Types of Reactions

Solubility

Salts dissolve in water to form electrolyte solutions (though some have extremely small solubility)

• < 0.01 $\frac{mol}{L}$: insoluble
• < 0.1 $\frac{mol}{L}$: slightly soluble
• else: soluble

Precipitation

Write Net Ionic Equations

1. find insoluble salt from the product
2. only this salt and its ions are participated in the reaction

Equation: MgBr₂(aq) + PbSO₄(aq) -> PbBr₂(s) + MgSO₄(aq)

Net Ionic Equation: Pb²⁺(aq) + Br^- -> PbBr₂(s)

Acid and Base Reaction

See Acid and Bases

Redox Reaction

Oxidizing agent: the atom let other atom loses electrons, has higher oxidation number

Reducing agent: the atom let other atom gains electrons

Mg(s) + Cl₂ -> Mg²⁺ + Cl^-

Reducing agent + Oxidizing agent -> "Conjugate" oxidizing agent + "Conjugate" reducing agent

Oxidation and Reduction Reaction are strongly product favoured: Mg and Cl are stronger reducing agent and oxidizing agent then Mg²⁺ and Cl^-

Oxidation Numbers

The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom.

Calculation Method 1

ON = core charge - (number of non-bonding electrons) - (number of bonding electrons in bonds to less electronegative elements)

Calculation Method 2

1. The sum of all the oxidation numbers in a species equals its charge zero for a neutral molecule.
2. Atoms in elemental form (e.g., Br₂(I), Fe(s), O₂(g)) have oxidation number zero.
3. Fluorine (the most electronegative element) has oxidation number, -1, in all of its compounds.
4. Oxygen (the next most electronegative element) has oxidation number, -2, in its compounds - except in peroxides (A-O-O-B compounds such as H₂O₂) where it has oxidation number, -1, and in F₂O where it has oxidation number, +2.
5. Chlorine, bromine and iodine have oxidation number -1, unless bonded to a more electronegative element.
6. Group 16 elements, such as Sulfur and Selenium, have oxidation number -2. unless bonded to a more electronegative element. Group 15 elements, such as Nitrogen and Phosphotus, have oxidation number -3, unless bonded to a more electronegative element.
7. Hydrogen has oxidation number, +1, when bonded to non-metals (e.g. H₂O and HN₃), except hydrogen has oxidation number, -1, in PH₃. Hydrogen has oxidation number -1 in main group metal (group I and II, Al, Ga, In, Tl, Sn, Pb and Bi) and semimetal (B, Si, Ge, As, Sb, Te and Po) hydrides.
8. Some transition metals (e.g. Au) have higher electronegativity than hydrogen, and hydrogen has oxidation +1 in the associated compound.

Balence Redox Reactions

1. balance 2 half reactions with respect to electrons

Acidic Solution

Balance the reaction using H₂O and H⁺

1. Identify the oxygen deficient side of the reaction. Add one H₂O to that side for each missing oxygen atom.
2. Identify the hydrogen deficient side of the reaction. Add one H⁺ to that side for each missing hydrogen atom.

Basic Solution

Balance the reaction using H₂O and OH^-

1. Identify the oxygen deficient side of the reaction. Add one OH⁻ to that side for each missing oxygen atom.
2. Identify the hydrogen deficient side of the reaction. Add one H₂O to that side, and one OH⁻ to the other side, for each missing hydrogen atom.

Galvanic Cell

Cathod: reduction reaction

Anode: oxidation reaction

Standard Reduction/Oxidation Potential

Standard Reduction potential (E°_red): likelihood of it will be reduced (gain electron)

Standard Oxidation Potential (E°_ox): likelihood of it will be oxidized

Reduction potential of H = 0

E°_red = electrode reduction potential - H reduction potential

E°_ox = - E°_red

Cathode should have higher E°_red

Elements with higher reduction potential can oxidize elements with lower reduction potential (e.g. F₂ + 2Cl^- -> 2f^- +Cl₂)

Standard Cell Potential

• Preasure = 1bar
• Temperature = 298K
• [Salt solution] = 1 $\frac{mol}{L}$

E°_cell = E°_red,cathode + E°_ox,anode

E°_cell > 0: reaction will proceed

E°_cell < 0: reaction will reverse

Disproportionation Reaction

A special kind of Redox reaction where oxidizing and reducing agents are the same species, and it reacts with itself.

e.g. 2H₂O₂ -> 2H₂O + O₂

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Last update: November 12, 2021
Created: September 19, 2021