1. Q1. When potassium dichromate is heated, what happens?
On heating potassium dichromate decomposes to form potassium chromate, chromic oxide and oxygen. Also when heated strongly it gets decomposed into a yellow coloured compound, an oxide of chromium which is green in colour as well as oxygen gas.
2. Q2. Is K2Cr2O7 a reducing agent?
Potassium dichromate is a potassium salt that is dipotassium salt of dichromic acid. It has the role as an oxidising agent.
3. Q3. In what applications does potassium dichromate find use?
Among the various applications for potassium dichromate, K2Cr2O7, as an oxidizing agent, is used most widely as a chemical reagent. As with all hexavalent chromium compounds, it is acutely and chronically toxic to fitness.
4. Q4. What is the purity of potassium dichromate?
The two chemicals, potassium dichromate, and water are combined. All portions of the sample are equivalent because potassium dichromate is uniformly dissolved in the bath. There's no doubt that it's homogenous. Pure substance consists of just one chemical compound.
5. Q5. What is the reason for the colour of potassium dichromate?
This red-orange crystal is made of potassium dichromate. Oxygen is transferred by electrons into the vacant d- orbital of the Cr6+ complex, which gives it the colour we see. Charge transfer from ligand to metal is known as a ligand to metal charge transfer (LMCT). Consequently, light and complementary colours are absorbed by electronic transfers.
6. What are the environmental concerns associated with K2Cr2O7?
K2Cr2O7 is a toxic substance and a known carcinogen. It can cause severe environmental damage if released into water bodies or soil. Proper handling and disposal are crucial to prevent contamination and protect ecosystems and human health.
7. What is the significance of K2Cr2O7 in the detection of ethanol in breath analyzers?
K2Cr2O7 is used in some types of breath analyzers to detect ethanol. The ethanol in the breath reduces the orange dichromate to green Cr^3+ ions, and the color change is measured to determine the alcohol concentration.
8. What is the role of K2Cr2O7 in the production of lead chromate pigments?
K2Cr2O7 is used in the production of lead chromate pigments, which have a bright yellow to orange-red color. These pigments are formed by reacting K2Cr2O7 with lead compounds, and they find applications in paints, inks, and plastics.
9. How does K2Cr2O7 interact with sulfur-containing compounds?
K2Cr2O7 can oxidize many sulfur-containing compounds. For example, it can oxidize sulfides to sulfates, a reaction that is used in qualitative analysis and in some industrial processes for sulfur removal.
10. What is the role of K2Cr2O7 in the determination of alcohol content in biological samples?
K2Cr2O7 is used in some methods for determining alcohol content in biological samples. The dichromate oxidizes the alcohol, and the extent of the reaction (measured by the color change) is used to quantify the alcohol concentration.
11. How does K2Cr2O7 behave differently from K2CrO4 in solution?
In solution, K2Cr2O7 (dichromate) exists in equilibrium with CrO4^2- (chromate) ions. In acidic conditions, the equilibrium shifts towards dichromate (orange), while in basic conditions, it shifts towards chromate (yellow). K2CrO4, on the other hand, exists primarily as chromate ions in solution.
12. What is the significance of K2Cr2O7 in qualitative analysis?
In qualitative analysis, K2Cr2O7 is used to detect the presence of certain ions or functional groups. For example, it can be used to test for the presence of sulfide ions (which reduce dichromate to a green Cr^3+ solution) or to distinguish between primary, secondary, and tertiary alcohols based on their oxidation rates.
13. How does the solubility of K2Cr2O7 compare to other potassium salts?
K2Cr2O7 is moderately soluble in water (about 13g/100mL at room temperature), which is less soluble than many other potassium salts like KCl or KNO3. This property is useful in purification processes and in controlling the concentration of dichromate ions in solution.
14. What is the role of K2Cr2O7 in the production of safety matches?
K2Cr2O7 is used in the production of safety matches as an oxidizing agent in the match head composition. It helps to initiate and sustain the combustion process when the match is struck against the striking surface.
15. How does K2Cr2O7 interact with reducing agents?
When K2Cr2O7 interacts with reducing agents, it is reduced to Cr^3+ ions, typically changing color from orange to green. This reaction is often accompanied by a change in pH, as H+ ions are consumed in acidic conditions.
16. Why is K2Cr2O7 called a dichromate?
K2Cr2O7 is called a dichromate because it contains two chromium atoms in its anion (Cr2O7^2-). The prefix "di-" means two, referring to the two chromium atoms present in the compound.
17. How does the structure of K2Cr2O7 differ in solid state compared to in solution?
In the solid state, K2Cr2O7 exists as discrete K+ and Cr2O7^2- ions in a crystal lattice. In solution, especially acidic solutions, it can exist in equilibrium with other species like HCrO4- and Cr2O7^2-, depending on the pH and concentration.
18. What is the significance of K2Cr2O7 in the chrome alum synthesis?
K2Cr2O7 is a key reagent in the synthesis of chrome alum (KCr(SO4)2·12H2O). The dichromate is reduced to Cr^3+ using a reducing agent like ethanol, and then combined with sulfuric acid and potassium sulfate to form the distinctive purple chrome alum crystals.
19. What is the impact of temperature on the equilibrium between chromate and dichromate ions?
Temperature affects the equilibrium between chromate and dichromate ions. Generally, higher temperatures favor the formation of chromate ions (CrO4^2-), while lower temperatures favor dichromate ions (Cr2O7^2-). This is because the conversion of dichromate to chromate is an endothermic process.
20. What is the oxidation state of chromium in K2Cr2O7?
The oxidation state of chromium in K2Cr2O7 is +6. This high oxidation state contributes to the strong oxidizing properties of potassium dichromate.
21. How does the structure of K2Cr2O7 contribute to its properties?
The structure of K2Cr2O7 consists of two tetrahedral CrO4 units sharing an oxygen atom, forming a bent Cr-O-Cr bridge. This structure, along with the high oxidation state of chromium, contributes to its strong oxidizing properties and its ability to form intense orange-red solutions.
22. Why is K2Cr2O7 considered a strong oxidizing agent?
K2Cr2O7 is a strong oxidizing agent due to the high oxidation state (+6) of chromium and its ability to readily accept electrons. This property allows it to oxidize many other substances, making it useful in various chemical reactions and analytical processes.
23. How does the color of K2Cr2O7 change in acidic and basic solutions?
In acidic solutions, K2Cr2O7 appears orange, while in basic solutions, it turns yellow. This color change is due to the formation of different chromium species (dichromate in acidic and chromate in basic conditions) and is often used as an indicator in acid-base titrations.
24. What is the difference between chromate and dichromate ions?
Chromate ions (CrO4^2-) have a tetrahedral structure and are yellow in color, while dichromate ions (Cr2O7^2-) have two tetrahedra sharing an oxygen atom and are orange-red. Chromates are stable in basic solutions, while dichromates are stable in acidic solutions.
25. What is the role of K2Cr2O7 in chromium plating?
In chromium plating, K2Cr2O7 is used as a source of chromium ions. The dichromate ions are reduced to Cr^3+ and then further to Cr metal, which is deposited on the surface being plated, providing a hard, corrosion-resistant coating.
26. Why is K2Cr2O7 used in leather tanning?
K2Cr2O7 is used in leather tanning because it can cross-link collagen fibers in animal hides, making the leather more durable and resistant to decay. The Cr^3+ ions formed during the process bind to the collagen, stabilizing the protein structure.
27. How does K2Cr2O7 act as a primary standard in volumetric analysis?
K2Cr2O7 acts as a primary standard in volumetric analysis due to its high purity, stability, and known exact composition. It doesn't absorb moisture from the air and can be easily dried, making it ideal for preparing standard solutions of known concentration for titrations.
28. How does K2Cr2O7 react with organic compounds?
K2Cr2O7 can oxidize many organic compounds, often converting alcohols to aldehydes or ketones, and further to carboxylic acids. This property is used in organic synthesis and in testing for the presence of certain functional groups.
29. How does K2Cr2O7 act as a catalyst in certain reactions?
K2Cr2O7 can act as a catalyst in certain oxidation reactions by providing a pathway for electron transfer. It can temporarily accept electrons from the reactant and then transfer them to the oxidizing agent, facilitating the overall reaction without being consumed itself.
30. What is the chemical formula of potassium dichromate?
The chemical formula of potassium dichromate is K2Cr2O7. It consists of two potassium ions (K+) and one dichromate ion (Cr2O7^2-).
31. What is the significance of K2Cr2O7 in redox titrations?
K2Cr2O7 is widely used in redox titrations due to its strong oxidizing properties and its ability to act as its own indicator. The sharp color change from orange to green at the endpoint makes it useful for determining the concentration of reducing agents in solution.
32. How does K2Cr2O7 behave as a photosensitive compound?
K2Cr2O7 is photosensitive, meaning it can undergo chemical changes when exposed to light. When mixed with organic materials and exposed to light, it can cause cross-linking reactions. This property is utilized in photoresist technology and in some early photographic processes.
33. What is the role of K2Cr2O7 in the production of chromic acid?
K2Cr2O7 is used to produce chromic acid (H2CrO4) by reacting it with concentrated sulfuric acid. This reaction is important in various industrial processes and in the preparation of other chromium compounds.
34. How does K2Cr2O7 contribute to the determination of Chemical Oxygen Demand (COD)?
K2Cr2O7 is used in the determination of Chemical Oxygen Demand (COD) in water and wastewater analysis. It oxidizes organic matter in the sample, and the amount of K2Cr2O7 consumed is used to calculate the oxygen equivalent of the organic matter, indicating the level of pollution.
35. How does K2Cr2O7 interact with halide ions?
K2Cr2O7 can oxidize halide ions (except fluoride) to their elemental form. For example, it can oxidize chloride ions to chlorine gas in the presence of acid. This reaction is used in the qualitative analysis of halides and in some industrial processes.
36. What is the role of K2Cr2O7 in the production of chromyl chloride?
K2Cr2O7 is used to produce chromyl chloride (CrO2Cl2) by reacting it with concentrated hydrochloric acid. This volatile red liquid is an important intermediate in the production of various chromium compounds and in some organic syntheses.
37. How does K2Cr2O7 behave as an analytical reagent in gravimetric analysis?
In gravimetric analysis, K2Cr2O7 can be used to precipitate certain metal ions as their chromate or dichromate salts. The precipitate is then filtered, dried, and weighed to determine the amount of the metal in the original sample.
38. How does K2Cr2O7 contribute to the passivation of metals?
K2Cr2O7 can be used in the passivation of metals, particularly stainless steel. It oxidizes the metal surface, forming a thin, protective oxide layer that enhances corrosion resistance.
39. How does K2Cr2O7 behave in a disproportionation reaction?
K2Cr2O7 can undergo disproportionation in strongly basic conditions. The Cr^6+ in dichromate can be converted to Cr^3+ and Cr^5+ species, although this is less common than its typical redox reactions.
40. What is the significance of K2Cr2O7 in the production of chromium dioxide?
K2Cr2O7 is used as a starting material in the production of chromium dioxide (CrO2), a ferromagnetic compound used in magnetic tape and other magnetic recording media. The process involves the thermal decomposition of K2Cr2O7 under specific conditions.
41. How does K2Cr2O7 contribute to the synthesis of chromium trioxide?
K2Cr2O7 is used in the production of chromium trioxide (CrO3) by reacting it with concentrated sulfuric acid. This reaction is important in the preparation of various chromium compounds and in some industrial oxidation processes.
42. What is the significance of K2Cr2O7 in the detection of unsaturation in organic compounds?
K2Cr2O7 can be used to detect unsaturation in organic compounds. When added to an organic compound containing double or triple bonds, it is reduced, changing color from orange to green. This test is particularly useful for distinguishing between saturated and unsaturated hydrocarbons.
43. How does K2Cr2O7 behave in photochemical reactions?
K2Cr2O7 can participate in photochemical reactions when exposed to light, especially UV light. This property is utilized in photoresist technology, where K2Cr2O7 mixed with organic compounds can undergo light-induced polymerization or cross-linking reactions.
44. What is the role of K2Cr2O7 in the production of chromium(III) oxide?
K2Cr2O7 can be used to produce chromium(III) oxide (Cr2O3) through thermal decomposition. This green compound is used as a pigment and as a precursor for other chromium compounds.
45. How does K2Cr2O7 interact with transition metal ions in solution?
K2Cr2O7 can form complex ions with various transition metal ions in solution. These complexes often have characteristic colors and can be used in qualitative analysis and in some spectrophotometric determinations.
46. What is the significance of K2Cr2O7 in the production of chromium sulfate?
K2Cr2O7 is used in the production of chromium sulfate by reacting it with sulfuric acid and a reducing agent. Chromium sulfate is an important compound in leather tanning and in the production of other chromium compounds.
47. How does K2Cr2O7 contribute to the detection of aldehydes and ketones?
K2Cr2O7 can be used to distinguish between aldehydes and ketones. Aldehydes are typically oxidized more readily than ketones, resulting in a more rapid color change from orange to green when treated with acidified K2Cr2O7 solution.
48. What is the role of K2Cr2O7 in the production of chromium acetate?
K2Cr2O7 can be used to produce chromium acetate by reacting it with acetic acid and a reducing agent. Chromium acetate is used in textile dyeing and as a catalyst in some organic reactions.
49. How does K2Cr2O7 behave in solid-state reactions?
In solid-state reactions, K2Cr2O7 can act as an oxidizing agent and a source of chromium. These reactions are often used in the synthesis of complex oxide materials, such as mixed metal chromates or chromium-containing ceramics.
50. What is the significance of K2Cr2O7 in the detection of reducing sugars?
K2Cr2O7 can be used to detect reducing sugars. When a reducing sugar is heated with an acidified K2Cr2O7 solution, the sugar is oxidized and the dichromate is reduced, resulting in a color change from orange to green.
51. How does K2Cr2O7 contribute to the synthesis of chromium nitrate?
K2Cr2O7 can be used to produce chromium nitrate by reacting it with nitric acid and a reducing agent. Chromium nitrate is used in leather tanning, as a mordant in dyeing, and in the production of other chromium compounds.
52. What is the role of K2Cr2O7 in the production of chromium carbide?
K2Cr2O7 can be used as a source of chromium in
