The key difference between chromic acid and chromium trioxide is that chromic acid is a strongly acidic solution that is made by combining concentrated sulfuric acid with dichromate, whereas chromium trioxide is the acidic anhydride of chromic acid.
Chromic acid and chromium trioxide are two related substances; chromic acid can be made from the hydration of chromium trioxide. These are inorganic substances containing chromium chemical element.
CONTENTS
1. Overview and Key Difference
2. What is Chromic Acid
3. What is Chromium Trioxide
4. Side by Side Comparison – Chromic Acid vs Chromium Trioxide in Tabular Form
5. Summary
What is Chromic Acid?
Chromic acid is a strongly acidic solution containing H2CrO4 molecules. However, this acid is usually prepared from the combination of concentrated sulfuric acid and dichromate. Therefore, this acid may contain a variety of compounds, including solid chromium trioxide. This strong acid is useful in cleaning glass material. The chromium atom in the molecular chromic acid is in the +6 oxidation state. This acid is considered as a strong and highly corrosive acid.
Generally, chromic acid can be observed as dark red crystals. The molecular chromic acid has common features with sulfuric acid molecules. They have similar deprotonation patterns and acidic strengths.
Chromic acid is an important oxidizing agent, and it can oxidize organic compounds such as alcohols to carboxylic acids and ketones, primary and secondary alcohols into corresponding aldehydes and ketones, etc.
Figure 01: Chromic Acid
When considering the uses of this strong acid, it is important as an intermediate in the chromium plating process, useful in ceramic glaze and coloured glass, as a powerful oxidizing agent, useful in cleaning laboratory glassware, in the musical instrument repair industry due to its ability to brighten brass material, useful in manufacturing hair dyes, as a bleach in black and white photographic reversal processing, etc.
What is Chromium Trioxide?
Chromium trioxide is an inorganic compound having the chemical formula CrO3. It is the acidic anhydrous form of chromic acid. Therefore, both these substances are sometimes available in the market under the same name. We can observe this substance as a dark, purple-coloured solid under its anhydrous condition, and when the substance is hydrated, it appears in orange colour. This substance is prepared mainly for electroplating processes. Moreover, chromium trioxide is a very powerful oxidizer; hence, it is also a carcinogen.
Figure 02: Wet Chromium Trioxide
In addition to the chrome plating process, there are other uses of chromium trioxide such as the generation of passivated chromate films that are resistant to corrosion, useful in the production of synthetic rubies, useful in applying types of anodic coating to aluminum, etc.
What is the Difference Between Chromic Acid and Chromium Trioxide?
Chromic acid is a strongly acidic solution containing H2CrO4 molecules. Chromium trioxide is an inorganic compound having the chemical formula CrO3. Chromic acid and chromium trioxide are inorganic compounds. The key difference between chromic acid and chromium trioxide is that chromic acid is a strongly acidic solution that is made by combining concentrated sulfuric acid with dichromate, whereas chromium trioxide is the acidic anhydride of chromic acid.
Below infographic lists more differences between chromic acid and chromium trioxide.
Summary – Chromic Acid vs Chromium Trioxide
Chromic can be prepared by the hydration of chromium trioxide. The key difference between chromic acid and chromium trioxide is that chromic acid is a strongly acidic solution that is made by combining concentrated sulfuric acid with dichromate, whereas chromium trioxide is the acidic anhydride of chromic acid.
Reference:
1. “Oxidation by Chromic Acid.” Chemistry LibreTexts, 13 Sept. 2020, Available here.
Image Courtesy:
1. “Chromic-Acid-Photo” By Himstakan – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Reaction between potassium dichromate and sulfuric acid (1)”By Rando Tuvikene – Own work (CC BY-SA 4.0) via Commons Wikimedia