Potassium Dichromate Flashcards
What is the main industrial use of potassium dichromate (K₂Cr₂O₇)?
Potassium dichromate is used as an oxidant in leather processing and the preparation of azo compounds.
How are dichromates typically prepared?
Dichromates are obtained by the fusion of chromate ore (FeCr₂O₄) with sodium or potassium carbonate in the presence of air.
Write the reaction of chromate ore with sodium carbonate to produce sodium chromate.
4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂
What is the process to convert sodium chromate to sodium dichromate?
The yellow solution of sodium chromate is filtered and acidified with sulfuric acid to produce sodium dichromate.
Write the chemical equation for the conversion of sodium chromate to sodium dichromate.
2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + H₂O
What is the color of sodium dichromate?
Sodium dichromate is orange.
What is potassium dichromate commonly used for besides leather processing?
It is used in the preparation of azo compounds.
What is the main ore used to prepare dichromates?
Chromate ore, also known as FeCr₂O₄.
What is the role of sodium or potassium carbonate in the preparation of dichromates?
It reacts with chromate ore during the fusion process to produce chromates.
What happens to the solution of sodium chromate after acidification?
It is converted to sodium dichromate, which can then be crystallized.
Write the complete process to prepare potassium dichromate (K₂Cr₂O₇) from chromate ore.
- Chromate ore reacts with sodium carbonate and oxygen to form sodium chromate. 2. Sodium chromate is acidified with sulfuric acid to form sodium dichromate. 3. Sodium dichromate is treated with potassium chloride to produce potassium dichromate.
Why is potassium dichromate preferred over sodium dichromate in some reactions?
Potassium dichromate is less hygroscopic and more stable.
What is the chemical equation for the preparation of potassium dichromate from sodium dichromate?
Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl
What is the color of potassium dichromate?
Potassium dichromate is orange.
What type of compound is potassium dichromate?
It is an oxidizing agent.
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Why is sodium dichromate more soluble than potassium dichromate?
Sodium dichromate has higher solubility due to its ionic nature and smaller cation size compared to potassium dichromate.
What is the chemical reaction for preparing potassium dichromate from sodium dichromate?
Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl
What is the effect of pH on the interconversion of chromates and dichromates?
- Acidic medium: Dichromates are formed. - Basic medium: Chromates are formed.
Write the equation for the interconversion of chromates to dichromates in acidic medium.
2CrO₄²⁻ + 2H⁺ → Cr₂O₇²⁻ + H₂O
Write the equation for the interconversion of dichromates to chromates in basic medium.
Cr₂O₇²⁻ + 2OH⁻ → 2CrO₄²⁻ + H₂O
What happens to the color of the solution during the interconversion of chromates and dichromates?
- Chromates (CrO₄²⁻) are yellow. - Dichromates (Cr₂O₇²⁻) are orange.
What remains constant during the interconversion of chromates and dichromates?
The oxidation state of chromium remains constant at +6.
Why are dichromates and chromates strong oxidizing agents?
They readily accept electrons, reducing chromium from +6 to +3 oxidation state.
What are the chemical formulas for chromate and dichromate ions?
Chromate ion: CrO4²⁻, Dichromate ion: Cr2O7²⁻
What is the structural difference between chromate and dichromate ions?
The chromate ion is tetrahedral, while the dichromate ion consists of two tetrahedra sharing one corner with a Cr-O-Cr bond angle of 126°.
What is the reaction between dichromate and hydroxide ions?
Cr2O7²⁻ + 2OH⁻ → 2CrO4²⁻ + H2O
What are the solubility and common uses of sodium and potassium dichromates?
Sodium dichromate has greater solubility in water and is used as an oxidizing agent in organic chemistry. Potassium dichromate is used as a primary standard in volumetric analysis.
Write the reduction reaction of dichromate ion in acidic solution.
Cr2O7²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H2O (E° = 1.33V)
How does potassium dichromate oxidize iodides?
6I⁻ → 3I2 + 6e⁻
How does potassium dichromate oxidize sulfides?
3H2S → 6H⁺ + 3S + 6e⁻
How does potassium dichromate oxidize tin(II) ions?
3Sn²⁺ → 3Sn⁴⁺ + 6e⁻
How does potassium dichromate oxidize iron(II) ions?
6Fe²⁺ → 6Fe³⁺ + 6e⁻
Write the full ionic equation for the reaction of potassium dichromate with ferrous ion (Fe²⁺).
Cr2O7²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H2O
Why are dichromates strong oxidizing agents?
Because they readily accept electrons and have a high standard reduction potential (E° = 1.33V).
