Oxidation and Reduction Reaction

Development of oxidation and reduction reaction concept

1. Based on binding and releasing of oxygen

· Oxidation is a reaction in which an element or compound binds a number of oxygen.

Example: rusting of iron reaction

Oxidant is a substance which is a source of oxygen.

· Reduction is a reaction in which an element or compound release a number of oxygen.

Example: reaction between copper (II) oxide and hydrogen gas

Reductant is a substance which binds a number of oxygen.

2. Based on binding and releasing of electron

· Oxidation is a process of releasing a number of electrons.

Example:

· Reduction is a process of binding a number of electrons.

Example:

Oxidant is a substance which bind electron.

Reductant is a substance which release electron.

Basically, the process of oxidation and reduction reaction is happened simultaneously, which called redox reaction. Pay attention the redox reaction in the following process of sodium chloride formation.

3. Based on increasing and decreasing of oxidation number

· Oxidation is a chemical reaction in which happens increasing of oxidation number.

· Reduction is a chemical reaction in which happens decreasing of oxidation number.

Example:

In the reaction above, Na is a reductant because it undergoes the increase of oxidation number from 0 to +1. Cl₂ is an oxidant because it undergoes the decrease of oxidation number from 0 to -1.

Autoredox Reaction (Disproportionation Reaction)

Autoredox reaction is a chemical reaction in which a substance undergoes both oxidation and reduction, and acts as both oxidant and reductant result the dissimilar substances.

On the above reaction is a autoredox reaction, because Cl₂ undergoes both oxidation and reduction, and acts as both oxidant and reductant.

Electrolyte and Non Electrolyte Solutions

Definition
. Electrolyte solution is a solution which can conduct electricity.
. Non electrolyte solution is a solution which can not conduct electricity.

Why electrolyte solution can conduct electricity??
Arrhenius’s theory states “in the electrolyte solution, the dissolved chemical compound (electrolyte substance) is dissociated into ions, even when there is no current flowing through the solution”.
According to Arrhenius’s theory, electrolyte solution can conduct electricity, because in the electrolyte solution there are ions that can move freely. These ions which conduct electric currents.
Electrolyte substances if there are dissolved into water will be dissociated into ions. Meanwhile, for non electrolyte substances will no be dissociated into ions, but they are stay in the form of uncharged molecules. This case causing non electrolyte solution can not conduct electricity. The following are examples of reaction of electrolyte and non electrolyte substance in water.

• Examples of reaction of electrolyte substance in water
NaCl(s) --> Na+(aq) + Cl-(aq)
H2SO4 (l)--> 2H+(aq) + SO42-(aq)
• Examples of reaction of non electrolyte substance in water
C6H12O6(s) --> C6H12O6(aq)
CO(NH2)2(s) --> CO(NH2)2(aq)

On the electrolyte tester. Electrolyte solution shown symptoms such as gas bubbles and glowing lamp, while in non electrolyte solution doesn’t shown that symptoms.

Basic concept of Electrolyte and non electrolyte solutions

•solution

•non electrolyte solution

•Examples:

•hydrocarbon compounds

•alcohol

•ammoniak

•electrolyte solution

•strong electrolyte solution

•Examples:

•strong acid

•strong base

•salt made from strong acid and strong base

•weak electrolyte solution

•Examples:

•weak acid

•weak base

•salt make from weak acid or weak base

Sample problem

Based on the following data, which solution include in strong electrolyte, weak electrolyte, and non electrolyte solutions.

Solution	Glowing lamp	Bubble gas
A	+	+
B	+	-
C	+	-
D	-	-
E	+	+

Solution

Strong electrolyte solutions: A and E

Weak electrolyte solutions: B and C

Non electrolyte solution: D

Electrolyte intensity

Electrolyte intensity is relate to the number of ions in the solution. Electrolyte intensity is represented by a number called ionization degree (α), which mathematically can be represented by the equation as follows:

α = ni / no

Where α: ionization degree

n_i; mole of ionized substance

n_o: mole of dissolved substance

Sample problem

0,1 mole of HF is dissolved into water, so that in the solution is obtained 0.01 mole of F^- ion. Determine the ionization degree of HF solution!

Solution

0.01/0.1= 0.1
because α = 0.1, then the electrolyte substance is weak electrolyte.