C2 - Chemical resources

Lithosphere: outer layer of Earth, relatively cold and rigid - made out of tectonic plates that are less dense than the mantle 

• mantle - between core and crust, below the crust it's cold and rigid but is able to move at greater depths
• Earth's core transfers energy so temperature of mantle increases with depth
• convection currents slowly move plates
• oceanic crust is denser than continental crust - when they collide, oceanic plate sinks, pulls the plate down and partly melts = subduction

Rocks in lava:

• iron rich basalt rock comes from runny lava in slower volcanic eruptions
• silica-rich rock comes from thick lava in explosive eruptions

Raw materials:

• Clay --> brick, limestone and clay --> cement, sand --> glass, iron ore --> iron, aluminium ore --> aluminium

Limestone - sedimentary rock, made from soft sediments compressed together and cemented together, soft.

Marble - metamorphic rock, limestone changes by heat pressure, has interlocking mosaic of carbonate crystals, harder than limestone

Granite - igneous rock with interlocking crystals, formed when magma cools and solidifies, very hard

Thermal decomposition of cacium carbonate (limestone):

• CaCO₃ → CaO + CO₂
• calcium carbonate --> calcium oxide + carbon dioxide

Reinforced concrete:

• concrete is strong under compression but weak under tension
• heavy loads means the concrete will bend and create tension and compression - cracks
• reinforced concrete with steel rods stops the concrete from stretching and cracking

Purifying impure copper:

• advantages:
  • reduces need for mining, saving reserves and environmental problems caused by mining
  • keeps cost os copper down
• disadvantages:
  • actual seperating process may cause pollution
  • less copper mined so les mining jobs
• process of purification:
  • impure copper is anode, positive anode loses mass as copper dissolves
  • pure copper is cathode, negative cathode gains mass as pure copper plated onto it
• concentration of copper(II) sulfate solution stays the same because as impure copper anode dissolves, pure copper plated on cathode at same rate

At the anode:

• Cu atoms lose electrons to form Cu2+ ions - oxidation
  • Cu – 2e^- --> Cu²⁺

At the cathode:

• Cu2+ ions gain electrons to form Cu atoms - reduction

  • Cu²⁺ + 2e^- --> Cu

Alloys: mixtures conatining at least one metal

• amalgam - contains mercury, brass - contains copper and zinc, solder - contains lead and tin
• smart alloys: return to their original shape after being heated at a certain temperature
  • nitinol for spectacle frames return to its original shaper after being if put in hot water

Rusting is an oxidation reaction because iron reacts with oxygen and water to form an oxide:

• iron + oxygen + water ---> hydrated iron(III) oxide

Aluminium:

• lighter and more resistant to corrosion than steel
• fuel economy is improved

Steel - costs less and is stronger

Advantages of recycling materials from old cars:

• less mining saving finite resources, less crude oil for making plastics, less waste+landfill

Disadvantages:

• fewer mines built, difficult to seperate different materials, seperating techniques produce pollution, recycling processes are expensive

Haber process produces ammonia:

• word equation: nitrogen + hydrogen  ammonia
• symbol equation: N₂(g)       + 3H₂(g)  2NH₃(g)

Optimum conditions:

• iron catalyst - increases rate of reaction
• 450 degrees - increases reaction rate, breaks down ammonia which reduces % yield
  • yield is not very high but rate is fairly quick = best compromise
• high pressure of 200 atmospheres - increases % yield

What affects cost of chemical manufacture:

• reaction rate and % yield mist be high enough to give sufficient daily yield
• low % yield accepted if reaction can be repeated with recycled starting materials
• optimum condition give lowest cost not fastest rate and highest yields

Neutralisation - when acid and base react to make salt and water:

• acid + base ---> salt + water
• acids contain H+ ions - pH = concentration of H+ ions, the higher the concentration the lower the pH
• neutralisation - leaves no free H+ ions
• alkalis contain OH- ions
• neutralisation = H⁺ + OH^- → H₂O

Salts:

• acid + base --> salt + water OR acid + metal carbonate --> salt + water + carbon dioxide
• e.g. hydrochloric acid + copper carbonate --> copper chloride + water + carbon dioxide

  • 2HCl + CuCO₃ --> CuCl₂ + H₂O + CO₂

Growing crops:

• fertilisers must be dissolved in water because only dissolved substances are small enough to be absorbed by plants
• fertilisers are needed because the world population is rising and there is greater demand for food production
• they increase crop yield by:
  • replacing essential elements used by previous crops / providing extra elements
  • providing nitrogen that is incorporated into plant proteins resulting in increased growth

Eutrophication:

• fertilisers that wash off into waters increase nitrate and phosphate levels of water
• algae grow quickly on surface in presence of these (algal bloom) and block off sunlight to other plants which die
• aerobic bacteria use up oxgen i water and feed on dead and decaying plants and result in most organisms dying

Preparing fertilisers:

• made by reacting acid and alkali to make salt and water
• alkali is titrated with acid using indicator to find out quantities needed before main batch is made
• acid and alkali are now reacted completely to produce a neutral solution but are contaminated with indicator solution
• titration results are used to repeat experiement using correct quantities
• dissolved fertiliser is heated to evaporate most water, then left for remaining solution to crystallise and be filtered off

Electrolysis of sodium chloride solution:

• hydrogen made at cathode - Na+ and H+ ions migrate to negative cathode
  • electrons are gained = reduction --------> 2H⁺ + 2e^- --> H₂
• chlorine made at the anode - Cl- and OH- ions migrate to positive anode
  • electrons are lost = oxidation ----------> 2Cl^- - 2e^- --> Cl₂
• hydrogen and chlorine are reactive so its important to use inert electrodes so that products don't react before they are collected
• ions not discharged make sodium hydroxide solution

  • Na⁺ + OH^- --> NaOH