C3- Chemicals In Our Lives Flashcards
What are tectonic plates?
The crust and upper part of the mantle are cracked into a number of large pieces called tectonic plates.
Most plates move at speeds of a few cm per year.
How do magnetic clue in the rock show movement of tectonic plates?
When tectonic plates move away from each other, under the sea the exposed mantle rises up through the seafloor and solidifies to from a new crust.
When the crust is formed its magnetised by the earths magnetic field. Every half million years or so the Earths magnetic field swaps direction. So the rocks either have normal polarity or reversed polarity when they cool.
The pattern of normal and reversed polarised rocks can be used to estimate the age of different parts of the earths crust. And track the slow movement of tectonic plates.
How do rocks contain clues of the earths history?
Fossils- These are the remains or imprints of dead organisms. They tell you about the age of the rock. And also the conditions it was formed in.
Rocks formed underwater- Contain shells and ripples on it created by the sea or rivers.
The sediment- That forms the rocks will either have been carried by water or air. By looking at the shape of the grains you can tell if the rock was formed underwater or on the surface.
Why does the earths crust contain minerals?
Different types of rock in the sets surface contains different minerals.
The minerals are formed by; sedimentation, dissolving, evaporation, erosion, and mountain building.
Chemical industries tend to grow up where useful mineral resources can be found nearby.
How is limestone formed?
Limestone is a sedimentary rock which contains calcium carbonate. They are formed in layers of sediment in the bottom of lakes and rivers.
The sediment comes from shells and bones of sea creatures and the erosion of existing rocks.
Erosion is natural weathering in which large pieces of rock by the rain and wind. This causes tiny particles of sediment to get washed away in the bottom of lakes.
Millions of layers of sediment get buried and the weight of the sediment on top of them squeezes the water out.
Fluids flowing through pores in the sediment deposit natural mineral cement that holds the sediment particles together to form a rocks.
What is coal?
It is formed over millions of years of fossilisation of layers of plant matter. It consists of carbon.
They are formed when coal deposits are put under high pressures and temperatures.
Salt left by evaporation?
In Britain, salt is extracted from underground deposits.
These underground deposits were formed when ancient seas containing dissolved salt evaporated. The salt that was left behind was buried and compressed by other layers of sediment for over millions of years.
There are massive deposits of this rock salt under Cheshire and Teeside.
Normal salt mining?
- Rock salt is drilled, blasted and dug out and brought to the surface using machinery.
- Most rock salt obtained brought this type of mining is used on roads to stop ice forming.
- The salt can be separated out and used to enhance the flavour in food. Or for making chemicals.
Solution mining?
- In solution mining water is injected into the salt deposit through the outer pipe.
- Which dissolves the salt to make a saltwater named brine.
- Pressure forces the brine up to the surface through the inner pipe.
- The brine is then stored in wells above the surface. And pumped to a refining plant when it’s needed.
- Impurities are removed from the brine in the refining plant. Then it’s pumped into containers. The brine is then boiled to make the water evaporate- leaving the salt behind.
- Table salt and salt for chemical production are made this way.
Impacts on environment from mining?
• Land above disused mines can collapse into holes- subsidence.
This affects buildings and homes.
- The risk of subsidence is reduced by leaving well supported caverns in mines. Caverns can be spaced well apart, and filled in when no longer needed.
- Mining needs a lot of energy. Which comes from burning fossil fuels this uses up finite resources and pollution.
Salt from the sea?
In hot countries, like Australia and China salt can be obtained by evaporating seawater.
Seawater flows into specially built shallow pools. And left to evaporate in the sun-leaving the salt behind.
This process is repeated and the salt is collected. This method produces the purest salt- it can be 100% sodium chloride.
Uses of salt in food production?
- Refined salt added to processed foods to enhance the flavour.
- Used as a preservative- longer life.
Health issues from salt?
- Too much salt- high blood pressure- strokes- heart attacks.
- Too much salt- increases chance of stomach cancer, osteoporosis and renal failure.
Government guidelines on salt?
- Included maximum guideline daily amounts (GDA) of how much salt people should have per day, depending on age.
- The department of health have to do two things;
- risk assessments for chemicals in foods to make sure their safe.
- Advise the public about how salt affects health.
• However, food manufacturers may not change their salt in products. As the cost to reforms late ingredients is too great. Also if they add less salt to a product it may not taste as good. This less products are sold.
Salt in the chemical industry?
Salt is important to the chemical industry.
They electrolyse the salt solution (brine), this involves passing electric currents through it.
Electrolysis causes chemical change- it splits the solution into hydrogen, chlorine and sodium hydroxide.
