C3 – Unit 4

Fuels

Coal was ground to a fine powder and burned in oxygen. The oxygen was produced by decomposing potassium permanganate.

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The reaction glowed very brightly as heat was produced. So much heat the test-tube melted.

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A heated piece of charcoal was plunged into a gas jar containing oxygen.

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This gave a violent bright reaction.

The gas produced was tested and proved to be carbon dioxide –  CO2
(lime water goes cloudy in the presence of carbon dioxide).

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The carbon dioxide is heavier than air and pours downwards.

(Thanks Charlie for the photos)

Both coal and charcoal are impure forms of the element carbon.

A fuel is a substance which burns to release heat energy.

word equation

carbon + oxygen → carbon dioxide

symbol equation

C + O2 → CO2

Model kits for breaking/forming bonds

 

Exothermic Reactions


carbon + oxygen


carbon dioxide

Energy is required to break bonds and released when forming bonds. Here there are more bonds broken ( 2 x O-O bonds) than formed ( 4 x C-O bonds. This is a very rough explanation . Reactions which release energy are described as exothermic.

 

Fires and fire safety

Three things are needed for a flame – shown by the fire triangle

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Remove any one and the fire will go out.

Fire extinguishers

  1. Water – removes heat
  2. Carbon dioxide – removes oxygen
  3. Powder – removes the fuel.

A fire map was completed of the ground floor of the school showing all appliances to protect the school form going on fire – fire hoses, fire extinguishers, fire blankets, fire doors and fire alarms.

Chip pan fire – thanks Mr. Phillips for risking all!

Never put water on a chip pan fire. The water boils and blows the blazing oil everywhere. This applies to all liquid fires.

  1. Remove the heat
  2. Cover with a well wrung damp cloth
  3. Leave until cool

 

The Fossil Fuels

Looked at film on Chemicals from Oil and completed question sheet –

Crude Oil – thick black liquid

Separated by fractional distillation

A fraction is a group of chemicals within a given boiling range

First fractions – colourless, evaporate easily, burn easily, runny

Later fractions – dark, high boiling points, don’t burn, thick

Industrially separated by using fractionating column or tower

Uses of fractions – gases as domestic heating fuels, naphtha for making chemicals including petrol, kerosene as aviation fuel, diesel as a fuel for heavy transport, oils for lubrication, greases and waxes also for lubrication and candles, bitumen for roads and roofs

Crude oil contains a mixture of hydrocarbons

 

Combustion of hydrocarbons

Experiment on the combustion of heptane – a fraction from crude oil. The products of combustion were drawn through a U-tube and a bubbler containing lime water.

(thanks Iona)

The lime water showed that Carbon Dioxide (CO2) was formed and condensation in the U-tube showed that it also produced water (H2O).

Hydrocarbons are composed of the elements hydrogen and carbon

 

Balanced equations

Looked at balancing equations

All Chemical reactions obeys the “Law of Conservation of Mass”

Every atom of reactant must show up in the product

methane + oxygen → carbon dioxide + water

CH4 + O2 → CO2 + H2O

there are 4 hydrogens on the left there must be 4 on the right – multiply the water by 2

CH4 + O2 → CO2 + 2H2O

there are now 4 oxygens on the right so multiply the oxygen by 2

CH4 + 2O2 → CO2 + H2O

This is now a balanced equation

For heptane as in today’s experiment

C7H16 + O2 → CO2 + H2O

There are 7 carbons on the left, 7 are needed on the right – multiply carbon dioxide by 7

C7H16 + O2 → 7CO2 + H2O

There are 16 carbons on the left, 18 are needed on the right – multiply the water by 8

C7H16 + O2 → 7CO2 + 8H2O

There are now 22 oxygen atoms on the right so the oxygen molecule on the left needs to be multiplied by 11

C7H16 + 11O2 → 7CO2 + H2O

Biofuels and Biomasses

Internet research was carried out on biofuels and biomasses.

 

Visit to boiler room

A visit was made to the boiler room to see how fuel was used to heat the school.

Storage tanks

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A big fuel gauge!

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Connected by a load of pipes

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Three boilers

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Control panel

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In winter the boilers can use 1000 litres of fuel per day! This doesn’t usually drop below 500 litres per day. At 1000 litres per day – that is £750 per day to run,

It is easy to see why heat should be saved. As well as being expensive resources are being used up.

Visit to Biomass boiler

A Biomass boiler, using wood pellets as fuel, has been installed to augment the schools heating system.

 

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The wood pellets can just be seen through the glass.

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Thanks to Cammy the janitor for the visit, thanks Tammy and Shannon for the pictures.

 

Pollution problems arising from the combustion of fuels

1. Oxides of nitrogen

A high voltage was passed through a flask of air for a period – producing and electric spark

A brown gas formed

At the end water and universal indicator solution was added

The solution was acidic

A mixture of oxides of nitrogen form

N2 + O2  →  NO2

When the oxides dissolve in water a solution of nitric acid is formed.

NO2 + H2O + ½O2  →  HNO3

The temperature of the spark is high enough to break the nitrogen N2 bonds and allow it to react with oxygen. This happens in petrol engines. The spark plugs produce an electric spark and air is drawn into the engine for the fuel to burn.

This happens naturally when there is lightening.

This all leads to acid rain.

 

2. Sulphur dioxide

Sulphur was put in a burning spoon, set alight and plunged into a gas jar containing oxygen.

Sulphur burns to produce sulphur dioxide

S + O2  → SO2

Universal indicator solution was added to the sulphur dioxide produced

Sulphur dioxide is very soluble in water giving an acidic solution – it forms sulphurous acid which oxidises in air to sulphuric acid

SO2 + H2O  →  H2SO3

It is so soluble it gives rise to a fountain experiment. A flask containing sulphur dioxide and equipped with a jet is put in water with universal indicator solution added to it. A little water has to be persuaded to go into the flask to get the fountain started.

As the sulphur dioxide dissolves in the water it causes a pressure drop. The higher air pressure outside the flask causes the water to move into the lower pressure in the flask (it gets ‘sooked’ up). Sulphur dioxide also leads to acid rain

Manufacturers of fuels now try to remove the sulphur

Acid rain affects lakes, rivers, and streams. The pH becomes too low to support aquatic life.

It can significantly damage forests. Trees loose leaves, have damaged bark, and stunted growth.

Acid rain also has an impact on architecture causing building materials to disintegrate.

Acid rain can also corrode metals – cars, railroad tracks, steel bridges, etc.

 

3. Incomplete combustion

Carbon, and carbon monoxide, a poisonous gas, are produced when hydrocarbons burn in a limited supply of oxygen

CH4 + O2  →  CO + H2O

CH4 + O2  →  C + H2O

Lead compounds which were once added to petrol cause pollution.

Air pollution from the burning of hydrocarbons can be reduced by special exhaust systems or by altering the fuel to air ratio

Transition metal catalysts in the exhaust can convert the pollutant gases to harmless gases

CO + O2  →  CO2

NO2  →  N2 + O2

Decreasing the fuel to air ratio improves the efficiency of combustion thus decreasing pollution

An experiment to collect and analyse car exhaust samples was carried out. Pupils have produced a webpage – to be updated.

This topic was so long that next year it may be split into two – Fuels and Pollution.

CFE Outcomes

Level 4

I have explored how different materials can be derived from crude oil and their uses. I can explain the importance of carbon compounds in our lives.

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I can monitor the environment by collecting and analysing samples. I can interpret the results to inform others about levels of pollution and express a considered opinion on how science can help to protect our environment.

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National 4

Fuels
Formation and extraction processes for crude oil. Fractional distillation, cracking

A fuel is any compound that has stored energy.

Energy is released during burning/oxidation. The most common form of oxidation is the direct reaction of a fuel with oxygen through combustion.

Wood, petrol, coal, peat and any number of other fuels have energy-rich chemical bonds created using the energy from the Sun, which is released when the fuel is burned.
Chemical fuels or the fossil fuels are useful reserve of fuels and are therefore used extensively to satisfy the demands of an energy-dependent world.
Fossil fuels are principally hydrocarbons with minor impurities. They are so named because they originate from the decayed and fossilised remains of plants and animals that lived millions of years ago. They are a finite resource.
Crude oil is a mixture of hydrocarbons.
Combustion is the reaction of burning a fuel in oxygen. Controlling fires can be explained through the fire triangle.
Hydrocarbons burn in a plentiful supply of oxygen to produce carbon dioxide and water.
Carbon monoxide, a poisonous gas, and carbon are produced when hydrocarbons burn in a limited supply of oxygen. In engines, catalytic converters can be used to minimise the output of carbon monoxide

Exothermic chemical reactions produce energy and endothermic chemical reactions take in energy. Combustion is an example of an exothermic reaction.
Finite energy sources will be investigated in conjunction with the development of biofuels as alternative sources of energy to support society’s energy needs.

Biomass, a source of biofuels, is plant-based material which can be burned to release energy. Biomass can also be converted to other usable forms of fuel. These include methane gas or fuels used for transportation such as ethanol and biodiesel.