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Dichromate is an anion and its chemical formula is Cr2O72-. This compound acts as a strong oxidizing agent and is also primarily used as the standard solution for volumetric analysis. In aqueous solutions these dichromate ions are interconvertible. Potassium Dichromate is one of the most common examples of Dichromates.
Potassium dichromate is an orange crystalline solid that gives chromic oxide and potassium chromate when it readily decomposes. Dichromate’s molecular formula is Cr2O72- and its density is 2.68 grams per centimetre cube. The molecular weight weighs 294.185 g/mol over molar mass. This compound also has a boiling point of 500 C and it also has a melting point of 398 C.
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Keyterms: Dichromate, Anion, Oxidizing agent, Solution, Aqueous solution, Chromic oxide, Crystalline solid, Potassium chromate
What is Dichromate?
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Dichromate is an anion with the chemical formula Cr2O72-. It is a strong oxidizing agent in organic chemistry and is used as a primary standard solution in volumetric analysis. Chromate and Dichromate ions are inconvertible in aqueous solutions.
| Cr2O72- | Dichromate |
|---|---|
| Density | 2.68 g/cm³ |
| Molecular Weight/ Molar Mass | 294.185 g/mol |
| Boiling Point | 500 °C |
| Melting Point | 398 °C |
| Chemical Formula | Cr2O72- |
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Dichromate: Structure
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The structure of the dichromate ion is shown in the following diagrams.
Physical Properties of Dichromate
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- It is odourless.
- Its Appearance is a Red-orange crystalline solid.
- Its Valency is 2.
- Its pH level is 4.
- Its Oxidation state is +6.
- It is appreciably soluble in hot water and moderately in cold water.
Chemical Properties of Dichromate
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- A deep blue colour with peroxide due to the formation of [CrO(O2)2] is formed when an acidified solution of Dichromate.
Cr2O72- + 4H2O2 + 2H+ → 2CrO5 + 5H2O
- It reacts with hydrogen sulphide and oxidises it to sulphur
- It oxidises sulphites to sulphates.
- It oxidises chlorides to chlorine.
- It oxidises nitrites to nitrates.
- It oxidises thiosulphates to sulphates.
- It oxidises sulphur to stannic salts.
Cr2O72- + 3H2S + 8H+ → 2Cr3+ + 3S + 7H2O
Uses of Dichromate
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There are various uses of Dichromate, some of these uses are listed below:
- It is for the hardening of gelatin film in photography.
- It is used in the leather industry for chrome tanning.
- It is also used as a mordant in dyeing fixatives like Cr(OH)3.
- It is used in the volumetric estimation of iodine, sulphite and ferrous salts.
- It is used for the preparation of compounds containing chromium such as chrome yellow, chrome red and chrome alum.
- It is used for chrome plating which helps in protecting metals from corroding and improves the adhesion of paint.
- The heavy metal, alkaline earth and lanthanide salts of Dichromate are used as pigments.
Things To Remember
- The use of lead-containing pigment chrome yellow stopped due to environmental regulations.
- Dichromate is an anion and its chemical formula is Cr2O72-. This compound acts as a strong oxidizing agent and is also primarily used as the standard solution for volumetric analysis.
- In aqueous solutions these dichromate ions are interconvertible. Potassium Dichromate is one of the most common examples of Dichromates.
- Potassium dichromate is an orange crystalline solid that gives chromic oxide and potassium chromate when it readily decomposes. Dichromate’s molecular formula is Cr2O72- and its density is 2.68 grams per centimetre cube.
- The molecular weight weighs 294.185 g/mol over molar mass. This compound also has a boiling point of 500 C and it also has a melting point of 398 C.
Also Read:
Sample Questions
Ques: How do I prepare a 0.1 N potassium dichromate solution? (4 marks)
Ans: Normality = (mass of solute x 1000) ÷ (mass of solute equivalent to grams x volume of solution (ml)).
Molar mass in grams KCr2O7 = 294.18 grams.
To find the equivalent of potassium dichromate, it is necessary to examine the changes in the oxidation state of Cr in the reactants and products, and in the acidic medium. (Cr2O72- → 2Cr3). Here, the oxidation state changed (the change was 6 because it changed from 2 × 6 to 2 × 3) to the equivalent of KCr2O7 = 294.18 / 6 = 49.03.
To prepare one regular solution, one gram of KCr2O7, or 49.03 grams, must be dissolved in one litre of solution.
To prepare a regular solution of 0.1, dissolve 4.903 grams in water to make 1 litre of solution.
Ques: How do I calculate the equivalent weight of potassium dichromate? (3 marks)
Ans: The potassium dichromate in an acid medium is a strong oxidant. This means that electrons earn during the redox reaction. The potassium dichromate in acid solution leads to: KCr2O7 14H 6E- → 2K 2CR3 7H2O equivalent weight of KCr2O7 = 294.26 / 6 = 49
Ques: What happens to chromium hybridization with dichromate ion (Cr2O72-)? (3 marks)
Ans: Cr2O72- is a special compound.
The oxidation state of Cr is 6.
There are no electrons in the Cr 6 valence shell. That is, there are empty 4s and 3d subshells. Three 3D orbitals, ie. 3dxy, 3dyz, 3dzx, and One4s orbits are used.
If you're wondering why you can't see the other d-orbitals, it's because they're in high energy levels (CFT theory) and easy to link to them.
Therefore, this results in hybridization d3.
Ques: What are the uses of dichromate compounds? (2 marks)
Ans: Dichromate compounds have many uses. They are used as oxidants and are also used in the preparation of various elements such as waxes, paints and adhesives. However, because potassium dichromate is a hexavalent chromium product, it is carcinogenic and highly toxic.
Ques: What is the dichromate test? (2 marks)
Ans: Potassium dichromate paper can be used to look for sulfur dioxide as it clearly changes from orange to white. This is typical of all redox reactions in which hexavalent chromium is reduced to trivalent chromium.
Ques: Is Sodium Dichromate an Oxidizer? (2 marks)
Ans: Sodium dichromate is a very powerful oxidant. Sodium dichromate in sulfuric acid is used to oxidize primary alcohols but is severely restricted to the corresponding acid by peroxidation with hydrated aldehydes.
Ques: Why doesn't potassium dichromate act as a self-indicating drug? (2 marks)
Ans: Cr2O7 is orange and the first drop must be yellow, so it is supposed to be used as a self-index, but Cr is 3 ((reduced form of Cr2O7))'green, so yellow is visible. not. This makes it difficult to display and visualize. Ind should be used as diphenylamine sulfonic acid as it was detected.
Ques: What is the use of potassium dichromate? (2 marks)
Ans: Potassium dichromate has a wide range of uses as an oxidizer in many chemical and industrial applications, as well as in leather colour, colour and tanning. It is also used medically as an external disinfectant or astringent.
Ques: What happens if I add potassium dichromate to hydrochloric acid? (3 marks)
Ans: Potassium dichromate is a powerful oxidant and is strong enough to oxidize HCl to Cl2 (chlorine gas; hopefully this experiment was done in succession). In this reaction, Cr2O7 (2-) dichromate, which has an oxidation number of Cr 6, is reduced to Cr (3). The half-reaction equation is:
2Cl- → Cl22 e-
Cr2O72- 6 e-14H → 2Cr37H2O
The combination of these gives a reaction equation.
6 Cl- Cr2O72- 14H → 3 Cl2 2Cr37H2O.
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