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PHS CHEMISTRY 4 2018 - AIR AND WATER (WATER (CHEMICAL TEST FOR WATER add…
PHS CHEMISTRY 4 2018 - AIR AND WATER
WATER
CHEMICAL TEST FOR WATER
add water to anhydrous copper sulfate (white)
⟶ copper sulfate pentahydrate (blue) ⟶ copper sulfate (white) + water
⟶ CuSO4 * 5H2O --> <-- CuSO4 + 5H2O
(--> <-- = reversible equation)
( * H2O = water of crystallisation)
add water to anhydrous cobalt chloride
⟶ cobalt chloride hexahydrate (dark red) ⟶ cobalt chloride (deep blue) + water
⟶ CoCl2 * 6H2O --> <-- CoCl2 + 6H2O
PURIFICATION OF WATER
First, a clean source is needed to pump water from - eg. an aquifer
FILTRATION
- is used to remove solid particles from the water. Water could be filtered through clean gravel or sand. A coagulant chemical could also be added to make small suspended particles stick together - eg iron (III) sulfate
CHLORINATION
- chlorine is added to the water to kill bacteria and other microbes
the water is stored in a clean, covered reservoir, ready for pumping to taps
USES OF WATER
we use water at
HOME
for
drinking
cooking
washing things
flushing toilet waste away
we use water in the
INDUSTRY
for
solvents
cooling
irrigation
diluting chemicals
POLLUTANTS
COMMON POLLUTANTS
in the air and how they are sourced include:
CARBON MONOXIDE - CO
⟶ When combustion is incomplete (limited supply of air), only half as much oxygen adds to the carbon. Therefore instead of making carbon dioxide (CO2), carbon monoxide is made (CO)
⟶ CO reacts with haemoglobin in blood and prevents it from carrying oxygen around the body
SULFUR DIOXIDE - SO2
⟶ Sulfur dioxide is produced from the burning of fossil fuels (coal and oil) and the combustion of mineral ores that contain sulfur
⟶ Sulfur dioxide dissolves easily in water to form sulfuric acid. Sulfuric acid is a major component of acid rain
⟶Irritates eyes and throat, causes respiratory problems.
⟶
Acid rain
attacks stonework in buildings - especially limestone and marble (CaCO3)
NITROGEN OXIDES - NOx
⟶ Nitrogen oxides are produced from the reaction of nitrogen and oxygen gases in the air during combustion - commonly from car exhausts
⟶ Cause respiratory problems
⟶
Acid rain
causes damage to buildings
LEAD COMPOUNDS
⟶ A compound called tetra-ethyl lead is added to petrol in some countries, to help it burn smoothly in engines. On burning, it produces particles of other lead compounds which are dangerous to the environment and deadly to humans
⟶ Lead can damage children's brains and damages kidneys and nervous system in adults
to attempt to reduce the amount of harmful gases being produced in car exhaust,
catalytic converters
have been used in modern cars.
⟶ the harmful gases are absorbed onto the surface of catalysts (usually transition metals), where they react to form harmless gases (speeds up the reaction)
⟶ compounds are either reduced or oxidised eg.
⟶2NO ⟶ N2 + O2
FERTILISERS
A fertiliser is any substance that makes soil more fertile: whether it be natural (animal manure) or synthetic (compounds made in factories)
NITROGEN
- plants need nitrogen for making chlorophyll and proteins
POTASSIUM
- helps plants to produce protein and resist disease
PHOSPHORUS
- helps roots to grow and crops to ripen
AIR
clean and dry air is made up of
21% oxygen
78% nitrogen
the rest is made up of a mixture of noble gases, water vapour and carbon dioxide
OXYGEN
SEPARATION OF AIR
The air is cooled until it turns into a liquid
Then the mixture is separated by fractional distillation - as the gases in the air have different boiling points and can be collected one by one
fractional distillation of liquid air
USES OF OXYGEN
In hospitals, patients with breathing problems are given oxygen through an oxygen mask or in an oxygen tent (plastic tent that fits over bed). Oxygen-rich air is pumped into it
A mixture of oxygen and the gas acetylene (C2H2 - hydrocarbon) is used as the fuel in
oxy-acetylene torches
for cutting and welding metal. When this gas mixture burns, the flame can reach 6000°C. Steel melts at 3150°C, so the flame cuts through it by melting it
CARBON DIOXIDE
FORMATION
COMBUSTION (of fuels)
⟶ natural gas or methane can be burned to create carbon dioxide
⟶ methane + oxygen ⟶ carbon dioxide + water + energy
⟶ CH4 (g) + 2O2 (g) ⟶ CO2 (g) + 2H20 (l) + energy
RESPIRATION
⟶ respiration is the process that takes place in our cells to provide energy
⟶ glucose + oxygen ⟶ carbon dioxide + water + energy
⟶ C6H12O6 (aq) + 6O2 (g) ⟶ 6CO2 (g) + 6H2O (l) + energy
ACID AND CARBONATE REACTION
⟶ carbonates are compounds that contain the carbonate ion CO3 (2-)
⟶ carbonates react with acids to form a salt, water and carbon dioxide
RUST
PREVENTION
OF RUST (corrosion of iron and steel)
paint
⟶ steel bridges and railings are usually painted
grease
⟶ tools and machine parts are coated with grease or oil
sacrificial anode
⟶ during rusting, iron is oxidised (loses electrons). Magnesium is more reactive than iron and has a stronger drive to lose electrons. A bar of magnesium can be attached to the side of a steel ship and it will corrode instead of the iron
galvanising
⟶ the iron object is coated in a thin layer of zinc, stopping oxygen and water reaching the iron underneath. The zinc also acts as a sacrificial metal. Zinc is more reactive than iron, so it oxidises in preference to the iron object.