Page 2: Chromium and Manganese

This page delves into the chemistry of chromium and manganese, focusing on their various oxidation states and important reactions.

Chromium exhibits multiple oxidation states, with +3 and +6 being the most common. Chromium(III) compounds, such as Cr₂O₃ and Cr(OH)₃, display amphoteric properties.

Highlight: Chromium(VI) compounds, like chromates (CrO₄²⁻) and dichromates (Cr₂O₇²⁻), are strong oxidizing agents.

The page outlines several key reactions involving chromium compounds:

1. Formation of chromium(III) hydroxide
2. Amphoteric behavior of Cr(OH)₃
3. Thermal decomposition of ammonium dichromate

Example: (NH₄)₂Cr₂O₇ → Cr₂O₃ + N₂ + 4H₂O (decomposition of ammonium dichromate)

Manganese is presented with its various oxidation states, ranging from +2 to +7. The stability and acid-base properties of manganese compounds vary with the oxidation state.

Vocabulary: Redox - A type of chemical reaction involving the transfer of electrons between species.

Important reactions of manganese compounds are discussed, including:

1. Disproportionation of potassium permanganate
2. Amphoteric behavior of MnO₂
3. Reaction of MnO₂ with hydrogen peroxide

Example: 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂ (disproportionation of potassium permanganate)

Page 3: Iron, Hydrogen, Aluminum, and Silicon

This page covers the chemistry of iron, hydrogen, aluminum, and silicon, focusing on their properties, reactions, and applications.

Iron undergoes passivation when exposed to concentrated nitric or sulfuric acid, forming a protective oxide layer. The page outlines important reactions of iron, including its reaction with hydrochloric acid and chlorine.

Vocabulary: Passivation - The formation of a protective layer on a metal's surface, preventing further corrosion.

Hydrogen production methods are discussed, including:

1. Reaction of active metals with acids
2. Steam reforming of methane
3. Water-gas shift reaction
4. Electrolysis of water or brine

Example: CH₄ + H₂O → CO + 3H₂ (steam reforming of methane)

Aluminum's passivation and its amphoteric nature are explored. The aluminothermic reaction, used in welding, is also mentioned.

Highlight: Aluminum forms a protective oxide layer (Al₂O₃) when exposed to air, preventing further corrosion.

Silicon, an important element in the earth's crust, is discussed in terms of its inorganic compounds. Silicon dioxide (SiO₂) exhibits weak acidic properties and reacts with hydrofluoric acid.

Example: SiO₂ + 4HF → SiF₄ + 2H₂O (reaction of silicon dioxide with hydrofluoric acid)

The page concludes with a brief mention of silicic acid (H₂SiO₃) and its properties.