Agriculture and Industry (AI) notes from Storylines

These are my notes on AI from the Chemical Storylines textbook (not the Chemical Ideas textbook)
Please do check the specification (on the OCR website) for what you need to know exactly, these are just my personal notes

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  • Created on: 02-04-13 21:01
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02/04/13 E. Singh
Agriculture and Industry: Chemical Storylines notes
AI 1
The rapid increase in the human population means we must find ways to
produce more food to feed ourselves
Sustainable agriculture - increasing food production without degrading the
There are things we should be aware of and not do in order to keep sustainable
systems. For example, we know now that growing one crop again and again on
the same soil destroys its fertility by depleting specific nutrients
Land is not just 'farmed' for food. Forests are used for timber and oil seed rape is
used to make biofuels
AI 2
Organic chemistry - the study of compounds of carbon, excluding CO2, CO and
the carbonates which are studied in inorganic chemistry
Organic farming - a farming method mostly using fertilisers and pesticides of
only plant/animal origin (there is restricted use of artificial ones), with an
emphasis on soil health maintained through crop rotation and applying manure
and compost. Production of organic food follows a strict set of rules (AI 3, AI 4)
Soil - the thin layer on the top of the Earth's crust, made of mineral matter,
organic matter, soil solution and air. Weathering (the action of wind, rain, frost
and sunlight) makes soil out of the uppermost layers of weathered rock
Soil organic matter - consists of the products of decomposition; plant debris,
animal remains and excreta
Humus - organic component of soil, formed by the decomposition of leaves and
other plant material by soil micro-organisms. Carboxylic acid and phenol groups
are common in humus, both of which can lose H+ ions, leaving negatively
charged ions which can ionically bond to metal cations - humus can hold a
variety of nutrient ions like clays can
Keeping soil fertile - nutrient cycling
The nutrients plants need come from two places; an inorganic store in the
soil and an organic store partly on top and in the soil.
The organic store is replenished by organic manure, animal faeces and by
the death and decay of living organisms. Micro-organisms convert it into
inorganic ions by mineralisation producing ammonium, nitrate, nitrate(V),
phosphate and sulfate(VI) ions
Weathering of soil and rock minerals releases more ions into the inorganic
Nutrients can be lost by leaching out of the soil top layers by rainwater
Nitrogen (and other gases) can be lost by conversion into gases e.g. NH3, N2
and N2O which disperse into the atmosphere
The nitrogen cycle
Most of the nitrogen in the soil is not readily available to plants because it is
present in complex organic compounds

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E. Singh
Addition to soil nitrogen
Biological fixation - some bacteria in soil and in legume root nodules convert
nitrogen gas to NH4+ ions.
N2(g) = 8H+(aq) + 6e- 2NH4+(aq)
Other additions - lightning (splits NN) and burning hydrocarbon fuels
produce nitrogen oxides. These are released into the atmosphere and
deposited on the soil
Transformations in the soil
Mineralisation - when soil bacteria and other micro-organisms break down
organic nitrogen compounds into simpler molecules and ions.…read more

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E. Singh
In the Haber process, the following reaction takes places:
N2(g) + 3H2(g) 2NH3(g)
For this process, a high pressure gives a greater yield of ammonia, however the
higher the pressure, the greater the cost and maintenance of equipment
needed e.g. strong reaction vessels.…read more

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E. Singh
Pyrethroids are compounds related to ntural pyrethrins - active against insects
but do not oxidise in light
In mammals, pyrethroids are rapidly broken down into polar products by
oxidation or hydrolysis of the ester group present, then excreted
Synthetic pyrethroids persist on crops for 7-30 days.…read more

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