Chemistry C1

These revision cards are on the topic of air quality c1

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  • Created on: 03-06-12 18:24

C1 Air Quality- chemicals in the air

  • The earth surrounded by a thin layer of gases called the atmosphere
  • Air forms part of the atmosphere
  • it is a mixture of different gasses consisting of small molecules with large spaces between them
  • Air contains
  •  78% Nitrogen
  • 21% oxygen
  • 1% Argon and other nobel gases
  • There also small amounts of water vapour, carbon dioxide and particulates 
  • The amount of water vapour and polluting gases varies as a result of human activity or by natural process (e.g volcanoes)
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C1 Air Quality- The earths atmosphere. 1

  • Since the formation of the earth 4.6 billion years ago the atmosphere has changed a lot
  • the timescale however is enormous because one billion years is one thousand million (1000,000,000) years

Formation of the earth 4 billion years ago- The earliest atmosphere contained ammonia, water vapour and carbon dioxide. These gases come from inside the earth and were then released through the action of the volcano. 

3 billion years ago- as the temperature of the planet fell the water vapor in the atmosphere condensed to form the oceans and sea

2 billion years ago- the evolution of photosynthesising organisms started to reduce the amount of carbon dioxide in the air and increases the amount of oxygen in the atmosphere. 

1 billion years ago- carbon from carbon dioxide in the air became locked up in sedimentary rocks as carbonates and fossil fuels after dissolving in the oceans

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C1 Air Quality- The earths atmosphere. 2

Now- clean air contains about 

78% Nitrogen 

21% oxygen

1% other gases including 0.035% carbon dioxide

  • Normal air contains varying amount of water vapour and some polluting gases. 
  • The variation in the quantities of these gases is partly due to human activity 
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C1 Air Quality- Pollutants in the air 1

  • Pollutants are chemicals that can harm the environment and our health
  • Pollutants that harm the environment can also harm humans indirectly. 
  • For example acid rain makes the waters in rivers and lakes too acidic for plants and animals to survive
  • This has indirect impact on our food chain and natural resources like trees

Pollutant: carbon dioxide

harmful to: environment

why?: traps heat in earths atmosphere (a greenhouse gas)

Pollutant: nitrogen oxides

harmful to: environment and humans

why?: causes acid rain also causes breathing problems it also makes asthma worse

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C1 Air Quality- Pollutants in the air 2

Pollutant: sulfur dioxide        Harmful to: environment 

why?: causes acid rain 

Pollutant: particulates (small particulates of solids e.g carbon)

Harmful to: environment and humans

why?: makes buildings dirty, makes asthma worse, causes lung infection worse if inhaled

Pollutants: carbon monoxide

Harmful to: humans

Why?: displaces oxygen in the blood, which can result in death.

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C1 Air Quality- Measuring pollutants

  • By measuring the concentrations of pollutants in the air, it is possible to assess air quality
  • The units of measurement used are ppb (parts per billion) or ppm (parts per million)
  • For example a sulfur dioxide concentration of 16ppb means that in every one billion (1000,000,000) molecules of air, 16 will be sulfur dioxide molecules. 
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C1 Air Quality- Data about pollution

  • Data is very important to scientists because it can be used to test a theory or explanation. 

Example

One theory states that carbon monoxide (co) is an example of a pollutant caused by human activity. If this is true carbon monoxide concentrations are likely to be higher in density populated areas e.g cities

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C1 Air Quality- Data about pollution 2

Location              Time                                    (co) Concentration (ppm)

city centre             9:00 am                                5.2

                           10:00 am                                 4.4

                           11:00 am                                 5.0

                           12:00 am                                 2.6

                           1:00 am                                  4.8

Country park        9:00 am                                 0.2

                           10:00 am                                0.1

                           11:00 am                                0.1

                           12:00 am                                0.0

                     1:00 am                                  0.1

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C1 Air Quality- Data about pollution 3

Measurement like this can vary because:

  • Variables (factors that change) like the volume of traffic, and weather affect concentrations
  • All measuring equipment has limited accuracy 
  • The users skill will affect the accuracy of the measurements. 
  • Because measurements vary, it is not possible to give a true value for the concentration of carbon monoxide in the air.
  • However the true value is likely to lie somewhere within the range of the collected data. i.e. between 4.8 and 5.2 in the city centre and 0 and 0.2 in the country park. 
  • The measurement of 2.6ppm has been excluded as it is an outlier in the data range for city park. 
  • Outliers are measurements that stand out as being very different to the other sets of data it normally indicates some sort of error.
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C1 Air Quality- Data about pollution 3

Higher Tier

  • You must be able to say why 2.6ppm is an outlier e.g  the operator may have misread the scale. It is unlikely that the volume of traffic would have decreases at mid-day. In fact you would expect traffic to increase as people leave their work places to go for lunch.
  • It is important measurements are repeated because you can't tell from one set of data if it is reliable or not. Wheres if you have lots of repeats the errors should stand out. 
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C1 Air Quality- Data about pollution 4

  • By calculating the mean (finding the average) of a set of repeated measurements, you can overcome small variations and get a best estimate of the true value. 

Mean= sum of all values              Do not use outliers in mean calculation

          Number of values   

city= 5.2+4.9+5.0+4.8  = 5.0ppm 

               4

Country= 0.2+0.1+0.1+0.0+0.1  = 0.1ppm 

                          5

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C1 Air Quality- Data about pollution 5

  • The mean carbon monoxide concentrations in the city is a lot higher than the mean carbon monoxide concentration in the country.
  • This shows that the data supports the theory that carbon monoxide is a pollutant cause by human activity. 
  • In fact about, half of all carbon monoxide emissions in the UK are produced by road transport, with the rest coming from homes and other industries. 

Higher tier

  • There is a real difference between the mean carbon monoxide concentration in the city centre and the city park
  • Because the difference between the mean values is a lot bigger than the range of each set of data.
  • If the difference had been smaller than the range there would have been no real difference . 
  • The result would have been insignificant and the data would not support the theory. 
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C1 Air Quality- chemicals

  • Elements are the 'building blocks' of all materials.
  • There are more than 100 elements and each one is made up of very tiny particles called atoms 
  • All atoms of a particular element are the same and are unique to that element 
  • Each element is represented by a different chemical symbol, e.g C for carbon, O for oxygen and Fe for iron
  • Atoms can join together to form bigger building blocks called molecules
  • Compounds are formed when 2 or more different elements are chemically combined 
  • The properties of a compound are very different to the properties of the individual element it is made from 
  • Chemicals symbols and numbers are used to unite formulae. Formulae shows:

- The different elements that make up a compound 

- The number of atoms of each different elements in one molecule 

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C1 Air Quality- chemical change

  • During a chemical reaction new substances are formed from old ones. This is because the atoms from the reactants are re-arranged in some way. 

- Joined atoms may be separated        - Separate atoms may be joined       - Joined atoms may be separated then joined again in different ways

  • These chemical changes are not easily reversible 
  • You can show what happens during a chemical reaction by using a word equation reactants on one side and products( newly formed chemicals) on the other side, 
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C1 Air Quality- oxidation and reduction

  • An example of oxidation is a chemical reaction that occurs when oxygen joins with an element or compound
  • An example of reduction is when oxygen is lost from a substance. 
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C1 Air Quality- Combustion

  • Combustion is a chemical reaction when fuel burns releasing energy as heat. 
  • For combustion to take place oxygen must be present
  • Combustion is an example of oxidation.
  • Coal is a fossil fuel which consists mainly of carbon
  • The equation to show what happens to coal when it reacts with air (oxygen) is...

carbon+oxygen ---------------> carbon dioxide

  • This equation tells us that one atom of carbon (C) and one molecule of oxygen (O) produce one molecule of carbon dioxide (CO2)
  • No atoms are lost or produced during a chemical reaction. 
  • So there will ALWAYS be the same number of atoms on each side of the equation therefore conservation.
  • This means there will always be some pollutants formed during the combustion of fuels.
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C1 Air Quality- Combustion (Higher tier)

  • The conservation of atoms during combustion reaction has implications for air quality since some atoms in the fuel may react to give products that are pollutants. e.g carbon monoxide or sulfur dioxide.
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C1 Air Quality- complete combustion

  • Fossil fuels such as: 

- petrol

- diesel fuel 

- natural gas

  • consist mainly of compounds called hydrocarbons
  • Hydrocarbons ONLY CONTAIN Hydrogen and Carbon atoms. So when it is burned in the air carbon dioxide and water (hydrogen oxide) are produced, This is called complete combustion 

Remember: carbon dioxide is a pollutant

  • If the fuel burns in pure oxygen the reaction is much faster than when it burns with air

Methane+Oxygen----------> carbon dioxide+water

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C1 Air Quality- incomplete combustion

  • If a fuel is burned and there is not enough oxygen in the air, carbon particulates or carbon monoxide may be produced.  This is called incomplete combustion. 

Methane+oxygen --------->carbon+water

Methane+oxygen --------D-->carbon dioxide+water

  • Incomplete combustion occurs in car engines.
  • so car emissions contain carbon particulates carbon monoxide aswell as carbon dioxide. 
  • Many samples of coal contain sulfur so when coal burns sulfur dioxide is released intp the atmosphere.

sulfur+oxygen-------->sulfur dioxide

  • During combustion of fuels in high temps e.g in a car engine or powerstation can cause nitrogen in the atmosphere to react with oxygen to produce nitrogen oxide, 
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C1 Air Quality- incomplete combustion Higher tier

Nitrogen dioxide are formed in 2 steps;

Step 1 :

The nitrogen reacts with oxygen to form nitrogen monoxide. 

Nitrogen+oxygen--------->Nitrogen Monoxide 

Step 2:

Nitrogen monoxide is the oxidised to produce nitrogen dioxide. 

Nitrogen monoxide+oxygen----------->nitrogen dioxide. 

  • When NO and NO2 occur together they are called oxides of nitrogen and the are written as NOx 
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C1 Air Quality- what happens to pollutants

  • Pollutants released in atmosphere start causing problems in the environment
  • Carbon particulates appear on stone buildings making them dirty. 
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