Chemical monitoring and mangagement summary
9.4.2.1 identify and describe the industrial uses of ammonia
Ammonia is used to make solid and liquid fertilizers, explosives, nitric acid, sodium
carbonate and some pharmaceuticals and household cleaners,. It is also used as a
refridgerant.
To make solid fertilized industrially, ammonia which is a weak base is reacted with
sulfuric acid to form ammonium sulfate fertilizer and with nitric acid to form ammonium
nitrate fertilizer.
Identify that ammonia can be synthesized from its component gases nitrogen and
hydrogen.
Under pressure and heat nitrogen and hydrogen react in the ration of 3 volumes of
nitrogen to 1 volume of hydrogen to produce 2 volumes of ammonia
1 mol N + 3 mol H  2 mol NH3
Describe the synthesis of ammonia occurs as a reversible reaction that will reach
equilibrium
The synthesis of ammonia occurs as a reversible reaction. This means that ammonia is
formed for n and h and once some is produce the reverse reaction happens. When n and h
are initially added to the reaction vessel the reaction is slow. Equilibrium is reached whe
the rate of the forward reaction = rate of the reverse reaction.
To produce ammonia it needs to be shifted to the right
N2(g) + 3H2(g)  2NH3 (g)
Identify the reaction of hydrogen with nitrogen as exothermic
In the forward reaction to produce ammonia it release 46kj of energy per mol NH3
formed.
Explain why the rate of reaction is increased by higher temperatures
Higher temperatures will favour the left (endothermic) reaction make less ammonia but
are need because at lower temperatures equilibrium would take years to establish and be
impractical.
Explain why the yield of the product in the haber process is reduced at higher
temperatures
Higher temperatures would favour the reverse reaction by LCP because it is exothermic,
thus producing less NH3 and more of the reactants.
Explain why the haber process is base on a delicate balancing act involving reaction
energy, reaction rate and equilibrium.
As the temperature is increase more energy is available to exceed the reaction activation
energy and thus the reaction rate between n and h to for nh3 increases. However
increasing temperature favours decomposition of the ammonia product. A compromise
temp providing a satisfactory reaction rate and satisfactory yield of ammonia is selected.
9.4.3.1
Deduce the ions present In a sample from the results of tests
The two types of ions are Cations (positive, have lost 1 or more electrons), attracted to
cathode in electrolytic cell (electrolysis is reverse)
Anions (negative, gain 1 or more electrons) attracted to anode.
Ions are most commonly identified by precipitation reactions, however these may
sometimes identify trace amounts of the ions in question.
A flow chart is often used to eliminate the multiple ions in search for one.
9.4.3.2 Describe the use of atomic absorption spectroscopy (AAS) in detecting
concentrations of metal ions in solutions and assess it’s impact on scientific
understanding of the effects of trace elements.
AAS detects minute concentrations of an element in a sample solution by reading the
unique absorption spectrum, that is related to an elements electron energy levels.
The flame containing the atomized sample absorbs light at the particular wavelengths
characteristic to a particular elements in the flame and re emits in all directions. A
detector records the intensity of light at each wavelength and a sharp drop in the intensity
of a particular wavelength indicates the spectrum. The relative intensity and pattern of
changes in intensity within each of the bands in the absorption spectrum indicate the
concentration of the element in the test sample.
AAS has allowed for a great enhancement in the study of pollutants in the environment,
being a extremely accurate way of detecting trace elements in a substance.
Trace elements are needed in small amounts by living things and AAS has allowed many
deficiencies etc to be found in some environments.
9.4.4.1 Describe the composition and layered structure of the atmosphere.
The atmosphere is a 200-300km thick layer of gas surrounding the earth, with 75% of it’s
mass below 15km, 99.997% below 90km. comprises mainly of nitrogen (78%), oxygen
(21%) and argon (0.93%)
It consists of two main layers; the troposphere and the stratosphere.
Troposphere goes from the earths surface to 15km, the temperature drops with altitude in
the troposphere. At the top is a region where the temp is relatively stable (tropopause;
reduces the mixing of gases)
The stratosphere is above the tropopause, in this temperatures rise with increasing
altitude.
9.4.4.2 Identify the main pollutants found in the lower atmosphere and their
sources.
Main pollutants
Main sources
Carbon monoxide
Incomplete combustion in stoves, cars,
fires and cigarettes.
Nitrogen oxides
Combustion at high temperatures in
vehicles and power stations.
Volatile organic compounds, such as Solvents and unburnt fuels.
hydrocarbons
Sulfur dioxide
Some metal extraction processes and the
burning of fossil fuels
Lead
Leaded fuels, metal extraction, renovation
old house containing leaded paints and
electrical wire coverings
Particulates
Incomplete combustion, earthmoving dust
storms and some agricultural and industrial
practices
9.4.4.3 Describe ozone as a molecule able to act both as an upper atmosphere UV
radiation shield and a lower atmosphere pollutant.
Ozone is an allotrope of oxygen with the formula O3. It is naturally in very small
concentrations near the ground (0.02ppm) and is poisionous to humans and animal life,
also being extremely reactive and capable of oxidizing many substances, making it a
lower atmosphere pollutant. Large ozone concentrations make up photochemical smog.
In the upper atmosphere however it forms a very thin ozone layer which filters out short
wavelength UV light which is damaging to living tissue.
9.4.4.4 Describe the formation of a coordinate covalent bond.
A coordinate covalent bond is one in which both of the shared electrons came from the
one atom. In ozone, O2 is joined together normally and an unbonded pair of electrons
from one of the O atoms breaks off and is shared with another O atom. Although this
bond is produced differently it is still exactly the same.
9.4.4.5 Demonstrate the formation of coordinate covalent bonds using lewis electron
dot structures ^^^^^^^^^^^^
9.4.4.6 Compare the properties of oxygen allotropes O2 and O3 and account for
them on the basis of molecular structure and bonding.
Properties
Gaseous oxygen
Gaseous ozone
Explanation
Colour
Colourless
Blue
Boiling point
-183
-111
The boiling point of
diatomic oxygen is
lower than that of
the
ozone
as
diatomic oxygen has
Solubility in water
Sparingly soluble
More soluble than
oxygen
Chemical stability
Far more stable than Far less stable than
ozone
the
oxygen
molecule
Oxidation ability
Less
oxidant
powerful More
oxidant
powerful
lower
molecular
mass requiring less
energy in the boiling
process.
Non-polar O2 doesn
not form strong
intermolecular
forces in the polar
water. Ozone has a
bent
structure,
which provides for
some polarity of the
molecule in it’s
interaction
with
water
Ozone is easily
decomposed
into
oxygen molecules
2O3(g) 3O2(g)
e.g. reaction with
metals;
oxygen
forms the oxide as
the only product
whereas
ozone
reacts more readily
producing
the
metallic oxide and
an oxygen molecule.
9.4.4.7 Compare the properties of the gaseous forms of oxygen and the oxygen free
radical.
Oxygen in its ground state has three pairs of electrons. When O2 is broken up it creates
two oxygen free radicals each with two electron pairs and two unpaired electrons. The
energy abosorbed in splitting the diatomic oxygen makes it very reactive.
In order of reactivity O>O3>O2.
9.4.4.8 Identify the origins of chlorofluorocarbons (CFC’s) and halons in the
atmosphere.
CFC were developed in the 1930’s to replace ammonia as a refrigerant. This was due to
their properties being deemed safer than the explosive ammonia. Their inertness and low
boiling point allowed them to be used as solvents propellants and blowing agents
releasing the gases into the atmosphere.
It was discovered that CFC did not react even react in the troposphere and made their
way up to the stratosphere where uv energy broke the C-Cl bond and released Cl free
radicals. These then react with ozone to deplete the ozone layer.
Halons used In fire extinguishers underwent the same effect as CFC’s releasing even
more reactive bromine free radicals, fortunately they were not used as much.
9.4.4.9 Identify and name examples of isomers (excluding geometrical and optical) of
haloalkanes up to eight carbon atoms
9.4.4.10 Discuss the problems associated with the use of CFC’s and assess the
effectiveness of the steps taken to alleviate these problems.
CFC’s create problems of the depletion of the ozone layer, more UV radiation reaching
earth (causing cancer), and an increase in the enhanced greenhouse effect.
The can last for 150years depleting the ozone layer.
Steps to reduce the formation of an ozone hole are: the montreal protocol; a treaty for the
global reduction in CFCs, the identification and introduction of alternative chemicals
such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), assistance
to less developed countries to phase out CFC use.
Global cooperation is needed to effective implement these steps.
9.4.4.11 Analyse the information available that indicates changes in atmospheric
ozone concentrations, describe the changes observed and explain how this
information was obtained.
Changes in atmospheric ozone concentrations where first noticed in the late 1970’s over
the entire antartic. These measurements were take using UV spectrophotometers which
were directed vertically upwards into the atmosphere. These spectrophotometers could
also be directed vertically down and helium filled balloons used them.
Later satellites were used to carry a total ozone mapping spectrophotometer (TOMS)
which proved very efficient in recording changes in ozone levels.
9.4.5
9.4.5.1 Identify that water quality can be determined by considering;
- Concentrations of common ions
- Total dissolved solids
- Hardness
- Turbidity
- Acidity
- Dissolved oxygen and biochemical oxygen demand
AAS and gravimetric analysis are the most common way s of determining the
concentration of ions in the water are within world health standards.
Total dissolved solids (TDS)
TDS are determined by evaporation to dryness of a known volume of a filtered sample.
The value is converted to ppm and expressed in mass per volume units. If the solids are
ionic there amount can be determined by a conductivity probe and data logger.
Hardness
Hardness is due to the presence of calcium and magnesium ions in the water. These form
insoluble compounds with soap ions and produce scum stopping the soap from lathering.
Hardness is tested by precipitating the calcium and magnesium ions from a known
volume of water sample with a solution of sodium carbonate (of known concentration)
followed by filtering and drying of the precipitate. Most of the insoluble salt is assumed
to be calcium and the concentration of calcium ions is calculated and reported in ppm.
Acidity
A ph reading below 7 would be expected where there are acid sulfate soils or where there
is acid produced by decomposition of organic matter in stagnant situations. The test can
be conducted with a data logger and pH probe, universal indicator solution or paper or pH
meter.
Dissolved oxygen
There are several test for determining the DO in a water sample. The winkler method
fixes the amount of dissolved oxygen, which is later determined by titration.
The amount of manganese dioxide produce by adding manganese (II) ions and hydroxide
ions is a measure of DO. Acified iodide ions are added to cause the manganese dioxide to
produce a yellow iodine solution. This is then titrated against a standard sodium
thiosulfate solution using starch as the indicator. The indicator turns a blus colour with
the iodine and the blue disappears at the endpoint. To conduct the test no aid is to be
trapped with the sample and it is to be kept in the dark to reduce algae photosynthesis
increasing the DO.
Biochemical oxygen demand (BOD)
BOD measures the amount of oxygen used by bacteria and other micro-organisms during
a five-day period. The sample bottles are held below the water surface and away from the
bank. One sample is measured for DO as soon as possible while the other sample is kept
in a dark place for 5 days then tested for DO. The difference between the two is the
reading give as milligrams per litre.
9.4.5.2 Identify factors that affect the concentration of a range of ions in solution in
natural bodies of water such as rivers and oceans.
Factors include:
- The frequency of the rainfull (i.e. floods and droughts)
- Water temperatures
- Evaporation rates
- Soil type
- Pollution sources, such as the presence of animal faeces and gertiliser usage
(leading to eutrophication)
- Land use
Removal of vegetation due to farming and development practice increase the amount of
salt in the water table an thus in the rivers.
Earthmoving on waterside developments can expose layers containing sulfide to air,
oxidizing them and producing sulfuric acid which can kill fish etc.
High evaporation rate sin the dead sea have increased salt concentration
Run off water containing phosphate and other ions, affecting the growth of organisms.
9.4.5.3 Describe and assess the effectiveness of methods used to purify and sanitise
mass water supplies.
Most purification methods are variations of the following process
Flocculation and sedimentation filtration  sanitization  pH adjustment
- Large solids are collected in grates
- Coagulants such as iron(III) chloride are added to neutralize the surface charges
of the suspended particles allowing them to precipitate out.
- Sand filtration is used and membrane filters for smaller particles.
- Chlorine gas Cl2, liquid sodium hypochlorite solution NaOCl (aq) or solid
calcium hypochlorite Ca(OCl)2 are used as disinfectants. They are needed to
ensure the completely remove harmful bacteria such as cryptosporidium and
giardia.
- Constant assessment of the effectiveness of these methods is needed with testing
and public health surveys.
9.4.5.4 Describe the design and composition of microscopic membrane filters and
explain how they purify contaminated water.
These filters have microscopic pores which can reduce or stop the need to chemically
treat the water. They come as microfiltration, ultrafiltration, nanofiltration or reverse
osmosis membranes depending on the size of the pore.
The membrane is made from synthetic polymers in a mixture of solvents.
Semi permeable membranes used in reverse osmosis are either made of cellulose acetate
or a layer of polyamide attached to another polymer. Under pressure these allow passage
of water molecules but not most atoms, ions or molecules.
Water is made to flow across the membrane not through it. This reduces blockage.