C2- Chemical Resources Flashcards
What is the outer layer of the Earth called?
Lithosphere
What is the lithosphere composed of?
Crust and upper mantle
Relatively cold and rigid layer
What is the lithosphere made up of?
Tectonic plates, which are less dense than the mantle below
Where is most information about the Earth from?
Seismic waves produced by earthquakes and man-made explosions (as the crust is too thick to drill through)
What state is the mantle in?
Cold and rigid just below the crust, but at greater depths it is hot and non-rigid and able to move
What temperature is the mantle?
Increases at depths due to the Earth’s core transferring energy
What moves the plates?
Convection currents
What is subduction?
- oceanic crust is denser than continental crust
- when plates collide, oceanic plate (cooler at the margins) sinks
- pulls plate down and oceanic plate melts as it reaches the hotter part of the mantle
Why do scientists now accept the theory of plate tectonics?
- it explains a wide range of evidence
- has been discussed and tested by many scientists
What was Wegener’s continental drift theory and why has it now been accepted?
His idea was that the Earth’s continents were once joined together, but gradually moved apart over millions of years. In 1960s, new sea floor spreading evidence was found and is now accepted.
What evidence was there for the continental drift theory?
- same types of fossilised animals and plants are found in South America and Africa
- shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle
- matching rock formations and mountain chains are found in South America and Africa
Why does magma rise through the Earth’s crust?
It is less dense than the crust and can cause volcanoes
Why do geologists study volcanoes?
- to try to forecast future eruptions
- reveal more about the structure of the Earth
Which raw materials make which building materials?
- clay ⇒ brick
- limestone and clay ⇒ cement
- sand ⇒ glass
- iron ore ⇒ iron
- aluminium ore ⇒ aluminium
What type of rock is limestone?
Sedimentary rock
What is sedimentary rock?
Rock which has formed when fragments of older rock or living things have stuck together or by precipitation
Is limestone hard?
It is quite soft as it was made from soft sediments compressed and cemented together
What type of rock is marble?
Metamorphic rock
What is metamorphic rock?
Rock which has been changed after it has formed
Is marble hard?
Marble is harder than limestone as it has been changed by heat and pressure, composed of interlocking mosaic of carbonate crystals
What type of rock is granite?
Igneous rock
What is igneous rock?
Rock which has formed when liquid rock has solidified
Is granite hard?
It is very hard as it was formed when magma cools and solidifies, made with interlocking crystals.
What is thermal decomposition?
A reaction when one substance breaks down on heating to give at least two new substances
What is the equation for the thermal decomposition of limestone?
calcium carbonate → calcium oxide + carbon dioxide
CaCO3 → CaO + CO2
How is cement made?
When limestone is heated with clay
How is concrete made?
Mixing cement, sand and small stones with water
What is reinforced concrete?
A composite material which has steel rods or meshes running through it. Composites contain at least two materials that can still be distinguished
When is concrete strong and weak?
Strong under compression (squashing) but weak under tension (pulling)
What happens when heavy loads are applied to a concrete beam?
The concrete bends, creating tension and compression. The tension crack the concrete
Why is reinforced concrete better than concrete?
It is harder and more flexible
How can impure copper be purified?
Electrolysis
What are the advantages of recycling copper?
- low melting point so energy cost to melt it is low
- reduces the need for mining, saving reserves and environmental problems caused by mining
- keeps costs of copper down
What are the disadvantages and problems of recycling copper?
- small amounts used in electrical equipment are difficult to separate
- valuable ‘pure’ copper scrap must not be mixed with less pure scrap, such as solder
- less copper is mined so fewer mining jobs
- separating process may produce pollution
- lots of copper thrown away as it is difficult to persuade people to recycle it
What electrolyte is used in the purification of copper by electrolysis?
copper (II) sulfate solution
What happens during the electrolysis of copper?
- positive anode loses mass as the copper dissolves
- negative cathode gains mass as pure copper is plated onto it
Which is the anode and which is the cathode?
- Impure coper is the anode
- sheet of pure copper is used for the cathode
What happens to the concentration of copper(II) sulfate electrolyte?
Stays the same as the impure copper dissolves, pure copper is plated on to the cathode at the same rate
What happens at the anode?
Cu atoms lose electrons to form Cu2+ ions
OXIDATION
What is the electron half equation for the anode?
Cu - 2e- → Cu2+
What happens at the cathode?
Copper is plated when Cu2+ ions gain electrons
REDUCTION
What is the electron half equation for the cathode?
Cu2+ + 2e- → Cu
What are alloys?
Mixtures containing at least one metal
What is amalgam made of and used for?
Contains mercury and used for filling teeth
What is brass made of?
Copper and zinc
What is solder made of?
Lead and tin
What is a smart alloy?
An alloy which will return to its previous shape after being heated to a certain temperature
What is nitinol made of and used for?
Nickel-titanium and used to make spectacle frames
Which metals rust?
Iron and steel only
What can accelerate rusting?
Acid rain and salt water
What type of reaction is rusting?
Oxidation because iron reacts with oxygen forming an oxide
What is the word equation for rusting?
iron + oxygen + water → hydrated iron(III) oxide
Why does aluminium not corrode in moist air?
It has a protective layer of almunium oxide which unlike rust, does not flake off the surface
Why would these materials be used in cars?
- aluminium in car bodies and wheel hubs
- iron / steel in car bodies
- copper in electrical wires
- lead in lead-acid batteries
- plastic in dashboards, dials and bumpers
- pvs in metal wire coverings
- glass and plastic/glass composite in windscreens
- fibre in seats
- does not corrode, low density, malleable, quite strong
- malleable, strong
- ductile, good electrical conductor
- chemical reaction with lead oxide produces electricity
- rigid, does not corrode, cheap
- flexible, does not react with water, electrical insulator
- transparent, shatterproof
- can be woven into textiles, can be dyed, hard-wearing
What is an alloy?
Mixtures of elements containing at least one metal and often have different and more useful properties than the metals they are made from
What are examples of alloys?
Steel (iron and carbon) is harder and stronger than iron and less likely to corrode than iron
What are the advantages of steel or aluminium for car bodies?
Aluminium is lighter and more resistant to corrosion than steel.
Steel costs less and is stronger
What are the advantages of recycling materials from old cars?
- less mining saves finite resources needed to make metals
- less crude oil is needed to make new plastics
- less waste means less landfill
- fewer toxic materials, such as lead from batteries, are sumped
What are the disadvantages of recycling materials from old cars?
- fewer mines are built and fewer mining jobs
- difficult to separate the different materials
- some separating techniques produce pollution
- some recycling processes are expensive
What process make ammonia?
The Haber process
What is the word equation for the Haber process equation?
nitrogen + hydrogen ⇔ ammonia
What is the balanced symbol equation for the Haber process?
N2 + 3H2 ⇔ 2NH3
What are the optimum conditions for the Haber process?
- iron catalyst
- temperature of about 450ºC (fairly low for an industrial process)
- high pressure (about 200 atm)
- recycle any unreacted nitrogen and hydrogen
How is the Haber process conditions efficient?
- catalyst increases reaction rate (rate of successful collisions) but not the percentage yield
- high pressure increases reaction rate
- high temperature breaks down ammonia, reducing percentage yield
- optimum temperature is the best compromise of a reasonable yield and fast rate
What increases costs of chemical manufacture?
When pressure is raised (increasing plant costs) and the temperature is raised (increasing energy costs)
What decreases costs of chemical manufacture?
When catalysts are used, unreacted starting materials are recycled and automation is used (reduces wage bills)
How do the economic considerations determine the conditions used to manufacture a chemical?
- both reaction rate and percentage yield must be high enough to give sufficient daily yield
- low percentage yield can be accepted if reaction can be repeated many times with recycled starting materials
- optimum conditions give lowest cost, rather than faster rate or highest yields
What is a base?
Substance that will react with acids
Name exaples of bases
Metal oxides and metal hydroxides
What are alkalis?
Substance which produce OH- ions in water. Bases that are soluble in water e.g. sodium hydroxide
What is neutralisation?
When an acid and a base reacts to make salt and water
What is the word equation for neutralisation?
acid + base → salt + water
What does universal indicator show?
A gradual range of colour changes, as it contains a mixture of different indicators
What do all acids contain?
H+ ions (hydrogen ions)
What is the pH of acid determined by?
The concentration of H+ ions. The higher the concentration, the lower the pH. Neutralisation leaves no free hydrogen ions
What is the symbol equation for a reaction that involves neutralisation?
H+ + OH- ⇔ H2O
What do acids react with?
Acids react with bases and metal carbonates to form salts
What are the word equations for making salts?
acid + base → salt + water
acid + metal carbonate → salt + water + carbon dioxide
What would these acids be called as a second part of the salt name?
- Sulfuric acid
- Nitric acid
- Hydrochloric acid
- Phosphoric acid
- Sulfate
- Nitrate
- Chloride
- Phosphate
What is the word equation for the reaction between hydrochloric acid and copper carbonate?
Hydrochloric acid + copper carbonate → copper chloride + water + carbon dioxide
What is the symbol equation for the reaction between hydrochloric acid and copper carbonate?
2HCl + CuCO3 → CuCl2 + H2O + CO2
Why do farmers use fertilisers?
To increase their crop yields
What must the fertilisers be so the plants can absorb them?
Fertilisers must be dissolved in water as only dissolved substances are small enough to be absorbed by plant roots
Why are fertilisers needed?
The world population is rising and there is a greater demand for food production from the land available
How do fertilisers increase crop yield?
- replacing essential elements used by the previous crop or providing extra essential elements
- providing nitrogen that is incorporated into plant protein resulting in increased growth
What happens when fertilisers go into ponds, lakes and rivers?
Leads to eutrophication
What happens during eutrophication?
What is the process of producing a fertiliser from a reaction of acid and alkali?
- alkali is titrated with the acid using an indicator to find out the quantities needed before main batch is made (repeated until results are concurrent)
- although acid and alkali have now reacted completely to produce a neutral solution of ammonium sulfate fertiliser, this is contaminated with indicator
- titration results used to repeat experiment with correct quantities
- dissolved fertiliser is heated to evaporate most of the water, then left for the remaining solution to crystallise
- crystals filtered off
What are the two ways to mine salt in Cheshire?
- mining in ground as rock salt
- solution mining by pumping in water and extracting saturated salt solution
What can salt mining lead to?
Subsidence when the ground above a mine can sink causing landslips and destroying homes
What can salt at the surface (especially brine solution) do?
Escape and affect habitats
How can concentrated sodium chloride solution (brine) be separated?
By electrolysis
What occurs during electrolysis of brine?
- hydrogen is made at the negative cathode
- chlorine is made at the positive anode
- sodium hydroxide forms in solution
What must be done to prevent hydrogen and chlorine from reacting during electrolysis of brine?
To use inert electrodes so that the products don’t react before they are collected and the electrodes do not dissolve
What occurs during the electrolysis of NaCl solution?
- Na+ and H+ ions migrate to the negative cathode
- Cl- and OH- ions migrate to the positive anode
At cathode:
2H+ + 2e- → H2 (REDUCTION)
At anode:
2Cl- - 2e- → Cl2 (OXIDATION)
Ions not discharged make sodium hydroxide solution:
Na+ + OH- → NaOH
What can be used to make household bleach?
Sodium hydroxie and chlorine
Why are chlorine and sodium hydroxide important raw materials?
They are involved in making a lot of chemicals
e.g. solvents, plastics, paints, soaps, medicines and food additives
