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K-12Corpus

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In the other direction, the products react to form the reactants again

A special double-headed arrow ( ) is used to show this type of :A reversible reaction A reversible reaction is a chemical reaction that can proceed in both the forward and reverse directions

In other words, the reactants and products of the reaction may reverse roles

Remember that implies that A goes to B and cannot become A again

A can go to B and B can go to A.So, in the following reversible reaction: is the reaction.The forward reaction is always taken from the given equation and written: left to right

is the reaction.The reverse reaction is always taken from the given equation and written: right to left.Exercise 8.1See solutionsWhich of the following situations describes a closed system

The water vapour can leave the pot (system) if there is no lid

Assume that none of the solid or liquid reactants or products go into the gas phase

Initially (time = ), the rate of the is high (fast)

As the reaction gets closer to equilibrium the rate of decrease levels out until the forward reaction has a constant rate.Initially the rate of the is low (slow)

As the reaction progresses the rate of increase levels out until the reverse reaction has a constant rate.At this point the forward and reverse reaction rates are equal and this is called .Although it is not always possible to observe any macroscopic changes, this does not mean that the reaction has stopped

The forward and reverse reactions continue to take place and so microscopic changes still occur in the system

This state is called dynamic equilibrium.Dynamic equilibrium There is a dynamic equilibrium in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction

In the liquid-gas phase equilibrium demonstration, dynamic equilibrium was reached when there was no observable change in the level of the water in the second beaker even though evaporation and condensation continued to take place.For more information on dynamic equilibriums watch this video:Video: 27VJ

A different concept to strong and weak is the concept of concentrated and dilute

Thus a strong acid can be prepared as either a concentrated or a dilute solution

A solution of which the exact concentration is known is called a standard solution

A concentrated solution is one where a large amount of a substance (solute) has been added to a solvent

Note that both strong and weak acids and bases can be used in concentrated solutions

Concentrated solution A concentrated solution is one where there is a high ratio of dissolved substance (eg acid or base) to solvent

A dilute solution is one where a small amount of a substance has been added to a solvent

Note that both strong and weak acids and bases can be used in dilute solutions

A concentrated solution has a lot of solute molecules (red circles) in the solvent

A dilute solution has few solute molecules (red circles) in the solvent

Dilute solution A dilute solution is one where there is a low ratio of dissolved substance to solvent

A concentrated solution can be made from a strong or a weak acid or base

A dilute solution can also be made from a strong or a weak acid or base

Whether a solution is concentrated or dilute depends on how much of the acid or base was added to the solvent

A strong base that is also concentrated would be a base that almost completely dissociates when added to a solution, and you also add a large amount of the base to the solution

A weak acid that is also dilute would be an acid where only a small percentage of molecules ionise when added to a solution, and you also add only a small amount of the acid to the solution

The electrical conductivity of a solution depends on the concentration of mobile ions in the solution

This means that a concentrated solution of a strong acid or base will have a high electrical conductivity, while a dilute solution of a weak acid or base will have a low electrical conductivity

Therefore, the more ions (charged particles) there are in a solution, the greater the electric current that can be conducted through the solution by the charged particles

These include ions in solution and ions in melted ionic materials

Only a small percentage of the molecules dissociate in the solution

Almost complete ionisation or dissociation means an acid or base is strong

Only a small amount of ionisation or dissociation means an acid or base is weak

Almost all the molecules ionise in the solution, therefore is a strong acid

Only a small percentage of the molecules dissociate, therefore is a weak base

A concentrated solution has a high ratio of solute to solvent

A dilute solution has a low ratio of solute to solvent

This is a high ratio, therefore the solution of is concentrated

This is a low ratio, therefore the solution of is dilute

Only a small percentage of the molecules ionise in the solution

Almost complete ionisation or dissociation means an acid or base is strong

Only a small amount of ionisation or dissociation means an acid or base is weak

Almost all the molecules dissociate in the solution, therefore is a strong base

Only a small percentage of the molecules ionise, therefore is a weak acid

A concentrated solution has a high ratio of solute to solvent

A dilute solution has a low ratio of solute to solvent

This is a low ratio, therefore the solution of is dilute

This is a high ratio, therefore the solution of is concentrated

To do that the molar mass (M) needs to be calculated

M() = ( x ) + + ( x ) =

To do that the molar mass (M) needs to be calculated

For every mole of a solvent there are moles of lithium hydroxide ()

There are many more moles of the base than the solvent

For every moles of a solvent there are moles of nitric acid ()

There are many more moles of the solvent than the acid

% of an unknown acid donates protons when the acid is added to water

This means that it almost completely forms ions in solution and is therefore a strong acid

Is a solution with a pH of strongly or weakly acidic

Although this is a strong acid the solution is only weakly acidic

This means that there must be a very small number of moles of the acid in the total volume of the solution

You need the number of moles (n) and the molar mass (M)

You need the number of moles (n) and the molar mass (M)

You have the volume (V) and original concentration of the ammonia solution, you need number of moles (n) in that original solution

Therefore n = C x V n(original solution of ) = x =

The final volume used to calculate the concentration must be the volume of the water plus the volume of ammonia added

The study of electrical circuits is essential to understanding the technology that uses electricity in the real-world

In this chapter we will focus on revising content from Grade 11 and extending our understanding of the internal structure of a battery/cell and how this influences what you already know about circuits.Units and unit conversions- Physical Sciences, Grade 10, Science skillsCircuit components- Physical Sciences, Grade 10, Electric circuitsOhm's law - Physical Sciences, Grade 11, Electric circuitsSeries and parallel components - Physical Sciences, Grade 11, Electric circuitsEquations - Mathematics, Grade 10, Equations and inequalitiesSeries and parallel networks of resistors:Understanding of Ohm's Law.The meaning of conservation of charge and energy for different types of circuits.Calculations done using series and parallel circuits.Solve problems involving current, voltage and resistance for circuits.Batteries and internal resistance:State that a real battery has internal resistance.Definition of a load.Do experiments of finding the internal resistance of a battery.Do calculations by using circuits with batteries with internal resistance.Evaluating internal resistance in circuits:Solve circuit problems using batteries with internal resistance with series, parallel and series-parallel circuits.Extension: Wheatstone Bridge:Definition of a Wheatstone Bridge.Solve problems concerning the Wheatstone Bridge.Units and unit conversions- Physical Sciences, Grade 10, Science skillsCircuit components- Physical Sciences, Grade 10, Electric circuitsOhm's law - Physical Sciences, Grade 11, Electric circuitsSeries and parallel components - Physical Sciences, Grade 11, Electric circuitsEquations - Mathematics, Grade 10, Equations and inequalities

In Grade 11 you learnt how a magnetic field is generated around a current-carrying conductor

You also learnt how a current is generated in a conductor that moves in a magnetic field or in a stationay conductor in a changing magnetic field

This chapter describes how conductors moving in a magnetic field are applied in the real-world.Today, currents induced by magnetic fields are essential to our technological society

The ubiquitous generator—found in automobiles, on bicycles, in nuclear power plants, and so on—uses magnetism to generate current

Other devices that use magnetism to induce currents include pickup coils in electric guitars, transformers of every size, certain microphones, airport security gates, and damping mechanisms on sensitive chemical balances

Not so familiar perhaps, but important nevertheless, is that the behavior of AC circuits depends strongly on the effect of magnetic fields on currents.Electrical machines - generators and motors:State the difference between generators and motors.Definition of Farady's Law.Using Farady's Law for explanations.Definition of a generatorExplaining the principle of an AC and DC generator using words and pictures.Explaining the difference between AC and DC generators.Explains what happens when a current carrying coil is placed in a magnetic field.Explaining the principle of an electric motor using word and pictures.Definition of Lorent Force.Examples of AC and DC generators and the use of motors.Alternating current:Explaining advantages of alternating current.Write different expressions.Definition of the root mean square values and explains why they are useful.Calculations done on the average power.Drawing of graphs.Solve different kinds of problems using alternating current.

Many people are using solar power as a source of energy for their homes

Solar power can be used to heat water or to supply electricity

Have you ever wondered how solar energy is converted to electrical energy

In this chapter, we examine the process that is used to achieve this energy conversion.Video: 27Z3Units and unit conversions - Physical Sciences, Grade 10, Science skillsEquations - Mathematics, Grade 10, Equations and inequalitiesElectronic configuration- Physical Sciences, Grade 10, The atomElectromagnetic radiation- Physical Sciences, Grade 10, Electromagnetic radiationPhotoelectric effect:Description of the photoelectric effect.Give the significance of the photoelectric effect.Definition of the cut-off frequency.Definition of the work function and that it is material specificThe relationship between the cutt-off frequency and maximum wavelength.Calculations using the photoelectric equation.Knowing the relationship between the number of electrons and intensity of the incident radiation.Understanding the nature between the photoelectric effect and the particle of nature of light.Emission and absorption spectra:Explanation of the source atomic emission spectra and their unique relationship to each element.Relation between the atomic spectrum and the electron transitions between energy levels.Explaining the difference between atomic absorption and emission spectra.Applications of emission and absorption spectra.Units and unit conversions - Physical Sciences, Grade 10, Science skillsEquations - Mathematics, Grade 10, Equations and inequalitiesElectronic configuration- Physical Sciences, Grade 10, The atomElectromagnetic radiation- Physical Sciences, Grade 10, Electromagnetic radiation

An easy way to remember this is:In both oxidation and reduction a transfer of electrons is involved resulting in a change in the oxidation state of the elements

In each of the following reactions say whether the reactant iron species (, , ) is oxidised or reduced

This section studies the use of resources, more specifically phosphate rock, natural gas and other gases (like nitrogen and oxygen) to produce fertilisers to sustain a food supply for people on Earth

The industrial processes that are involved in the manufacturing of fertilisers are studied

The purpose of studying this industry is to make learners aware of the impact of human activities on the environment and our responsibility to use our resources sustainably.Prior knowledgeThis section of work is done at the end of the Grade 12 year and provides an ideal opportunity to revise some of the concepts covered in redox reactions, rates and extent of reactions, acid-base reactions and balancing of equations

The prior knowledge for this chapter includes a general awareness that the chemistry that is done at school has application in industrial processes in South Africa and elsewhere

Two examples that would have been covered in the electrochemistry section, namely the production of chlorine and the recovery of aluminium metal from bauxite, can provide a useful context to study further application of chemistry in real life

Furthermore, this section also builds on learners’ prior knowledge of the lithosphere and how we are using these resources on Earth.PlanningCAPS allocates 6 hours for this section

The suggested lessons can be adapted, depending on the length of the lessons at your school and how much time you have to teach the section

Introduction to the importance of nutrients This section covers the importance of nutrients and is necessary to understand the role of fertilisers

In this lesson learners should do the concept map activity as a way of summarising the information

Learners should start on the investigation of fertiliser use in their area from this first lesson, as it is a long investigation and requires a community survey

The role of fertilisers In this lesson the role of fertilisers should be covered

This includes an understanding of the NPK ratios and the specific nutrients found in different fertilisers

The industrial preparation of fertilisers This section covers the industrial production of chemicals used in inorganic fertilisers

At the end of the section there is a worksheet for the learners to complete

The worksheet, as well as the answer sheet is provided in this book

This is a long section and, if time allows, should be covered over three lessons

Alternative sources of fertilisers In this lesson learners should understand and be able to name alternative sources of fertilisers