Chapter 11: Chem (REDOX) Redox

Redox reaction

chemical reaction involving the transfer of electrons between chemical species

Oxidation

Chemical reaction in which a chemical species loses electrons

Reductant (reducing agent)

the thing that causes reduction in the other substance. It gives electrons away, so it gets oxidised 

Oxidant(oxidising agent)

 the thing that causes oxidation in the other substance. It takes electrons, so it gets reduced

Half-equation 

reduction or oxidation equation of a complete redox reaction

Oxidation state

number assigned to an atom that can be used to determine the movement of electrons in redox reactions Oxidise cause a chemical species to lose electrons

 Oxidising agent

Chemical species that oxidises another substance by accepting electrons

Polyatomic ion

ions made up of a group of atoms covalently bonded together

Reduce

cause a chemical species to gain electrons

Reducing agent

chemical species that reduces another substance by giving away electrons

Reduction

chemical reaction in which a chemical species gains electrons

OILRIG (acronym)

Oxidation Is Loss; Reduction Is Gain

Is this a oxidation reaction or reduction?  Zn(s)--> Zn²⁺ (aq)+ 2e-

Oxidation reaction

In the following equation, copper has undergone which process? Cu²⁺(aq)+ 2e-  → Cu(s)

Reduction

What are half-equations used for?

Used to represent oxidation and reduction; Its determined by the valence electrons an atom can lose or gain

A reduction half-equation will have the electrons on the reactants (LHS) side of the equation  

Ok

An oxidation half-equation will have the electrons on the products (RHS) side of the equation  

Ok

Write the oxidation half-equation and the reduction half-equation: 2Mg(s)+O2(g) → 2MgO(s)   

 Oxidation: Mg(s)-->Mg²⁺ (s)+2e^-   Reduction: O2(g)+4e^-  →O^2-  (s)

Oxidation state of a free element (an element by itself or bonded to itself) is always zero 

O2, C, Cl2

Oxidation state of a simple ion is equal to the charge of the ion

Na⁺ , Cl^- , O2^-, Al³⁺

The sum of oxidation states in a neutral compound is 0

 KCl, CO2, MgSO4

The sum of oxidation states in a polyatomic ion is equal to the charge of the ion 

 SO4 2-, NH4 +, MnO4 -

The normal oxidation state for hydrogen in a compound is +1

HCl, HF, NH3

The normal oxidation state for oxygen in a compound is –2

H2O, CO, NO3

Oxidation number 

Total number of electrons an atom can gain or lose

State the oxidation number for the underlined species: i)KMnO4  ii)H2SO4

i) K=1, O=-2x4=-8+1+Mn-8=0, therefore Mn=+7

ii)H=+1x2=+2, O=-2x4=-8,+2+S-8=0, therefore S=+6

KOHES (acryonum) Key element, Oxygen, Hydrogen, Electrons, States

1. Key elements need to be balanced 

2. Oxygen atoms need to be balanced with water molecules, H2O(l) 

3. Hydrogen atoms need to be balanced with hydrogen ions when in acidic conditions, H+ (aq).

4.  Electrons need to be added to balance charge on each side of the equation, e-.

5. States need to be included.

If an atom's oxidation number increases in a reaction, it has been oxidised, and if it decreases, it has been reduced.

True

A redox reaction doesn’t include electrons in its equations

True

Metal displacement reaction 

Redox reaction in which a more reactive metal displaces a less reactive metal’s cation from solution

Reactivity series of metals

organised scale of metals and their cations, ranked according to their strength as reducing and oxidising agents

Spontaneous redox reaction

feasible redox reaction that occurs without the addition of any extra heat or energy

Spontaneously

where the product formation is favoured

Stronger oxidising agents will appear _____in the reactivity series

higher

Stronger reducing agents appear _____ in the reactivity series

lower

The reactivity series can be used to predict whether a redox reaction is likely to occur

True

Anode

 negatively charged electrode in a galvanic cell where oxidation occurs

Anion

negative ion formed when an atom gains one or more valence electrons

Cathode

 positively charged electrode in a galvanic cell where reduction occurs

Cation

positive ion formed when an atom loses its valence electron(s)

Corrosion

occurs when some metals react with gases in the atmosphere (mainly oxygen)

Dry corrosion

oxidation of metals due to oxygen in the air

Electrode

electrically conductive medium

Galvanic cell

electrochemical cell in which chemical energy from spontaneous redox reactions is converted into electrical energy

Galvanised 

 coated with zinc

Rust

 a flaky, reddish precipitate formed from the corrosion of iron with water and oxygen

Sacrificial anode

a readily oxidised anode used to coat other metals for protection against corrosion

Sacrificial protection

the use of a protective layer that is readily oxidised

Salt bridge

 device used to separate the solutions in each half-cell whilst completing the circuit

Wet corrosion 

oxidation of metals due to oxygen and water in the air

How does dry corrosion happens?

  Refers to the oxidation of a metal by oxygen gas. This is usually prevented by coating reactive metals with a sacrificial metal. This usually occurs at a slow rate   

How does wet corrosion happen?

Refers to the oxidation of a metal with oxygen gas AND water, The presence of water accelerates the rate of reaction. This is usually prevented by using a more reactive metal as a sacrificial metal

Oxidation occurs at the ____

Anode

Reduction occurs at the _____

Cathode

Electrons travel from the anode to the cathode, creating a current

True

Galvanic Cell

The apparatus that turns chemical energy into electrical energy harnessing a spontaneous redox reaction.