Page 2: Chromium Compounds and Their Reactions

This page delves deeper into the behavior of chromium compounds in different environments and their redox properties.

Stability of chromates and dichromates:

• K₂CrO₄ is stable in basic conditions but converts to K₂Cr₂O₇ in acidic environments.
• K₂Cr₂O₇ is stable in acidic conditions but transforms to K₂CrO₄ in basic environments.

Definition: Chromates are yellow, while dichromates are orange, providing a visual indicator of the solution's pH.

Oxidizing properties of K₂Cr₂O₇:

• In acidic conditions, Cr₂O₇²⁻ is reduced to Cr³⁺, changing color from orange to green.

Reducing properties of Cr³⁺ salts:

• Cr³⁺ can be oxidized to CrO₄²⁻ in basic conditions with strong oxidizing agents like H₂O₂.

Example: The thermal decomposition of ammonium dichromate produces Cr₂O₃, nitrogen, and water, demonstrating the redox behavior of chromium compounds.

Redox reactions involving chromium compounds:

• Various substances can act as reducing agents (e.g., NO₂⁻, H₂O₂, SO₃²⁻) or oxidizing agents (e.g., MnO₄⁻, ClO⁻, O₃) in reactions with chromium compounds.

Highlight: Understanding these redox reactions is essential for solving pierwiastki bloku d zadania maturalne.

Page 1: Chromium and Its Compounds

This page focuses on the atomic structure, reactions, and oxidation states of chromium, a key element in pierwiastki bloku d.

Chromium's atomic structure is [Ar] 3d⁵4s¹, with elektrony walencyjne bloku d playing a crucial role in its chemical behavior.

Reactions of chromium:

• With non-oxidizing acids: Cr reacts with HCl to form CrCl₂ and hydrogen gas.
• With concentrated acids: Chromium undergoes pasywacja, forming a protective oxide layer.
• With bases: Cr reacts with NaOH to form sodium chromite and hydrogen gas.

Vocabulary: Pasywacja refers to the formation of a protective oxide layer on a metal surface, preventing further reaction.

Chromium's oxidation states and compounds:

• Cr(II): Forms brown precipitates with a basic character.
• Cr(III): Produces grayish-green precipitates with amphoteric properties.
• Cr(VI): Has 6 valence electrons and forms acidic compounds.

Example: Cr(OH)₃ exhibits amphoteric behavior, reacting with both acids and bases.

Key chromium compounds:

• Chromium(III) oxide (Cr₂O₃): Amphoteric in nature.
• Chromium(VI) oxide (CrO₃): Acidic character, forms chromic and dichromic acids.
• Potassium chromate (K₂CrO₄) and dichromate (K₂Cr₂O₇): Important Cr(VI) compounds.

Highlight: Understanding the various oxidation states of chromium is crucial for pierwiastki bloku d sprawdzian and zadania maturalne.