Chemical Processes

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Fuel Cells (C6)

1.       Hydrogen gas (the fuel) enters the cell.

2.       Hydrogen is oxidised to H+ ions (protons) at the anode. 2H2          =        4H+ + 4e-

3.       The protons move through the proton exchange membrane and the electrolyte.

4.       Electrons pass through the external circuit.

5.       Oxygen gas enters the cell.

6.       Oxygen is reduced at the cathode. O2 + 4H + 4e-        =             2H2O

7.       A platinum catalyst accelerates the reactions at the electrodes.

8.       Water is produced. 

NB: The above is for an acidic electrolyte, the following are the equations for an alkaline electrolyte:

Anode: H2 + 2OH-     =    2H2O + 2e-   

Cathode: O2 + 2H2O + 4e-  =  4OH-

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Preventing Rust (C6)

1.       Painting iron

2.       Coating iron in oil/grease

3.       Alloying the iron

4.       Electroplating the surface with tin

5.       Sacrificial Protection

6.       Galvanising:

·         A form of sacrificial protection.

·         Zinc is electroplated onto the surface of the iron.

·         The zinc coating prevents air and water from reaching the iron.

·         Zinc is more reactive and more readily oxidised.

·         Zinc is therefore more likely to react than the iron-it sacrifices itself.

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Making alcohols (C6)

Fermentation:

  • 1. Plants that make the glucose are grown (Biomass).
  • 2. Yeast is added to the glucose solution under anaerobic conditions.
  • 3. A temperature of 25-50οC is used.
  • 4. Ethanol and carbon dioxide are produced. 

Hydration:

  • 1.Crude oil is cracked to produce ethene.
  • 2.Water is heated to make water vapour.
  • 3.The ethene and water vapour are passed over a hot phosphoric acid catalyst to produce ethanol.
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Comparing Fermentation and Hydration (C6)

Feature                Fermentation of sugars                    Hydration of ethene

Conditions             Low temperatures (25-50οC)             High temperatures

                              Normal pressure                              High pressure

Raw materials         Sugar from plants renewable)           Ethene from crude oil (non-renewable)

Purity of product   Low-filtration and distillation required High-no by products

Percentage yield    Low (approximately) 51%                  High – 100%

Atom economy       51%                                                100%

Type of process    Batch                                              Continuous 

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Ozone Layer Depletion (C6)

1. (Initiation) The ultraviolet rays break a bond in the CCl2F2 molecule. A chlorine radical and a CClF2 radical are produced.  Ultraviolet light + CCl2F2    =   οCClF2 + Clο

2. (Propagation) The chlorine radical reacts with the ozone (O3) to form a ClO radical and an oxygen (O2 molecule). The ClO radical then reacts with another ozone molecule to form another chlorine radical and two more oxygen molecules. In this way the chlorine radical is regenerated.

Clο + O3     =    ClOο + O2 

ClOο + O3    =  Clο + 2O2

3. (Termination) Two radicals combine together to form a stable molecule. Either two chlorine radicals could combine together or a CClF2 radical and a chlorine radical could react together.

 Clο + Clο    =     Cl2

[OR]

οCClF2 + Clο    =   CCl2F2

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Saponification (C6)

  • 1.       Vegetable oils are heated in large vats with sodium hydroxide solution.
  • 2.       The reaction spits the oil into glycerol and sodium salts (the soap) of the fatty acids as the hydroxide ions from the sodium hydroxide solution break down the molecules of the oil (they cause the bonds between the fatty acids and the glycerol to break).
  • 3.       Salt is added at the end of the reaction to make the soap precipitate out.
  • 4.       The solid soap is then removed.
  • 5.       Colouring and perfume can then be added.
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Formation of Scum and Scale (C6)

Formation of Scum:

  • 1.       Acid rain causes calcium and magnesium ions from rocks to dissolve into water from mountainous areas, making the water hard.
  • 2.       The soluble calcium (or magnesium) ions react with the soluble stearate ions from soap (when hard water is added to soap) to form insoluble calcium stearate (scum).

Sodium stearate + Ca2+ Calcium stearate + Na+

Formation of Scale:

  • 1.       Acid rain causes calcium and magnesium ions from rocks to dissolve into water from mountainous areas, making the water hard.
  • 2.       Rocks based on calcium carbonate (e.g. limestone) react with the carbon dioxide and water in rain (i.e. acid rain) to form calcium hydrogen carbonate.
  • 3.    The calcium hydrogen carbonate provides calcium ions when dissolved in water that cause temporary hardness.
  • 4.       The calcium hydrogen carbonate forms scum when added to stearate ions but when heated, it thermally decomposes to form calcium carbonate, carbon dioxide and water.
  • 5.       The calcium carbonate is the limescale.   

      Calcium hydrogen carbonate (Hard Water) = Calcium carbonate + carbon dioxide + water

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Softening water (C6)

Using washing soda:

  • 1.       Washing soda is sodium carbonate.
  • 2.       Most carbonates are insoluble but sodium carbonate is soluble, therefore when sodium carbonate is added to hard water, a precipitation reaction occurs:


Ca(HCO3)2 + Na2CO3        =          CaCO3 + NaHCO3

  • 3.       The hard water is softened as the calcium ions are removed as a precipitate.

Using an ion exchange column:

  • 1.   The column contains many beads packed together called resins.
  • 2.       As hard water passes through the column, calcium/magnesium ions from the water attach to the resin and sodium ions leave it.
  • 3.       When all the sodium ions have been removed from the column, the resin can be regenerated by flushing sodium chloride solution through it.
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Hydrogenation (C6)

  • 1. Hydrogen is bubbled through runny oil at 200οC-the hydrogen is being added to double carbon-carbon bonds.
  • 2.       Each double bond requires 2 hydrogen atoms to be converted into saturated, single carbon-carbon bonds.
  • 3.       A nickel catalyst is used.

Image result for hydrogenation

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Removing stains:

Using detergents to remove stains:

  • 1.       Detergents are made by reacting an organic acid with an alkali (salt in the neutralisation reaction).
  • 2.       Detergent molecules have a hydrophilic head and a hydrophobic tail.
  • 3.       The hydrophilic head forms strong intermolecular forces with the water molecules in the wash.
  • 4.       The hydrophobic head forms strong intermolecular forces with the fat/oil molecules in the stain.
  • 5.       The detergent molecules can then surround the oil or fat molecules in the stain and lift them off the clothing fabric into the washing water.

Using dry cleaning to remove stains:

  • 1.       Organics solvents are used as opposed to water to wash the clothes.
  • 2.       Grease molecules have weak intermolecular forces between them.
  • 3.       The organic solvents also contain weak intermolecular forces, allowing them to bind to the grease easily when the two substances are mixed.
  • 4.       There are very strong hydrogen bonds between water molecules. As a result, water cannot stick to grease.
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