C2 - chemical resources Flashcards
What is the lithosphere?
The outer layer of the earths crust.
What does the lithosphere comprise of?
The lithosphere is relatively cold and rigid and compromises the crust and top part of the mantle.
How is information about earth collected and why in this way?
The crust is too thick to drill through, so most of our information about the earth is collected from seismic waves produced by earthquakes and man-made explosions.
What is the mantle and its properties?
The mantle is the zone between the core and the crust. It is cold and rigid just below the crust, but at greater depths it is hot and non-rigid and able to move.
Why does the temperature of the mantle increase with depth?
Because the earth’s core transfers energy.
What moves the earths plates slowly?
Convection currents.
What is subduction?
Oceanic crust is denser than continental crust. When these plates collide, the oceanic plate (which is called at the margins) sinks, pulling more of the plate down, and partly melting as it reaches the hotter part of the mantle.
What is plate tectonic theory?
Plate tectonic theory suggests that Africa and South America could once have been one land mass.
What is the evidence for plate tectonic theory?
It explains a wide range of evidence.
It has been discussed and tested by many scientists.
In the 1960s, new sea floor spreading evidence was found. Subsequent research led to Wegener’s theory slowly becoming accepted.
What does magma rise up through the earth’s crust?
Because it is less dense than the crust.
What are the properties of iron-rich basalt rock?
Iron-rich basalt rock comes from runny lava in slower volcanic eruptions.
What are the properties of silica-rich rhyolite rock?
Silica-rich rhyolite rock comes from thick lava in explosive eruptions.
How can hardness of materials be compared?
By rubbing them together.
Why is limestone soft?
Limestone is a sedimentary rock. It is made from soft sediments compressed and cemented together. This makes limestone quite soft.
Why is marble harder than limestone?
Marble is a metamorphic rock formed when limestone is changed by heat and pressure, and is typically composed of an interlocking mosaic of carbonate crystals. Marble is harder than limestone because it has been baked.
Why is granite very hard?
Granite is formed when magma cools and solidifies. It is an igneous rock with interlocking crystals. This makes it very hard.
What is thermal decomposition?
Thermal decomposition is a reaction where one substance breaks down on heating to give at least two new substances.
What is the thermal decomposition of limestone (calcium carbonate)?
Calcium carbonate –> calcium oxide + carbon dioxide
CaCOthree –> CaO + COtwo
How is cement made?
Cement is made when limestone is heated with clay.
How is concrete made?
Concrete is made by mixing cement, sand and small stones with water.
What is a composite material?
Composites contain at least two materials which can be distinguished. e.g reinforced concrete
Why is reinforced concrete a better construction material then concrete?
- concrete is strong under compression but weak under tension
- if heavy loads are applied to a beam, the concrete will bend. This creates tension and compression. The tension cracks the concrete
- reinforced concrete is harder and more flexible than concrete, so is a better construction material
What are the advantages of recycling copper?
- it has a fairly low melting point so the energy cost to melt is low
- it reduces the need for mining, saving reserves and the environmental problems caused by mining
- it keeps the cost of copper down
What are the disadvantages of recycling copper?
- the 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 there are fewer mining jobs
- the actual separating process may produce pollution
- a lot of copper is thrown away as it is difficult to persuade people to recycle it
What solution is used in the purification of copper by electrolysis?
An electrolyte of copper(II) sulfate solution is used.
Why occurs at the anode in the electrolysis of copper?
The positive anode loses mass as the copper dissolves.
Why occurs at the cathode in the electrolysis of copper?
The negative cathode gains mass as pure copper is played into it.
Why does the concentration of the copper(II) sulfate electrolyte stay the same during electrolysis?
Because as the impure copper anode dissolves, pure copper is played on to the cathode at the same rate.
What electron half equation happens at the anode during copper purification?
Cu - 2e(little minus) –> Cu(two plus)
What electron half equation happens at the cathode during copper purification?
Cu(two plus) + 2e(little minus) –> Cu
What is oxidation and reduction?
Oxidation - loss of electrons
Reduction - gain of electrons
What’s an alloy?
Alloys are mixture containing at least one metal.
What do different alloys contain?
- amalgam, contains mercury (this is used for filling teeth)
- brass, contains copper and zinc
- solder, contains lead and tin
What is nitinol (nickel titanium)?
It’s a smart alloy which is used to make spectacle frames; it returns to its original shape after being bent if it is put in hot water.
Smart alloys are becoming more important as new ways to use them are found.
What’s a smart alloy?
They return to their original shape after being heated to a certain temperature.
What accelerates rusting?
Acid rain and salt water.
What is the word equation for rusting?
iron + oxygen + water –> hydrated iron(III) oxide
This is an oxidation reaction be use iron reacts with oxygen forming an oxide.
Why doesn’t aluminium corrode in moist air?
Because it has a protective layer of aluminium oxide, which, unlike rust, does not flake off the surface.
Steel is harder and stronger than iron and steel is less likely to corrode than iron. True of false?
True.
What’re the advantages and disadvantages of aluminium car bodies compared to steel car bodies?
Aluminium is lighter and more resistant to corrosion than steel. However, steel costs less and is stronger.
A lighter aluminium body means fuel economy is improved. Because aluminium corrodes slowly, the car will also last long.
What is the word equation for the haber process?
Nitrogen + hydrogen ammonia
What is the balanced symbol equation for the haber process?
Ntwo + 3Htwo 2NHthree
What are the optimum conditions for the haber process?
- use a catalyst made of iron
- raise the temperature to about 450•C
- use high pressure (about 200 atmospheres/20 MPa)
- recycle any unreacted nitrogen and hydrogen
Why are these the optimum conditions for the haber process?
- the iron catalysts increase the ROR but not the PY
- high pressure increases the PY of ammonia
- a high temperature increases reaction rate
- a high temperature breaks down ammonia, reducing PY
-the optimum temperate is around 450•C. Although the yield is not very high, the rate is fairly quick. This is the best compromise.
What increases costs of chemical manufacture?
When the pressure is raised (increasing the plant costs) and the temperature is raised (increasing the energy costs).
What decreases costs of chemical manufacture?
When catalysts are used, unreacted starting materials are recycled and automation is used (reducing wage bills).
What considerations determine the conditions used to manufacture a chemical?
Both the reaction rate and percentage yield need to be high enough to give a sufficient daily yield of product
A low percentage yield can be accepted if the reaction can be repeated many times with recycled starting materials
Optimum conditions give the lowest cost
What is the word equations for making salt?
Acid + base –> salt + water
Acid + metal carbonate –> salt + water + carbon dioxide
Why do fertilisers need to be soluble?
So they can be absorbed by plants roots as only dissolved substances are small enough to be absorbed
How do fertilises increase crop yield?
Replacing essential elements used by the previous crop providing extra essential elements and providing nitrogen that is incorporated into plant protein resulting in increased growth
What is eutrophication?
Eutrophication is when:
- Fertilises are washed off fields
- Fertiliser in the water increase the nitrogen and phosphate levels in ponds lakes and rivers
- These chemicals cause algal bloom
- Aerobic bacteria use up all the oxygen in the water and feed on the dead and decaying plants
- Most living organisms die
-excessive use of fertilisers can also pollute water supplies
In what to ways is salt mined in Cheshire?
Mining from the ground as rocksalt and solution mining by pumping in water and extracting saturated salt solution.
Mining can lead to subsidence. What is subsidence?
The ground above a mine can sink causing landslips and dear prying homes. Salt at the surface, particularly brine solution, can escape and effect habitats.
What are the election half equations at the cathode and anode during the electrolysis of brine?
At the cathode, hydrogen is made, electrons are gained so this is reduction:
2H+ + 2e- –> Htwo
At the anode chlorine is made, electrons are lost so this is oxidation:
2Cl- – 2e- –> Cltwo
The ions not discharged make sodium hydroxide solution:
Na+ + OH- –> NaOH
How is sodium chloride solution separated?
By electrolysis.
Hydrogen is made at the negative cathode.
Chlorine is made at the positive anode.
Sodium hydroxide forms in solution.
Hydrogen and chlorine are reactive so it is important to use inert electrodes so that the products for react before they are collected an the electrodes do not dissolve.
What are sodium hydroxide and chlorine involved in making?
Household bleach, chemicals, solvents, plastics, paints, soaps, medicines and food additives.
How do you produce a fertiliser from the reaction of an acid and an alkali?
The alkali is titrated with the acid using an indicator to find out the quantities needed before the main batch is made (this is repeated until the results are consistent)
Although the acid and alkali have now reacted completely to produce a neutral solution of ammonium sulfate fertiliser, this is contaminated with indicator solution
The titration results are used to repeat the experiment using the correct quantities
The dissolved fertiliser is heated to evaporate most of the water off, then left for the remaining solution to crystallise. The crystals are then filtered off.
