C8 Organic Chemistry

Fossil fuels

Fuels are substances that react with oxygen to release energy in exothermic combustion reactions.

Coal forms from remains of plants and crude oil forms from animals and bacteria in oceans and lakes. They were not able to rot without regular oxygen. Intense pressure and heat resulted in their formation over millions of years. All release energy upon burning.

Coal, natural gas and petroleum are fossil fuels that produce carbon dioxide in combustion.

Natural gas is mainly made of methane.

Petroleum is a mixture of hydrocarbons. It is separated into useful fractions by fractional distillation.

 

Combustion

Complete Combustion: CnHn + O2 → CO2 (g) + H2O (g) using a hydrocarbon fuel

Incomplete Combustion: CnHn + O2 → CO (g) + H2O (g) carbon monoxide is poisonous!

Incomplete combustion happens when there is a lack of oxygen.

 

Fractional distillation

Separates liquids using different boiling points, and hydrocarbons have a range of boiling points due to impurity. Small, volatile, low-boiling point molecules that flow easily and ignites easily has less intermolecular attractive forces and hence takes less energy to seperate, they will be at the top of the fractional distillation columns. Big molecules with higher boiling points has more intermolecular attractive forces and takes more energy to separate, and they settle at the bottom of fractional distillation columns.

 

Distillation of crude oil (petroleum)

Name	Boiling point	# of carbons	Uses
Refinery gases	20°	1-4	Bottled gas for heating and cooking
Petrol/Gasoline	70˚	5-10	Car fuel
Naphtha	120˚	8-12	Chemical uses
Kerosene	170˚	10-16	Jet fuel
Diesel oil	270˚	16-20	Big car fuel/ diesel engines
Fuel oil	260-340˚	30-40	fuel
Bitumen	340˚	50+	Road building

 

Alkanes

They are homologous family of hydrocarbons with similar properties.

They are saturated combustible fuel that has single bonds. Generally unreactive except when burning.

Generic formula: CnH2n+2

Methane, ethane, propane, butane, pentane, hexane, etc.

 

Alkenes

They are unsaturated hydrocarbons with one double bond between 2 carbon atoms. They are more reactive as double bond is less stable.

CnH2n

Ethene, propene, butene, pentene, hexene, etc.

 

Cracking

Cracking produces alkenes. It’s a chemical reaction that breaks down long hydrocarbons into smaller ones, produce is random.

Large moleculed alkane /longer alkane → shorter alkane + alkene

Conditions: aluminum/silicon (3) oxide catalyst (porcelain catalyst), high temperature and pressure

 

Bromination of ethene / test for unsaturation

C2H4 + Br2 → C2H4Br2

Bromine is brown-yellow solution that when shaken with ethene will turn colorless very fast at room temperature.

Product is bromoethane. If the solution remains colored, then hydrocarbon is an alkane.

This is an addition reaction.

 

Hydrogenation of ethene / addition reaction

C2H4 + N2 → C2H6

Hydrogen is added across the double bonds to make it a saturated alkane, increasing the melting point. A nickel catalyst is used. 150°C Temperature.

 

Hydration of ethene / addition reaction

C2H4 + H2O → C2H6O

Adding water turns ethene into ethanol/alcohol. This is purer than fermentation, and product is used in medicine and science. Phosphoric acid is a catalyst, and under heat and pressure.

 

Alcohol

Complete combustion: C2H6O + 3O2 → 2CO2 + 3H2O

Ethanol is widely used as a solvent in many perfumes and cosmetics and as a fuel.

 

Polymerizations

Macromolecules are large molecules built up from smaller units (monomers) and they have different units for different macromolecules.

There are two ways to make a polymer:

Addition: monomers bond and rearrange, no atoms are lost.

2000 atm, 200˚C and O2 impurity.

 

Ethene		Polythene
Propene		Polypropylene
Vinyl chloride		Polyvinyl chloride

These are used in making plastics.

 

Condensation polymerization: Molecules (usually water) are lost as byproducts.

Nylon is made from reacting diamine with dicarboxylic acid. Water is produced. This is called a polyamide as it is joined up by amide links as pictured.

Reversible under alkaline or acidic conditions.

 

Natural macromolecules

Protein has the same amide linkages like nylon but they are formed with amino acids.

Proteins can be hydrolysed to amino acids under acid or alkaline conditions.

 

P5 Heat and Particles

Matters of state

• Solids: tightly packed, in a regular pattern, strong intermolecular forces, fixed volume, fixed mass, fixed shape, cannot flow, cannot be compressed.
• Liquid: close together with no regular arrangement, molecules touching, medium forces of attraction, has fixed volume and no determinate shape, take the shape of their container, cannot be compressed.
• Gas: Moving in all directions very quickly, no longer bond by intermolecular forces, occupies all the space, has the most kinetic energy, can be compressed.
• When heat is added, the energy is used to overcome the attractive forces between molecules of solids, liquids and gases to change their state. There is no change in overall kinetic energy and hence no temperature increase. The heat used in this process is called latent heat of vaporization or latent heat of fusion.
• 热胀冷缩。
• Everyday applications include leaving gaps between railroads so in heat expansion won’t cause it to break, pipes may be destroyed when cooled excessively, etc.

Density

• Density equation: Mass / volume
• Irregularly shaped solid calculations can be done using water, measuring cynlinder, etc.

Collision Theory

• • Temperature is just how fast the molecules are vibrating, how much kinetic energy they have.
  • The motion of the molecules will be faster when temperature is higher. exert more frequent collisions / collide at greater speed, with tyre wall, more force exerted on tyre walls.

 

• Pressure and volume: P1V1 = P2V2

 

Evaporation

• Skin/body gives the molecules energy.
• Evaporation is the escape of the most energetic molecules from the surface of a liquid.
• Evaporation leads to consequent cooling as it takes the energy away from the body that it escaped from.
• Higher temperature, higher surface area and higher air flow means more evaporation.

Heat transfer

• • Put rods of different materials above a bunsen burner. Apply wax to the ends of the rods, whichever rod with the wax melting faster is the best conductor.
  • Heat transfer in solids by conduction happens when adjacent atoms vibrate against one another and pass on energy.

 

• Conduction is  microscopic collisions of particles and movement of electrons within a body.

• Metals are the best conductors

 

• • Applications: cooking, heating a tin, etc.

 

• Convection is the main method of heat transfer in fluids(liquids and gases)

• Hot air rises, cold air falls

 

• • Heat makes the air less dense
  • Experiment: put a lighted candle wisk and see the smoke go with the hot air rising
  • Applications: boiling water, air con

 

• Radiation transfers heat and does not require a medium to travel through

 

• • Measure temperatures to show good emitters and good absorbers of infrared radiation like black, dull, matt, and bad emitters and bad absorbers are white, shiny.

 

• Infra-red radiation is the part of the EM spectrum that gets involved in radiation

 

• Application: Radiators in cars and stuff are painted black so produce cooling effect.

Thermal capacity

• • Thermal capacity is amount of heat taken to change the temperature of an object.
  • Temperature is a measure of how hot something is in degrees
  • Heat is a measure of the thermal energy contained in an object in Joules

 

• Specific heat capacity is amount of energy needed to change the temperature of 1 kg of the substance by 1°C.

• Equation: Energy (joules) = mass(kg) * specific heat capacity (c) * △Temperature (°)

 

Melting and boiling

• • Melting is the process by which heat supplied to a solid turns it into a liquid.
  • Melting point/boiling point is the temperature at which it changes state.
  • Boiling is the process by which heat supplied to a liquid turns it into a gas.
  • Melting and boiling happens without a change in temperature.
  • Boiling happens at the boiling point, happens throughout the object, is fast, and usually needs a source of energy.
  • Evaporation happens at all temperatures, is slow, only at the surface, and takes energy from the surroundings.

 

• Condensation is the reverse of vaporisation and the conversion of a vapour or gas to a liquid.

 

Solidification/freezing is the reverse of melting and the conversion of a liquid to a solid.

P4 Waves

Waves

 

• Wave motion transfers energy without transferring matter in the direction of wave travel.

• A wave is an oscillation, such as ropes and springs and water waves.

• Transverse waves are waves whose direction of oscillations is at right angles to the direction of propagation(direction.) e.g. Electromagnetic waves. It has troughs and crests.

• Longitudinal waves are waves whose direction of oscillations is parallel to the direction of propagation. E.g. Sound waves. It has compressions and rarefactions.

• Speed is how fast a wave is traveling.

• Wavelength is the distance between successive crests of a wave.

• Amplitude is the maximum extent of a vibration or oscillation, measured from the position of equilibrium; absolute value of displacement.

• Frequency is the number of complete waves passing a given point in one second, measured in Hertz (Hz).

• Wavefront is a line joining neighbouring points which are in phase.

 

• • Normal: the line perpendicular to the surface at the point of incidence.

 

• Speed (m/s) = frequency (Hz) * wavelength (m)

 

Wave reflection and refraction

• • Reflection of wave in a smooth plane barrier: Angle of incidence = Angle of reflection
  • A change in wavelength may cause light to change direction and speed

 

• Refraction is a deflection of wave passing obliquely through the interface between one medium and another or through a medium of varying density.

 

• Water waves travel faster in deep water than in shallow.
• Experiment to determine refraction: use glass block to show.

Sound waves

• • Sound waves are produced by vibrating sources which causes the medium around it to vibrate.
  • Sound waves are transmitted by compressions and rarefactions.
  • Sound waves must need a medium to travel, it is a mechanical wave.

 

• Human range of audible frequencies: 20 to 20,000 Hz

 

• • Using data logger and long distances to measure speed of sound in air
  • Sound travels fastest in solids, then liquids, then air because molecules are packed tighter.

 

• Louder sound has higher amplitude.

• Higher pitch has higher frequency.

 

• Echo is a reflection of sound that arrives at the listener with a delay after the direct sound, the delay is proportional.

Electromagnetic spectrum

• All are transverse waves
• All travel through vacuum
• All travel at light speed of 300,000,000 m/s

 

Wave	Function
Radio waves	Radio and television communications
Microwaves	Satellite tv and telephone communication, cookimg
Infrared	Remote controllers for tv and intruder alarms
X-rays	Medicine and security

X-rays can cause cancer as they can make cells mutate. Hence, dosage of waves must be kept small.

Microwaves make water vibrate and hence cells may be damaged by the heat energy given by the microwaves.

 

Light waves

• • Optical fibres can carry information coded in light or infrared signals, and they are used in medicine to transmit image and in communications to transmit data.
  • Optical fibres has light undergo total internal reflection.
  • Critical angle: the angle of incidence for which the angle of refraction is 90°.

 

• Total internal reflection: the wave cannot pass through by refraction and is entirely reflected, and this is when angle of incidence is beyond the critical angle.

• Principal focus: The point labeled F on the diagram, where the light rays come together to form a real image.

 

• Focal length: the distance between the centre of a lens or curved mirror and its focus.
• When the object is located at the focal point, no image is formed.
• When object is beyond 2F, image will be inverted, small and real
• When the object is located at 2F, image will be inverted at 2F.
• When object is between 2F and F, image will be enlarged, inverted and real.
• When object is located in front of the focal point, image will be virtual, enlarged and upright.
• All light rays should pass the focal point somehow on ray diagrams.

 

Dispersion

Dispersion is when white light passes through a prism and splitted into a spectrum.

Dispersion happens because the different spectral colours travel at the same speed in a vacuum, but at different speeds in a medium such as glass. Amount of bending increases as change in velocity increases.

P4 Equations:

• • Wave Speed (m/s) = frequency (Hz) * wavelength (m)

 

• Reflection: Angle of incidence = Angle of reflection

 

 

C7 Reactivity

C7 Reactivity

Reduction and Oxidation

Oxidation Is Loss Reduction Is Gain

Reduction is : 1. Loss of oxygen (covalent bonds)

2. gain of electron (ionic)

The reduced compound is an oxidizing agent

Oxidation is : 1. Gain of oxygen (covalent bonds)

2. loss of electron (ionic)

The oxidized compound is a reducing agent

 

Reactivity with Oxygen

Oxidation reactions – Cu + O2 → CuO, glow + slice flame

Mg + O2 → MgO white flames

Combustion reactions – CnHn + O2 → water + CO2 flames and stuff

 

Reactivity series

K←Na←Li←Ca←Mg←Al←C←Zn←Fe←H←Cu←Ag←Au

Possibly nicer livers can magnetize almonds cars,

zero-fee hype cures silvery golds

 

Metal extraction

Ore is economically viable containing metal rocks. Rock contains metals but not that worthwhile.

1. If metal ore is less reactive than carbon…
   1. Reduce metal with carbon to extract.
2. If it is more reactive
   1. Use electrolysis to split ions.

Alloys are formed to merge several desirable qualities of the different metals. Since lattice structure is disrupted by impurities, boiling point decreases as bonds are weaker.

 

Electrolysis

Electricity pass through electrodes to extract metals. Cations are at cathode and anions go to anode. Electrolyte is the solution that conducts electricity.

Half equations:

Cations: Pb2+ + 2e– → Pb

AnionsL 2Cl– → Cl2 + 2e–

1. 1. Separating seawater: Aqueous sodium hydroxide, hydrogen at cathode and chlorine at anode, sodium hydroxide is leftover – liquid NaCl won’t have leftovers.
   2. Industrial uses include: chlorine for swimming pool disinfectant and cleaning products, sodium hydroxide for stock chemical (strong alkali) and soap, hydrogen for haber process and margarine.
   3. Separating aluminum oxide: Al2O3, aluminum ore called bauxite, can be used to extract aluminum which is lightweight resistant to corrosion and used in airplane and bikes. Cryolite added to lower melting point. Al sinks to the bottom, produces aluminum and oxygen.

 

• molten lead(II) bromide, lead at cathode and bromine at anode

• aqueous copper chloride – copper at cathode and chlorine at anode

• dilute sulfuric acid – hydrogen at cathode and oxygen at anode

• Generally: metals or hydrogen form at cathode and non-metals form at anode.

 

Electrodes can be active or inert. Inert electrodes like graphite are not involved in the reaction and actibe electrodes are involved in reaction. Such as copper plating. Anode will become thinner and cathode thicker, and hence it is used to plate objects and remove impurity, electrolyte usually contains the same ion as anode.

Hoffman Voltameter is used to collect gas from electrolysis, such as water.

 

Blast furnace

Used to extract iron.

1. Add materials: hematite, coke(impure carbon as reducing agent), limestone to remove impurities
2. Make the reducing agent stronger: Carbon must become carbon monoxide
   1. C + O2 → CO2
   2. CO2 + C → CO
3. Reduce the iron:
   1. Fe2O3 + 3CO → 2Fe + 3CO2,
4. Remove impurities
   1. CaCO3 → CaO + CO2
   2. CaO + SiO2 (sand) → CaSiO3 (slag, used in road building, neutralizsation reaction)
5. 1000C and 2000C degrees

 

Rust

Rust is the specific corrosion of iron by oxidation to iron (3) oxide. Salt speeds up rusting and both oxygen and water are needed to produce hydrated iron oxide in a redox reaction.

Surface protection means covering iron to stop water/oxygen from entering, using oil, paint and wax. Specifically, galvanizing means coating with zinc.

Sacrificial protection puts a metal attachment of metals more reactive than iron like zinc and magnesium so water and air reacts with it first.

P6 Electromagnetism and Energy Resources

P6 Electromagnetism and Energy Resources

 

Magnetic effect of current

• Magnetic pattern around straight current carrying wire
• Magnetic pattern around solenoid
• Use right hand rule to figure out (thumb’s up)
• Relay switches use the effect to reduce danger as a circuit can turn on another circuit.
• Increasing current magnitude results in stronger magnetic field proportionally.
• Reversing current direction results in:
  • D.C. North south pole reversed
  • A.C. constantly changing direction of flow.

Motor effect

• A current-carrying wire experiences a force in the presense of a magnetic field.
• A force will be creted and the wire’s movement will confirm the effect.
• Practical applications can be loudspeakers and electric motors.
• Left hand rule for movement, field, current
• Reversing current reverses direction of force.
• Reversing field direction reverses direction of force.
• Force size is the greatest when wire is perpendicular to field.
• No force if wire is parallel to field.

 

D.C. motor

• • Converts electrical energy to kinetic energy.
  • There is no current in coil when it’s 90 degree vertical, but it keeps moving due to kinetic energy.
  • A current carrying coil experiences a turning effect in a magnetic field.
  • The right side always causes a downward force.

 

• Commutators also rotate as it reverses current every 180 degree so the movement continues.

• Brushes are made of carbon and they conduct the current to complete the circuit.

• Increase # of turns in coil results in faster movement as there is a stronger magnetic field.

 

• Increase current results in faster movement as there is a stronger interaction with the field.

 

Inducing electromotive force

• Set up magnets and a wire with ammeter, move wire up and down and there will be readings on the ammeter.
• EMF is induced when there is charge in the magnetic field and it’s proportional to charge per second.
• Wire cuts field lines results in small voltage to be induced.
• Moving the wire faster, using stronger magnet, having more coils all increase the EMF.

 

A.C. Generator

• Transforms kinetic energy to electrical energy.
• Slip rings conduct electricity, and the induced current reverses every half turn.

 

Transformers

• • A basic soft iron cored transformer is used to transform voltages.

 

• Step-up transformers increase voltage from primary to secondary.

• Step-down transformers decrease.

 

• Calculation of voltage transformed: Vp/Vs = Np/Ns where N is number of coils.
• Power in equals power out for 100 efficiency: V1I1 = V2I2
• Calculating efficiency: energy input/useful energy output * 100%
• Efficiency is the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in
• Uses A.C. due to constant change of voltage.
• A.C. current changes, and magnetic field changes to induce a voltage in secondary coil.
• Electricity is transferred through long distances over wires. When current flows, wire is warm and this wastes energy. (P=I2R)
• When voltage is high, current is kept small, and there is less heat loss.
• Transformers bridge the gaps between electrical cables and home use, reduces danger.

 

Energy

• • Sun is the source of energy for all our energy resources except geothermal and nuclear.
  • Energy is released by nuclear fusion in the sun.

 

• Renewable energy is naturally replenished on a human timescale.

• sunlight, wind, rain, tides, waves, and geothermal heat,

 

• • Non-renewable energy comes from sources that will run out or will not be replenished in our lifetimes.
    • Nuclear, coal, fossil fuels

 

• Electricity can be obtained from…

 

 

Source	Advantages	Disadvantage
Chemical in fuel	readily available relatively cheap Not reliant upon the weather.	highly polluting global warming acid rain. Oil spillages
Water (Waves, tides, dams)	No pollution Costs of running are low Efficient for small islands Good energy storage	High initial cost Unreliable energy output Infrastructure hard to put in
Geothermal	Freely available No environmental impact	Drilling down has high cost
Nuclear fission	Non-renewable Radioactive waste disposal difficult	Creates a lot of energy at once
Heat and light from sun	Reliable source when sun is out Small running costs No pollution	Initial cost very expensive Not very efficient Dependant on sun.

P7 Atomic and Nuclear Physics

Nucleus

Nucleus is composed of protons and neutrons.

Isotopes are multiple forms of the same element containing different numbers of neutrons.

Isotopes can be used to treat cancer, in radiation, etc.

 

Radioactivity

 

• Background radiation is ionizing radiation at an environment that doesn’t come from deliberately introduced radiation materials. Could be naturally occuring radioactive elements, cosmic radiation and fallout. It is always there and measured.

• Radioactive emissions occur randomly over space and time as particles decay.

• Radioactive decay is the process by which an unstable atomic nucleus loses energy and emits radiation to become another element.

• Half-life is the the time taken for the radioactivity of a specified isotope to fall to half its original value. Equation: n*(½)^t

• Detecting radioactivity: Geiger-muller tube and ratemeter counts number of pulses per second. Scaler keeps running total of number of counts

 

 

Alpha, beta, gamma rays

 

	α particles	β particles	Y rays
Charge	+2	-1	Not charged
Mass	4 amu	negligible	none
Nature	Helium nucleus (2 protons, 2 neutrons)	Electron (e-1)	Electromagnetic radiation, short wavelength
Stopping it	A sheet of paper, or 10 cm of air.	Few mm of aluminum	Thick lead or concrete
Range in air	Within centimeters	A meter	High
Ionizing ability	Very strong	Weaker than a, but still ionizing	Weak

 

• Alpha decay equation: AZX → A-4Z-2Y + 42He
• Beta decay equation: AZX → AZ+1Y + 0-1e(β)
• Gamma decay is simply loss of energy.   

 

Electric and Magnetic Field effects

Positive attracts negative beta particles and negative attracts positive alpha particles, while gamma rays pass uneffected. The same goes on in magnetic fields.

 

Beta deflects more than alpha because it has a larger mass.

 

Safety

• • Hazards of ionizing radiation:
    • Damagement of living cells causing cancer
    • Affecting DNA and causing mutation

 

• Minimizing hazards:

 

• • Handling: Using tongs used to pick up sources
  • Protective clothing worn by those who work with radioactivity
  • Storage: Sources are kept in lead-lined containers
  • Usage: Sources are never pointed at people
  • Exposure times are limited

 

P7 Equations

• Alpha decay equation: AZX → A-4Z-2Y + 42He
• Beta decay equation: AZX → AZ+1Y + 0-1e(β)
• Half life equation: n*(½)^t

P3 Electricity and Magnetism

P3 Electricity and Magnetism

Magnets

• • Properties: Opposite (unlike) poles attract, and like poles repel.
  • Attracts iron, cobalt and nickel.
  • Magnetic field lines around a bar

 

• Iron is not a permanent magnet, but steel is.

 

• • Permanent magnets are made from a “hard” magnetic material that maintains its magnetism over long periods of time. They are used to hold up pictures, stick things, trains, cars, maglev.

 

• Electromagnets are made by wrapping coil around ‘soft’ magnetic material and passing a current through it – this involves electricity.

 

• Induced magnetism happens when unmagnetized magnetic material is brought near to the pole of a permanent magnet. When they attract, the material becomes a magnet itself.

 

Electricity

 

• Current is a flow of electric charge carried by electrons. Measured in amperes(A).

• Potential difference is the amount of electric potential, the amount of work needed to move a unit positive charge. It’s the observed difference in voltage between any two points in an open circuit. This is measured in volts(V).

• Electromotive force is the voltage developed by an electrical source – at the battery. It is the energy supplied by a source in driving charge around a complete circuit. Measured in volts.

• Resistance is the degree to which a conductor opposes an electric current through that conductor. Measured in ohms(Ω).

• Charge is measured in coulombs(C) which is the charge passing any point in a circuit when a steady current of 1 ampere flows for 1 second. They can be positive or negative.

 

Charges

 

• Electrical conductors is where electrons can flow freely across particles. Typical ones include metals like copper and steel.

• Insulators inhibit the free flow of electrons and can stop charges from flowing. Typical ones include non-metals like glass, plastic, rubber.

• Electric field is a region in which an electric charge experiences a force.

 

Currents

• Current is related to the flow of charge. In metals, currents happen due to a flow of electrons.
• Potential difference is what drives the current between two points in a circuit.
• Conventional current is fake as it thought that it is the positive charges that move. Electron movement carry negative charge, usually from right to left in a diagram.

Resistance

 

• A higher resistance means less current.

• A higher voltage(potential difference) means higher current.

 

• Experiment: measure voltage and current in a circuit using voltmeter and ammeter to determine resistance.

Resistance in wires

The following are directly proportional or inversely proportional. Forms straight lines.

Wire	Length	Thickness
Higher resistance	Longer wires	Thinner wires
Lower resistance	Shorter wires	Thicker wires

 

Stranger danger electric makers

• • Damaged insulation: if rubber insulator around a wire is broken, electricity could pass out to a human body causing electric shock and electric fire.

 

• Overheating of cables: if a large current goes through or if something short circuits, high temperatures in wires could melt the insulation and cause electric fire.

• Damp conditions: water is a conductor and can cause electric shock. Plus, body’s resistance lowers in damp conditions.

• Fuses: thin wires that heats up to melt and stops the flow of current.

 

• • • Its rating should be slightly higher than the one the device uses. I.e. 5A fuse for a 3A thing.

 

• Circuit breakers are push switches that use electromagnets like soft iron to break the circuit in case of too much current.

 

Series and parallel circuits

• In a series circuit…
  • The current at every point is the same.
  • Sum of voltages across component is equal to total voltage in supply.
  • Combined resistance of resistors are added.
• In a parallel circuit…
  • Current from the source is larger than current in each branch.
  • The combined resistance of 2 resistors is less than that of either by itself.
  • Connecting lamps in parallel allows you to switch them off and on separately.
  • Current from the source is the sum of currents in separate branches.

Circuit components

 

• Input transducer is a sensor that changes energy from one form to another, in this we learn about LDR and thermistors.

• Light dependent resistors(LDR) increases resistance when it’s in the dark.

• Thermistors increase resistance when temperature is low.

 

• Circuits can operate as light sensitive switches and temperature operated alarms during relays.

P3 Equations:

• • Current: I(amps) = Q(coulombs) / t (seconds)

 

• Energy: E(joules) = I(amps) x V(volts) x t(seconds)

• Power: P(watts) = E/t or IV

• Resistance:  R(ohms) = V(volts) / I(amps)

• Total resistance in series circuit: RT = R1 + Rn

• Total resistance in parallel circuit: 1/RT = 1/R1 + 1/R2

 

 

C6 Detective Chemistry

C6 Detective Chemistry

Testing for water

1. Add anhydrous copper sulfate (will turn from white to blue)
2. Use cobalt chloride paper (will turn from blue to pink)

Purification of water

Water is purified

1. First by filtration, to remove any insoluble particles, being sprayed onto specially prepared layers of sand and gravel. As it trickles through, different sized insoluble solids are removed. The filter beds are cleaned periodically by pumping clean water backwards through the filter.
2. Second by chlorination to kill any bacteria.

Uses of water

1. Industry: becoming a chemical solvent, use in cosmetics and food, etc
2. Home: drinking, bathing, cooking, etc

Separating gases in air

1. 1. Cool air into a liquid.
   2. Heat gradually and use fractional distillation to separate gases at their different boiling points.

 

• Nitrogen has the lowest boiling point, hence it is collected first.

 

Test for gases

Oxygen	Will relight a glowing splint.
Hydrogen	Burning splint goes out/explodes with a squeaky pop
CO2	Bubble through limewater, will form white precipitate
Ammonia	Turns damp red litmus → blue (due to alkalinity)
Chlorine	Turns blue litmus red and ultimately bleaches it (due to acidity)

Flame tests

1. Put clean wire into HCl.
2. Dip wire into solid you want to test.
3. Hold wire in flame.

Sodium will burn yellow, potassium will burn lilac, copper will burn green.

 

Test for cations

 

	Sodium hydroxide (aq)	Ammonium hydroxide (aq)
Ammonium (NH4+)	Ammonia gas upon warming with NaOH, will turn damp red litmus paper blue. basic.	N/A
Copper (II) Cu2+	Light blue ppt insoluble	Dark blue ppt soluble
Iron (II) Fe2+	Green ppt insoluble in excess
Iron (III)Fe3+	Red/brownish ppt insoluble in excess
Zinc (II) Zi2+	White ppt soluble in excess turns colorless

 

Test for anions – white precipitates

	Acidification and reaction
Carbonate (CO32-)	Add HCl which produces CO2 and water. Bubble through limewater for white precipitate.
Chloride (Cl–)	Acidify with nitric acid, then react with silver nitrate White precipitate purple in sunlight, silver chloride insoluble
Sulphate (SO42-)	Acidify with HCl and react with barium chloride White insoluble barium sulphate ppt
Nitrates (NO3–)	Reduce nitrates into ammonia first Use aluminum catalyst to test for ammonia.

 

Methods of separating mixtures

1. 1. Filtration for insoluble solid and liquid. Filter through paper to separate filtrate from insoluble residue.

 

• Crystallization for soluble compounds and saturated solutions. Evaporate one product and find the other product left in the basin.

• Chromatography for separating soluble mixtures of liquids using difference in solubility.

• Distillation for separating soluble liquids through difference in boiling point. Both vapor and liquid can be collected. Vapor can be condensed.

• Fractional distillation for separating more than one liquids at different boiling points at different columns.

 

 

P2 Work, Energy and Power

P2 Work, Energy and Power

 

Work

• Work done is related to the magnitude of a force and the distance moved.
• Energy transfer can occur. E.g Gravitational potential energy can be gained.
• Work done (N/J) = Force (N) * distance (m)

 

Power

• Power is related to to work done and time taken, e.g. in electric stuff.
• Power (watts) = Energy (J) / time(s)

 

Energy

• • Units: Energy and work in joules but power in watts.
  • An object may have energy due to its motion (kinetic) or its position (potential), and that energy may be transferred and stored.
    • Because GCSE is what it is, always set ½ mv^2 = mgh

 

• Kinetic energy: Ek = ½ * mass (kg) * velocity(m/s)2

• Gravitational potential energy: U = mass (kg) * gravity (N/kg) * height (m)

 

• • Forms of energy: kinetic (object in motion), gravitational(object at height), chemical(batteries, food), strain(spring), nuclear(nuclear bombs), thermal (heat)(light and heat), electrical (in a circuit), light(bulbs and stars) and sound (loudspeaker).
  • Energy can be converted. E.g. Food can be converted to motion, electricity to light and sound.
  • Energy can be transferred. E.g. Light dissipates into surroundings, etc.

 

• Energy cannot be created nor destroyed. Always transferred/energy lost is dissipated into surroundings and others.

 

 

P2 Equations

 

• Kinetic energy: Ek = ½ * mass (kg) * velocity(m/s)2

• Gravitational potential energy: U = mass (kg) * gravity (N/kg) * height (m)

• Power from energy: Power (watts) = Energy (J) / time(s)

 

Work: Work done (N/J) = Force (N) * distance (m)

P1 Force and Motion

P1 Force and Motion

Distance, speed, time

Distance = time * speed

Average speed = total distance / total time

Velocity = speed + direction (vector, whereas speed is scalar)

Acceleration = speed / time

Qualitative understanding: acceleration is the rate of change of velocity per unit of time; the amount of speed changed in a second.

 

Mass and weight

• Mass is the quantity of matter which a body contains, as measured by its acceleration under a given force or by the force exerted on it by a gravitational field – mass resists change in motion.
• Weight = mass * gravity.
• Earth is a source of a gravitational field.

 

Effects of forces

• Force’s unit is newtons (N)
• Forces can change the size (compressions), shape (Stretch) and motion (acceleration) of a body.
• Opposite forces cancel and if they are in equilibrium, the forces are balanced in the system and there is no resultant force.

 

Hooke’s Law

• force = constant × extension (F = kx)
• This direct proportionality will reach a limit whereby the equation no longer applies and the spring reaches maximum extension.

 

P1 Equations

• • Acceleration/Speed with Object: Force = mass * acceleration

 

• Acceleration: speed/time

• Speed: Distance = time * speed

 

• • Pressure: Pressure = force / area (make sure you count how many foots of animal, etc.)
  • Springs: force = constant × extension (F = kx)

 

• Weight: Weight = mass * gravity.