Intermediate Topic 679 of 1102 Inorganic Chemistry
Chromium Compounds
Chromate and dichromate ions are interconverted by pH and are strong oxidizers.
In-depth explanation of Chromium Compounds
Chromium forms two important oxyanions in aqueous chemistry: chromate, CrO4 2-, in which chromium is +6 and the solution is yellow, and dichromate, Cr2O7 2-, which is orange. Their interconversion depends on pH: in acid chromate condenses to dichromate, and in base dichromate converts back to chromate, as in 2CrO4 2- + 2H+ giving Cr2O7 2- + H2O. Dichromate is a strong oxidizing agent in acid and is used in analysis. Chromium(VI) compounds are toxic and carcinogenic, whereas chromium(III) compounds are much less hazardous. Chromium plating gives a hard, corrosion-resistant finish.
Going deeper: Chromium Compounds
Key ideas: Cr(VI) chromate (yellow) and dichromate (orange) interconvert: 2CrO4 2- + 2H+ gives Cr2O7 2- + H2O, favored in acid, reversed in base. Dichromate is an oxidant: Cr2O7 2- + 14H+ + 6e- gives 2Cr3+ + 7H2O (green), E0 +1.33 V. Ethanol oxidation by dichromate underlies the breath test. Cr2O3 is a green pigment. Cr3+ is amphoteric hydroxide, dissolves in excess NaOH.
Common mistakes and connections: Students forget that this equilibrium is not a redox reaction; Cr stays +6. Dichromate is a primary standard in titrations, unlike permanganate, since K2Cr2O7 is stable and pure. Cr(VI) is carcinogenic. Chromium plating gives hard corrosion resistant coatings. Links to redox balancing, Le Chatelier and titration.
Visualization of Chromium Compounds
Chromate/dichromate equilibrium 2CrO4 2- + 2H+ to Cr2O7 2- + H2O: adding acid shifts it to orange dichromate, adding base reverses it. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Adding acid to a yellow chromate solution turns it orange as dichromate forms.
Frequently asked questions about Chromium Compounds
What is Chromium Compounds?
Chromate and dichromate ions are interconverted by pH and are strong oxidizers.
Is Chromium Compounds a beginner, intermediate or advanced topic?
Chromium Compounds is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Chromium Compounds?
Study these earlier topics in Inorganic Chemistry first: Steel, Copper Chemistry, Zinc Chemistry.
What comes after Chromium Compounds?
The next topics in Inorganic Chemistry are Potassium Permanganate and Silver Chemistry.
Can I practise Chromium Compounds with quizzes?
Yes. The interactive lesson includes a self-check question on Chromium Compounds, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Chromium Compounds fits in Inorganic Chemistry
Chromium Compounds is topic 64 of 113 in Inorganic Chemistry.