Download Acid Rain - Controlled Assessment

Acid Rain - Controlled Assessment
The Science Bit 
During the last century the rain water in some parts of the world has become far more acidic. This acid rain has been
caused by the emission of pollutant gases such as carbon dioxide, sulphur dioxide and nitrogen oxides. When coal is
burned in electricity power stations, gases are released into the atmosphere. Coal (and to a lesser degree Oil and Natural
Gas) contain sulphur. Sulphur dioxide is produced from burning fossil fuels. Power stations burn fossil fuels and the
sulphur dioxide is a product of combustion. Sulphur dioxide gas is acidic and poisonous. If sulphur dioxide gets into the
atmosphere it reacts with water and oxygen in the air to form a dilute solution of sulphuric acid. This sulphuric acid is
the main pollutant in acid rain. Natural rain is slightly acidic due to dissolved carbon dioxide. Natural rain has a pH of 5·5,
acid rain has a pH of 4. The second most important pollutant in acid rain is nitric acid.
Why is acid rain so Acidic?
Acids contain hydrogen Ions. The more hydrogen ions the acid has...the more concentrated the acid is and therefore the
lower its pH.It is the hydrogen ions that give rain water a pH below 5.0. Rain water that has this higher level of acidity
can cause damage to buildings and statues, particularly those made of limestone. It can also reduce the growth of, or
even kill, trees and crops. Acid rain may even lower pH of water in lakes, killing fish.
Acid Rain Damage.
Acid rain kills trees. It runs into rivers and gathers in lakes. Eventually, lakes become too acidic, and plants and fish begin
to die. Acid rain reacts with limestone and damages limestone buildings.When car fuel is burnt sulphur dioxide and
other various nitrogen oxides are produced. When these mix with clouds they dissolve into the water and form
sulphuric and nitric acid. This then falls as acid rain. Acid rain then turns lakes into acidic pools of death which can kill
fish and has a serious effect on the ecosystem. It causes aluminium salts (which are in the ground) to dissolve into the
lake and become aluminium ions which are poisonous to many fish. It also kills trees and damages limestone buildings. It
is prevented by clearing up emissions. Cars and power stations are mainly to blame. Reducing burning of fossils fuels is
also effective.
How to reduce the damage of Acid Rain?
Powdered limestone can be added to soils or lakes to make them less acidic. However...It would be better if we could
avoid or reduce pollutant gas emissions in the first place. Remember...some buildings are made out of marble...acid rain
will erode the stone eventually to from carbon dioxide and water!!!
Science behind Rates of Reaction.
Rate is a measure of how fast or slow something is. In chemistry, we speak of a rate of reaction, this tells us how fast or
slow a reaction is.
Why do chemists want to know the rate of a reaction? If you are making a product, it is important to know how long
the reaction takes to complete, before the product is produced.
Rate is a measure of a change that happens over a single unit time. That unit time is most often a second, a minute, or
an hour.
In order for two reactants to react together:
1. They must collide with each other
2. The collision must be with sufficient energy.
The rate of a reaction depends on how many successful collisions there are in a given unit of time.
The rate of a reaction (speed of the reaction!) may be measured by following the loss of a reactant, or the formation of a
product.
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Rate of reaction = amount of reactant used ÷ time.
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Rate of reaction = amount of product formed ÷ time.
There are 4 methods by which you can increase the rate of a reaction:
1. Increase the concentration of a reactant.
2. Increase the temperature of the reactants.
3. Increase the surface area of a reactant.
4. Add a catalyst to the reaction.
The Effect of Concentration
If the concentration of acid (a reactant) is increased, the reaction occurs at a quicker rate.In dilute acid there are less
acid particles. This means there is less chance of an acid particle hitting a magnesium particle as compared with acid of a
higher concentration.In concentrated acid there are more acid particles, therefore there is a greater chance of an acid
particle hitting a magnesium particle.Remember: the more successful collisions there are the faster the reaction.
The Effect Of Temperature
At low temperatures the reacting particles have less energy. When particles are heated they gain energy. The gaining of
energy enables the particles to move around quicker, this increases their chance of colliding but also, the increase in
energy increases the possibility of a collision occurring with sufficient energy. Therefore rate of reaction increases with
increasing temperature.
The Effect of Surface Area
The rate of reaction between magnesium and hydrochloric acid increases as you increase the surface area of the
magnesium.For example: powdered metal (greater surface area) reacts quicker with acid than strips of metal (lower
surface area).
The Effect of a Catalyst
Some reactions may be speeded up by using a catalyst. A catalyst reduces the energy required for the reactants to
successfully collide. The result is more collisions become successful, hence the rate of a reaction increases.