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.

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.