Chemistry Topic 6 - Redox Reactions

Checklist

1. Assigning & Using Oxidation Numbers

2. Half & Combining Equations

3. Metal Reactivity

4. Redox Reactions (Galvanic and Electrolytic Cell)

5. Batteries (Primary + Secondary Cells)

6. Corrosion

What is the oxidation number of an atom of a pure element?

The oxidation number of an atom of a pure element is equal to zero.

What is the oxidation number of both atoms in a homonuclear diatomic molecule?

The oxidation number of both atoms in a homonuclear diatomic molecule is equal to zero.

Homonuclear Diatomic Molecule: Molecule made up of 2 of the exact atoms of the same element.

What is the oxidation number of a monatomic ion?

The oxidation number of a monatomic ion is equal to its ionic charge.

What is Rule 4 for assigning oxidation numbers?

The sum of the oxidation numbers of all atoms in:

1. A neutral molecule (eg H₂O, CO₂) equals zero

2. A polyatomic ion (eg SO₄^2-) is equal to the charge of the ion.

Example:

SO₄^2- – we need to give oxidation numbers to all atoms in the molecule. Since SO₄^2- is a polyatomic ion (has a charge), the sum of all the oxidation numbers must equal the charge, which is -2.

What is the oxidation numbers of metals in groups 1, 2,

In their compounds:

1. Group 1 metals have an oxidation number of +1.

2. Group 2 metals have an oxidation number of +2

What is the oxidisation of the non-metals: fluorine, hydrogen, oxygen, group 7’s, group 6’s, and group 5’s.

In their compounds, non-metals are assigned oxidation numbers according to the list:

Fluorine: -1

Hydrogen: +1

Oxygen: -2 (+2 in peroxide: H₂O₂)

Group 7: -1

Group 6: -2

Group 5: -3

What is the oxidation number of a neutral molecule (H₂O)?

Equals to 0

What is the oxidation number of a polyatomic ion (SO₄^2-)?

Equals to the charge of the polyatomic ion

What is the Analogy used to balance half equations?

All

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What does A stand for in AOHC?

Balance Atoms other than O or H

What does O stand for in AOHC?

Balance Oxygens by adding H2O

What does H stand for in AOHC?

Balance Hydrogens by adding H+

What does C stand for in AOHC?

Balance Charge by adding e-

What is the flow of Hydrogen atoms in Oxidization and Reduction

Oxidation – loss of hydrogen

Reduction – gain of hydrogen

What is the flow of Oxygen atoms in Oxidization and Reduction

Oxidation – gain of oxygen

Reduction – loss of oxygen

What is the flow of electrons in Oxidization and Reduction

Oxidation – loss of electrons

Reduction – gain of electrons

True of False: Reduction is a decrease of the oxidation number

True!

What is the role of the Salt Bridge in Galvanic Cells?

Balances the charge between the solutions in the half cells, where anions flow to the positively charged solution to balance in, and cations flow to the negatively charged solution to balance it.

How do you determine which is the Cathode and Anode in a Galvanic Cell?

Compare the charge of both solutions, the higher positive charged one is the anode as the half cells is losing more electrons thus making it a higher positive charge.

What is the charge of the Anode and Cathode in Galvanic Cells

Cathode is +ve

Anode is -ve

What type of electrochemical cell is involved in Primary Cells. Describe it, provide an example and its benefits.

Galvanic Cells, AA or AAA Batteries, Cheap & No preparation

What type of electrochemical cell is involved in Secondary Cells. Describe it, provide an example and its benefits.

Galvanic and Electrolytic Cells, Car or Phone Battery, Environmentally Friendly and Can be reused for much long and longer than a primary cell.

What occurs in the formation of rust in terms of the Cathode and Anode Sites?

1. Steel (Fe³⁺) is formed at through oxidization the anode site where Fe forms in to Fe³⁺ + 3e^-.

2. Hydroxide (OH^-) is then formed at the cathode site through reduction where Electrons, Oxygen, and Water react to form hydroxide.

Oxygen has high electronegativity and metla shave low electronegativity, therefore metal commonly lose electrons to oxygen

What does rust do?

Weakens the atoms of metals through oxidisation

How do you prevent corrosion

1. Inert/unreactive coating

2. Inert/unreactive metal coating (gold, silver, etc)

3. Metal reacting with oxygen to form metal oxides as a protective layer (chromium, nickel, and aluminium).

4. Sacrifical more reactive metals

What would be a suitable electrolyte for a electroplating cell?

An electrolyte with the ion of the material that the object is being electroplated in (anion) so the ion can transport to the cathode and be plated through reduction

How do you write a single displacement reaction (predicting the reaction)

Determine the metal and the ion (in solution), figure out whether the metal is more reactive than the ion and whether it will react and the ion will give electrons to the metal.

Why do Cations in electrolyte undergo Reduction?

They travel towards the negatively charge cathode to gain electrons.

batteries: galvanic (electrical) to electrolytic (Chemical)

galvanic + electrolytic cells with metal rea