Module 4: Chemistry in action summary

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Formulae

Word equations

methane + oxygen ---> carbon dioxide + water
methane + oxygen ---> carbon monoxide + water
calcium carbonate ---> calcium oxide + carbon dioxide
calcium oxide + water ---> calcium hydroxide
copper carbonate ---> copper oxide + carbon dioxide
ammonia + nitric acid ---> ammonium nitrate
glucose ---> ethanol + carbon dioxide
ethane ---> ethene + hydrogen

Balanced chemical equations

CH₄(g) + 2O₂(g) ---> CO₂(g) + H₂O(l)
CaCO₃(s) ---> CaO(s) + CO₂(g)
NH₃(g)  + HNO₃(aq) --> NH₄NO₃(aq)

ionic equations

H⁺(aq) + OH^-(aq) ---> H₂O(l)

Crude oil

4.01 Crude oil formation
As sea plants and animals died, they were immediately covered by sediment in seas or swamps. This stopped them decaying aerobically. Further layers of sediment buried the remains deeper and deeper underground and after millions of years of pressure and heat, these remains turned into coal, oil and natural gas.

4.02 Hydrocarbons
Hydrocarbons are compounds which contain only carbon and hydrogen.

4.03 Crude oil as a mixture
Crude oil is a mixture of lots of substances.  It contains alkanes and alkenes.

4.04 Fractional distillation
Fractional distillation separates liquids with close boiling points.
Fractional distillation is lots of little distillations in a fractionating column.

4.05 Fractional distillation of crude oil
The fractional distillation of crude oil is the process which gives us the different fuels made from crude oil. The crude oil is pumped in to the fractional column from the bottom. The heat is applied at the bottom of the fractional column. The different fractions are obtained in different positions in the column.

Top      Gas

            Naptha

            Kerosene

            Diesel

            Fuel oil

Bottom Bitumen

4.06 Uses of fractions

4.07 Size and properties of fractions

Burning fuels

4.08 Complete combustion
Happens with plenty of oxygen.  All of the carbon and hydrogen in a hydrocarbon turns to carbon dioxide and water.  The things made are harmless.

4.09 Oxidation
This is a chemical reaction of something with oxygen.

4.10 Incomplete combustion
Happens if there is not enough oxygen.  The hydrocarbon turns into soot or carbon dioxide.  The things made are harmful.

4.11 Carbon monoxide
This is a poisonous gas. It has no colour or smell so is hard to detect.  If you breathe it in enough it replaces oxygen in the blood and suffocates you.

4.12 Dangerous heating appliances
A faulty gas heater can produce carbon monoxide and be dangerous.  Heaters using other fossil fuels can also be dangerous in the same way.

Plastics

4.13 Useful hydrocarbons from cracking
C-C-C-C-C-C-C-C-C-C-  ----cracking----->    C=C + C=C-C +  C-C=C + C=C
big molecules                                                  small molecule
alkanes                                                            alkenes
single bonds                                                    double bonds
saturated                                                          unsaturated
only good for fuels                                          can be made into polymers

4.14 Conditions for cracking
For cracking we need a high temperature (800^oC) and a catalyst.

4.15 Saturated and unsaturated hydrocarbons
Alkanes are saturated hydrocarbons.  They have single C-C bonds only.
Alkenes are unsaturated hydrocarbons.  They have double C=C bonds.

4.16 Formulae and Structures of alkanes

Ethane C₂H₆
    H H
     |   |
H-C-C-H
     |   |
    H H

Propane C₃H₈
    H H H
     |   |   |
H-C-C-C-H
     |   |   |
    H H H

Butane C₄H₁₀    
    H H H H
     |   |   |   |
H-C-C-C-C-H
     |   |   |   |
    H H H H

4.17 Formulae and Structures of alkenes

Ethene C₂H₄
 H  H
  |    |
 C=C
  |    |
 H  H

Propene C₃H₆
    H H  H
     |   |    |
H-C-C=C-H
     |
    H

4.18 Bromine with alkanes and alkenes

4.19 Addition polymers
lots of monomers add together --->  1 addition polymer
Each has C=C bonds                       only single bonds
unsaturated                                       saturated
lots of ethene molecule   --->            1 polyethene molecule
H   H   H  H      H  H                               H  H  H  H  H  H  H  H
 |     |     |     |       |    |                                 |    |    |    |    |    |    |    |
C=C + C=C +  C=C + .... --->              -(C- C- C- C-C- C- C- C)-_n
 |    |      |     |       |    |                                 |    |    |    |    |    |    |    |
H  H    H   H     H  H                               H  H  H  H  H  H  H  H

4.20 Uses of polymers

4.21 The disposal of plastics

Biodegradable plastic rot faster than other sorts.  They are more expensive to make.

Enzymes

4.22 Uses of enzymes
Enzymes are biological catalysts.  They speed up reactions.  They work best around body heat (37^oC).  They break up (denature) and stop working if the temperature rises much above above 40^oC.  
Enzymes are found in biological washing powder. Enzymes in yeast are used to help fermentation  in making bread and beer.  

 

4.23 Enzymes in the dairy industry
The dairy industry uses milk.  In yoghurt making enzymes turn a sugar in milk called lactose into lactic acid.  Rennin is an enzyme used to turn milk into cheese

Types of chemical reactions

4.24 Types of chemical reactions
neutralisation - an acid reacts with an alkali (or base)
oxidation - Something reacts with oxygen.
thermal decomposition - a compound breaks up when heated.

4.25 Neutralisation
nitric acid is neutralised to form salts called nitrates
ammonia + nitric acid ---> ammonium nitrate
NH₃(g)  + HNO₃(aq) --> NH₄NO₃(aq)
ammonium nitrate is a good fertiliser
sulphuric acid is neutralised to give salt called sulphates
hydrochloric acid is neutralised to give salts called chlorides

4.26 Thermal decomposition
                          heat
calcium carbonate ---> calcium oxide + carbon dioxide
CaCO₃(s) ---> CaO(s) + CO₂(g)
limestone         lime
                          heat
copper carbonate ---> copper oxide + carbon dioxide
CuCO₃(s) ---> CuO(s) + CO₂(g)

4.27 The reaction of water and calcium oxide
calcium oxide + water ---> calcium hydroxide
 CaO(s) + H₂O(l) ---> Ca(OH)₂(s)
quicklime                    slaked lime
Ca(OH)₂(aq) or calcium hydroxide solution is called limewater

4.28 Neutralising soil acidity
Plants need soil that is nearly neutral.  If soil is too acidic plants do not grow.
Calcium oxide and calcium hydroxide are bases.
They react with acids so can be used to neutralise acidic soil. e.g.
nitric acid + calcium oxide ---> calcium nitrate + water
acid in soil    base                          neutral

4.29 Uses of calcium carbonate
Limestone is calcium carbonate.
Limestone is added to iron ore in blast furnace to make iron.
Limestone is heated with clay in a kiln to make cement.
Limestone is heated with sand and sodium carbonate to make glass