by driving a current through them

this converts electrical energy into chemical energy by reversing the chemical reaction,

i.e. the products of the reaction during discharge are reconverted into the starting

materials

At the anode : Pb + SO42- PbSO4 + 2e

At the cathode : PbO2 + SO42- + 4H+ + 2e PbSO4 + 2H2O

Overall :

Pb + PbO2 + 2H2SO4 2PbSO4 + 2H2O

FERTILISERS

In order to make fertiliser, we need to manufacture nitric acid, ammonia andsulphuric acid.All of these industrial processes make use of our understanding of equilibrium andrates.Let us investigate these industrial processes further.

The Lead Acid cell (the car battery)

Anode - lead alloy grids (Pb)

Cathode - grids packed with lead dioxide

(PbO2)

Electrolyte - dilute sulphuric acid (H2SO4)


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SULPHURIC ACID

Uses of sulphuric acid

Acts as a drying agent used by chemical engineers to mop up water.

Used as an electrolyte in car batteries (lead accumulator batteries).

Used in the recovery of metals such as uranium and copper. Used to clean metal surfaces.

Used to produce fertilisers.

THE CONTACT PROCESS

S (s) + O2 (g) SO2 (g)

SO2 (g) + O2 (g) 2 SO3 (g) (V2O5 catalyst)

SO3 (g) + H2SO4 H2S2O7

H2S2O7 + H2O 2 H2SO4

Sulphur is burnt in oxygen.

Sulphur dioxide is further reacted with oxygen in contact with a vanadium pentoxidecatalyst to form sulphur trioxide. This is a reaction that is governed by equilibriumprinciples.

Sulphur trioxide is then added to sulphuric acid (note only 1 molecule) to formpyrosulphuric acid/fuming sulphuric acid/oleum.

Pyrosulphuric acid is mixed with water and sulphuric acid is formed (note 2 molecules).One molecule of sulphuric acid is invested to make two molecules.

AMMONIA

Ammonia is produced by means of the Haber process. This process is also governed byequilibrium principles.

HABER PROCESS

N2 (g) + 3 H2 (g) 2 NH3 (g) (iron oxide catalyst) H = -46 kJ.mol-1

Temperature: Exothermic reaction. Lowering the temperature shifts the equilibrium tothe right. However, lower temperature also slows the reaction down so an optimum

temperature must be found (600 K - 800 K)

Pressure: 4 molecules on the left and 2 molecules on the right; therefore, high pressurefavours the forward reaction. (350 atm)

Concentration: Ammonia is continuously removed, to reduce ammonia concentrationand shift the equilibrium to the right.

Uses of ammonia

As a cleaning agent when dissolved in water.

In the manufacture of fertilisers. Ammonium salts are highly soluble in water so they

Can be dissolved and absorbed by plants, thus making nitrogen available to the plant.

In the manufacture of ammonium carbonate used in the textile industry.

In the manufacture of nitric acid.


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NITRIC ACID

Nitric acid is produced by the Ostwald process.

THE OSTWALD PROCESS

4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O

2 NO (g)+ O2 (g) 2 NO2 (g)

4 NO2 + 2 H2O + O2 4 HNO3

Ammonia is oxidised to nitrogen monoxide and water.

Nitrogen monoxide is further oxidised to nitrogen dioxide.

Nitrogen dioxide is then added to water from the first step and oxygen to make nitric acid.

Nitrate salts are highly soluble in water and, therefore, assist in allowing nitrogen to beabsorbed by plants.

CHALLENGES FOR THE CHEMICAL INDUSTRY

Safety issues regarding the transport of chemicals

Pollution control

Waste disposal

Energy consumption

THE FERTILISER INDUSTRY

Commercial fertilisers are described in terms of their relative proportions ofnitrogen (N), phosphorus (P) and potassium (K).

NPK numbers are printed on fertiliser bags.E.g. 5:13:5 means the content of the bag is

5% nitrogen13% phosphorus

5% potassium

Sources of potassium: Salts containing potassium are referred to as POTASH when used as fertilisers.

Mined potassium salts, such as KNO3 and K2SO4 are used.

Sources of phosphorus bone meal that was acidified to yield phosphoric acid H3PO4 mined calcium phosphate Ca3(PO4)2 Calcium phosphate is insoluble in water and cannot be absorbed by plants.

Calcium phosphate is treated with sulphuric acid to yield water solublesuperphosphate that can be absorbed.

Ca3(PO4)2 + H2SO4 2CaSO4 + Ca(H2PO4)2

EUTROPHICATION

Extensive utilisation of fertilisers leads to pollution of surface and ground water andeutrophication of lakes, dams and rivers. This is mainly due to fertiliser wash off

Eutrophication is caused by excess phosphates and nitrates in rivers, lakes and dams.

Phosphates promote the growth of algae which cover the surface of the water and killaquatic plants below.

Bacteria decompose the dead aquatic life causing oxygen levels in the water drop tosuch a low level that aquatic animals suffocate and die.


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Nov 2011 P2 Question 8, 9, 10, 11




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SPRING SCHOOL

GRADE12

PHYSICALSCIENCES

RADIO BROADCAST


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SPRING SCHOOL01-OCT 10:00 -11:00 MECHANICS

STUDY TIPS:

Print out a copy of the information sheet and make sure you know where tofind the equations and constants. This will save you time in the exam.

Make a list of laws and principles using the memos from previous exampapers or a textbook. You must learn these and be able to recall them wordfor word. There are no part marks allocated in questions that ask you to statea law or principle.

Draw a sketch diagram for each question. Fill in all the known information.Use mechanics equations to find the unknown.

Always work with SI units. Every answer must have the correct unit.

Remember the term from rest means the initial velocity is 0 m.s-1 The acceleration due to gravity, g = 9,8m.s-2, always acts down. It cannot

change direction or size. Any object falling down or thrown up experiencesacceleration downwards.

At the maximum height above the ground, the velocity of a projectile is 0 m.s -1but its acceleration is still 9,8m.s-2 downwards.

When you sketch graphs make sure you label the axes and give the SI unit.

Make sure you that when answering questions about vector quantities, youhave a positive answer, the correct SI unit and the direction in your answer.


Feb / Mar 2011 P1 Question 3 & 5

ON AIR COMPETITION QUESTION

What impulse is equal to?

A change in velocity of a body.

B rate of change of net force

C product of net force and time the force is applied

D product of mass and velocity of the body


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Diagram for Question 3 (Feb/ Mar 2011)

Diagram for Question 5 (Feb/ Mar 2011)


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02-OCT 10:00 -11:00 ORGANIC CHEMISTRY

STUDY TIPS:

You must learn the IUPAC rules for naming organic molecules. You must learn theprefixes for 1-8 carbons in a chain and the suffixes for the different homologousseries.

Make sure you can identify the functional group for each homologous series.

When you are asked to draw a structural formula of a molecule, make sure you showall the bonds. Each carbon must have 4 bonds.

A good way to practise naming and drawing is to find all the isomers of a molecularformula. Start with C5H12 and then increase the number of carbons and includedifferent functional groups.

Remember the steps of the scientific method and how to do a proper scientific

investigation. You need to be able to formulate an investigative question, state anhypothesis, identify variables, control variable, interpret results and draw aconclusion from the results.

Draw up a table of the physical properties of organic molecules, the intermolecularforces present and describe the trend for increasing chain length, increasingbranches using different functional groups.

Use flow diagrams to learn the different types of organic reactions.


Nov 2011 P2 Question 1.1, 1.2

Nov 2011 P2 Question 2.1, 2.2 and 2.3

Feb 2011 P2 Question 4

COMPETITION QUESTION

Which ONE of the following pairs of reactants can be used to prepare the ester propylethanoate in the laboratory?

A propanol and ethanoic acid

B propane and ethanoic acid

C ethanol and propanoic acid

D propane and ethanol


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Diagram for Question 4 (Feb 2011 P2)


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03-OCT 10:00 -11:00 ELECTRICITY

Study Tips:

Make sure you revise all your Grade 11 work on electrostatics, capacitors,

electromagnetic induction and electric circuits. Pay special attention to learning Coulombs Law, Faradays Law and Ohms Law. Recognise that the equations given on your information sheet describe the laws and the

relationship between the variables.

When two variables are directly proportional, if one doubles the other doubles too.

When two variables are inversely proportional, if one doubles the other halves.

For Coulombs Law, force is inversely proportional to distance between the chargessquared, (

). This means that if we double thedistance, the force will decrease by 4

times. If you want to double the force, you need to reduce the distance by 2 times Practise drawing circuit diagrams. Make sure you can identify parts of the circuit where

the current is the same (ammeter readings) and where potential difference is the same(voltmeter readings).

For electric circuit questions, there is usually more than one way to find the correctanswer. When doing previous exam paper questions, always check your answer usingan alternative method.

For electric motors and generators, make sure you can determine the direction of motion,magnetic field or current. The right hand rule is preferred for both. However some peoplestill use the left hand rule for motors and the right hand rule for generators. Select onemethod and stick to it.

Remember the electric motor has a split ring commutator and the AC generator has sliprings.


Nov 2011 P1 Question 2.6 and 2.8


Feb 2011 P1 Question 9


What is the SI unit of measurement of the rate of flow of charge in a conductor?

A watt

B volt

C ampere

D coulomb


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Diagram for Question 9 (Feb 2011 P1)


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04-OCT 10:00 -11:00 RATES & CHEMICAL EQUILIBRIUM

STUDY TIPS:

Remember the steps of the scientific method and how to do a proper scientific

investigation. You need to be able to formulate an investigative question, state anhypothesis, identify variables, control variable, interpret results and draw aconclusion from the results.

For rates of reaction you must be able to explain the how changing temperature,concentration, particle size (surface area) and a catalyst affects the rate usingcollision theory

Revise the following graphs: potential energy vs. reaction co-ordinate for exothermicand endothermic reactions, the Maxwell-Boltzmann energy distribution curve, massof reactants vs. time during a reaction, volume of gas collected during a reaction vs.time and reaction rate vs. time for reversible reactions in chemical equilibrium.

For chemical equilibrium calculations, make sure you write down the Kc expressionfor the given balanced chemical equation. Do not write down the general formula.Remember to include only the concentration of gases and aqueous solutions. Do notinclude solids or pure liquids.

For Kc calculations, make sure that all the information given is in the same units. It isbest to have all quantities in moles.

Use the RICE table to set out your work neatly. Dont forget to convert all moles intoconcentration by dividing by volume in the final step of the table.

Remember only TEMPERATURE will change the value of Kc

Revise interpreting and sketching graphs of concentration vs. time for systems inchemical equilibrium. Recognise what has caused a change in the position of

equilibrium using a graph. State and explain Le Chateliers principle.


Nov 2011 P2 Question 2.4, 2.5 and 2.6

Feb 2011 P2 Question 7.4 - 7.6


A chemical reaction reaches equilibrium. Which ONE of the following statementsregarding this equilibrium is TRUE?

A The concentrations of the individual reactants and products are constant.

B The concentrations of the individual reactants and products are equal.

C The concentrations of the individual reactants are changing continually.

D The concentrations of the individual products increase until the reaction stops.


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Diagram for Question 7.4 (Feb 2011 P2)


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05-OCT 10:00 -11:00 WAVES, LIGHT & SOUND

STUDY TIPS: Remember that frequency and wavelength are inversely proportional to each other.

A wave with a big wavelength will have a low frequency, and a wave with a smallwavelength will have a high frequency.

For sound, frequency is directly proportional to pitch and amplitude is directlyproportional to loudness.

When a source of sound moves towards a stationary observer, the frequency theobserver hears is greater than the frequency of the source (higher pitch).

When a source of sound moves away from a stationary observer, the frequency theobserver hears is less than the frequency of the source (lower pitch).

Red shift is an example of the Doppler Effect. Light from stars moving away from Earthhas a smaller frequency than expected. The line emission spectra are all shift towardsthe red end of the spectrum.

Huygens Principle is used to explain diffraction. Every set of points on a wavefrontacts as a source of wavelets. The wavelets interfere with each other to produce thenext wavefront.

Interference is evidence that light has a wave nature.

The photoelectric effect is evidence that light has a particle nature.


Nov 2011 P1 Question 2.4, 2.5, 2.9 and 2.10

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