Difference Between Chromate and Dichromate

Thekey differencebetween chromate and dichromate is thatchromate appears in a bright yellow colour, whereas dichromate appears in a bright orange colour.

Chromate and dichromate are阴离子containing铬and oxygen atoms. Therefore, they are oxyanions of chromium. We often use these terms as general terms to name the compounds containing these anions. These two anions have closely similar chemical structures; chromate has one chromate anion whereas dichromate has two chromate anions in combination with each other. But they have different appearances.

内容

1.Overview and Key Difference
2.What is Chromate
3.What is Dichromate
4.Side by Side Comparison – Chromate vs Dichromate in Tabular Form
5.概括

What is Chromate?

Chromate is an oxyanion of chromium having the chemical formula CrO₄^2-. Generally, we use this term to name the compounds containing this anion collectively as one group, i.e. compounds containing the chromate anion are named as chromates. Usually, the chromates have a bright yellow colour. The chromium atom in this anion is in +6oxidation state. It is a moderately strong oxidizing agent. The molar mass of this anion is 115.99 g/mol.

When considering the properties and reactions of chromates, they can react with hydrogen peroxide since the peroxide anion replaces one or more oxygen atoms. In an aqueous solution, there is usually an equilibrium between chromate and dichromate. However, we can find a high amount of chromate at high pH values (higher than 6.5 pH) where dichromate amount is very small. This means, in alkaline solutions, the predominant species is chromate.

What is Dichromate?

Dichromate is an oxyanion of chromium having the chemical formula Cr₂O₇^2-. Usually, we use this term to name the compounds containing this anion collectively as one group. For e.g., potassium dichromate, sodium dichromate are dichromates. Furthermore, the compounds containing dichromate as the anion show a bright orange colour. The molar mass of this anion is 215.99 g/mol. When considering the geometry of dichromate, it has tetrahedral geometry around the chromium atom.

在水溶液中，通常在铬酸盐和二分法之间存在平衡。However, we can find a high amount of dichromate and very small amount of chromate at low pH values (lower than 6.5 pH).

What is the Difference Between Chromate and Dichromate?

铬酸盐和二色酸盐是含有铬原子和氧原子的阴离子。因此，它们是铬的氧气。The key difference between chromate and dichromate is that chromate appears in a bright yellow colour, whereas dichromate appears in a bright orange colour. Moreover, chromate ion has one chromium atom per anion while dichromate ion has two chromium atoms per anion.

此外，镀铬酸盐和二分法之间的进一步差异是其摩尔质量。二色阴离子的摩尔质量为215.99 g/mol，而铬酸盐阴离子的摩尔质量为115.99 g/mol。在水溶液中，通常在铬酸盐和二分法之间存在平衡。但是，我们可以在高pH值（高于6.5 pH值）下找到大量的铬酸盐，其中二分法量很小。但是，在低pH值（低于6.5 pH值）下，有更多的二分法离子。

摘要 - 铬酸盐与二分法物

铬酸盐和二色酸盐是含有铬原子和氧原子的阴离子。因此，它们是铬的氧气。镀铬酸盐和二分球之间的关键区别在于，铬酸盐以鲜黄色出现，而二分酸盐以鲜艳的橙色出现。在水溶液中，通常在铬酸盐和二分法之间存在平衡。但是，我们可以在高pH值（高于6.5 pH值）下找到大量的铬酸盐，而在低pH值（低于6.5 pH）中，有更多的二分法离子。

Reference:

1.“Dichromate.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine,Available here.
2.“Potassium Dichromate.” Wikipedia, Wikimedia Foundation, 9 Nov. 2019,Available here.
3. Cheremisinoff, Paul N. “Treatment of Effluent Fertilizer Industry Example.” Waste Minimization and Cost Reduction for the Process Industries, 1995, pp. 285–324., doi:10.1016/b978-081551388-9.50010-5.

Image Courtesy:

1.本·米尔斯（Ben Mills）的“ Chomate-2D维度” - 通过Commons Wikimedia
2. “Potassium-dichromate-sample” By Benjah-bmm27 – Own work (Public Domain) viaCommons Wikimedia