Unit2b.6

Unit 2B.6 Mining and Refining

Oxidation-Reduction reactions “aka” Redox Reactions • Redox reactions involve the transfer of electrons from one species (atom, ion, molecule) to another • Oxidation actually means the loss of electrons The species that loses the electrons is said to have been oxidized • Reduction actually means the gaining of electrons The species that gains the electrons is said to have been reduced Oxidation and reduction occur simultaneously as electrons are not lost in chemical reactions – Redox reactions (reduction-oxidation reactions)

OIL RIG

Oxidation Is Loss of electrons Reduction Is Gain of electrons

Redox reactions are useful in mining because they produce the free metal If the ore contains metal ions they can be REDUCED to give the solid metal

Cu+2 + 2e-→ Cu(s) • To do this one needs to find a substance or process that will provide the electrons needed for reduction One method uses a solid metal that was higher on the Activity series to provide the electrons

Cu+2 + Mg (s) → Cu(s) + Mg+2

ALL Redox reactions require a source of electrons

Electrometallurgy 



Uses an electrical current to supply electrons to metal ion Reduces them

Pyrometallurgy 

Using heat and Carbon (coke) or Carbon monoxide (carbon supplies the electrons)

Hydrometallurgy 

Treating ores with reactants that are in solution

We can visually represent a redox reaction using:

Electron Dot structures Shows the valence electrons of the neutral element that can be transferred  Valance electrons are the electrons in the outermost electron layer or shell 

•Let’s look at a magnesium atom. Magnesium is in the Alkaline Earth Metal family, and it has two valance electrons. •The valence electrons are represented by the dots next to the chemical symbol for Magnesium (Mg). •Place dots one at a time, counter clockwise.

Mg

Let’s Practice Write the Electron Dot structures for Ca, N, C, Br, Kr.

Your Answers

Let’s see how electron dot structures are used to visualize redox reactions.

When reactive metals like magnesium form ions, they lose their valance electrons.

Mg → Mg+2 + 2eMg releases its valence electrons = LOSS

This is Oxidation

More Examples Zn 2eCu 2ePb 3e

→ Zn+2 →

+

Cu+2 +

→ Pb+3 +

Reduction Reduction is the opposite of oxidation. In reduction, the metal ion gains electrons to become an atom Mg receives electrons = GAIN

Mg+2 + 2e- → Mg This is Reduction

Ore to Metal Ores are metal and stone amalgams or mixtures. When a metal is in an ore, it exists as an ion

Malachite, a copper containing ore, contains copper ions.

Ores to Metals One way to free the metal ions, is to react the ore with a more reactive metal. Remember oxidation and reduction happen at the same time. In this reaction the result is copper metal.

Cu

+2

+ Mg

→ Cu +2

+ Mg

Redox reactions Redox reactions can only take place if the more reactive metal is the reducing agent In other words the more reactive metal is in its elemental form. Use the metal active series There must be the same number of electrons lost as gained for a redox reaction to occur

Oxidizing Agent 



Substance that causes another to be oxidized. Is reduced itself

Reducing Agent 



Substance that causes another to be reduced. Is oxidized itself

Half Reactions We use half reactions as another way of visualizing what is taking place in a Redox reaction.

Cu+2 + Mg → Cu Mg+2

Oxidizing Cu+2 + 2e- → CuAgent +2 Mg → Mg +Reducing Agent 2e-

This is Reduction This is Oxidation

+

Homework Go to Quia.com Use your new usernames and passwords. Complete the assignment Homework: Unit 2B.6.