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REDOX REACTIONS

EXTRACTION OF IRON

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Figure 1. Extraction of iron in blast furnace  

REDOX REACTIONS - A chemical reaction in which reduction and oxidation occur simultaneously. 

Reduction

Oxidation

Oxidation State - The change an atom of an element would have if it existed as an ion in a compound. Refers to the loss, gain, or share of electrons. Charge of element, but sign comes before number (e.g. Na1+ --> Na+1)

OXIDATION

REDUCTION

Hydrogen

Loss

Gain

Oxygen

Loss

Gain

Electrons

Loss

Gain

Oxidation State

Increase in state

Decrease in state

***For Hydrogen and electrons --> OIL RIG (Oxidation is loss, Reduction is gain)

Oxidation Number Rules

1. ELEMENTS BY THEMSELVES ARE 0. (ELEMENTAL/UNCOMBINED FORM e.g. Mg) 

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2. THE OXIDATION OF SIMPLE IONS (Na1+, Mg2+) IS THE CHARGE WITH THE SIGN IN FRONT (e.g. Na1+ --> Na+1, Mg2+ --> Mg+2) 

 

3. OXIDATION NUMBERS IN  A NEUTRAL COMPOUND MUST ADD UP TO 0.  

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Displacement Reaction

OXIDIZING AGENT - Always undergoes reduction itself, oxidizes something

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REDUCING AGENT - Always undergoes oxidation itself, reduces something

Metals are reducing agents (get oxidized) 

Non-metals are oxidizing agents (get reduced) 

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Reactivity Series

Most to Least Reactive 

  • Potassium - K 

  • Sodium - Na

  • Calcium - Ca

  • Magnesium - Mg

  • Aluminum - Al

  • Zinc- Zn     (carbon only)

  • Iron - Fe

  • Lead - Pb

  • Hydrogen - H 

  • Copper - Cu

  • Mercury - Hg

  • Silver - Ag

  • Gold - Au

  • Platinum - Pt 

ELECTROLYSIS

HYDROGEN OR CARBON FOR REDUCTION

VERY UNSTABLE, HEAT TO DECOMPOSE

Disproportionation - Same substance is both oxidized and reduced. E.g. 

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Extracting Metals from Ores

Metals exist in these forms in ores: 

  • Oxides 

  • Hydroxides 

  • Carbonates 

  • Sulphates

Metals can be extracted from their ores through either electrolysis or reduction (using a reducing agent). 

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EXTRACTING ZINC FROM ITS ORE

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CONTACT PROCESS 

EXTRACTING COPPER FROM ITS ORE

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ANOX REDCAT 

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ANOX = Anode oxidation

REDCAT = Reduction cathode 

Electrolysis

Voltage Cell - Converts chemical to electrical energy 

Electrolytic Cell - Converts electrical energy to chemical energy  

Electrolysis - A process used to decompose a compound using current. 

  • molten state (free ions)

  • aqueous state (free ions) 

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Can be used for extracting aluminum from its ore. 

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In electrolysis: 

- Conductor does not get decomposed 

- Electrolyte gets decomposed 

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Ions become discharged at electrodes. 

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Cathode (-)

- Positively charged ions move to negatively charged electrode.

- Ions gain electrons at the cathode

- Reduction always happens at the cathode 

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Anode (+)

- Negatively charged ions move to positively charged electrode. 

- Ions lose electrons at the anode 

- Oxidation always happens at the anode 

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Electrodes

  • Inert - Do not react with products of electrolysis or the electrolyte 

  • Active - React with products of electrolysis or the electrolyte 

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Deposits of metal on electrode are silvery grey color 

Gases are greenish or colorless 

Electroplating / Galvonising - Process of depositing a layer of metal on another substance using electrolysis. 

SELECTIVE DISCHARGE OF IONS IN AQUEOUS SOLUTION

Anions

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Ease of discharge increases

Figure 2. Electrolysis 

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Cations 

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  • K+            Potassium ion

  • Na+         Sodium ion

  • Ca2+       Calcium ion

  • Mg2+      Magnesium ion

  • Zn2+       Zinc ion

  • Fe2+       Iron ion

  • Pb2+      Lead ion

  • H+          Hydrogen ion

  • Cu2+     Copper ion

  • Ag+       Silver ion

Ease of discharge increases

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