Qualitative detection of N S P and halogens in organic compounds - Question Bank
1. In the Lassaigne's test for sulfur, if the sodium fusion extract is acidified with acetic acid and then treated with sodium nitroprusside, a violet color is observed. This is due to the formation of:
2. Which of the following tests is specifically designed for the detection of halogens in organic compounds and involves heating the compound with copper powder on a wire loop in a flame?
3. The Kjeldahl's method is primarily used for the quantitative estimation of:
4. When testing for halogens, if the organic compound contains iodine, the sodium fusion extract, after acidification with nitric acid and addition of silver nitrate, gives a yellow precipitate. This precipitate is:
5. The qualitative detection of phosphorus often involves converting it to phosphate. Which of the following oxidizing agents is NOT typically used in this conversion process?
6. Which of the following elements can be detected using a simple flame test with copper wire (Beilstein test)?
7. In the detection of nitrogen, the initial reaction of sodium cyanide with ferrous sulfate forms sodium ferrocyanide. Further addition of ferric chloride and acidification leads to the formation of Prussian blue. What is the chemical formula of Prussian blue?
8. If an organic compound contains only sulfur, the Lassaigne's test would yield sodium sulfide. Upon acidification with acetic acid and addition of lead acetate, a black precipitate of ____ is formed.
9. Which of the following pairs of elements and their characteristic Lassaigne's test observations is INCORRECT?
10. After oxidation of phosphorus to phosphoric acid, it can be detected by adding ammonium molybdate and observing the formation of a yellow precipitate. This is similar to the step in which other detection method?
11. The detection of phosphorus can also be carried out by heating the organic compound with concentrated sulfuric acid and potassium permanganate. This process oxidizes phosphorus to:
12. Which element's detection involves the formation of a colored complex with iron(III) chloride after oxidation?
13. In the Lassaigne's test, if the organic compound contains nitrogen and the resulting sodium fusion extract is incorrectly acidified with sulfuric acid before adding ferrous sulfate, what might be the consequence?
14. When testing for phosphorus, if the organic compound contains halogens, the presence of halogens can interfere by forming precipitates with ammonium molybdate. What precaution is taken to avoid this interference?
15. Which of the following statements is true regarding the detection of halogens using silver nitrate after sodium fusion?
16. If an organic compound contains both chlorine and bromine, and is subjected to the Lassaigne's test for halogens, what would be observed upon addition of silver nitrate?
17. In the Lassaigne's test for halogens, why is the sodium fusion extract acidified with nitric acid before adding silver nitrate?
18. Which of the following is a limitation of the Beilstein test for halogens?
19. The Beilstein test is a qualitative test for halogens. It involves heating the organic compound with copper powder. A green or blue flame indicates the presence of:
20. Which of the following precipitates formed with silver nitrate in the Lassaigne's test for halogens is insoluble in ammonium hydroxide?
21. A yellow precipitate, insoluble in ammonium hydroxide, is formed when testing for halogens using the Lassaigne's test. This indicates the presence of:
22. If the precipitate formed with silver nitrate in the Lassaigne's test for halogens is pale yellow and soluble in ammonium hydroxide, it indicates the presence of:
23. A white precipitate, insoluble in dilute nitric acid but soluble in ammonium hydroxide, is formed when testing for halogens. This indicates the presence of:
24. When silver nitrate solution is added to the sodium fusion extract (acidified with nitric acid) for halogen detection, a precipitate is formed. The color of the precipitate indicates the presence of:
25. In the Lassaigne's test for halogens, the organic compound is fused with sodium metal. The resulting mass is extracted with water, forming sodium halide. This extract is then acidified with dilute nitric acid. What is the next step to detect halogens?
26. The qualitative detection of halogens in organic compounds is most commonly done using which test?
27. Which of the following elements cannot be detected using the Lassaigne's test?
28. If the organic compound contains phosphorus and halogens, the phosphorus test might be affected. To avoid interference from halogens, which acid is typically used to acidify the aqueous extract before adding ammonium molybdate?
29. The yellow precipitate formed with ammonium molybdate in the test for phosphorus is chemically known as:
30. Which reagent is used to detect the presence of phosphate ions in the qualitative analysis of phosphorus in organic compounds?
31. After fusing the organic compound with sodium carbonate and sodium nitrate for phosphorus detection, the fused mass is extracted with water. The aqueous extract is then acidified and treated with ammonium molybdate in the presence of nitric acid. What is the characteristic observation for phosphorus?
32. In the detection of phosphorus, the organic compound is fused with sodium carbonate and an oxidizing agent like sodium nitrate. What is the resulting inorganic product containing phosphorus?
33. The detection of phosphorus in organic compounds typically involves its oxidation to phosphate. Which method is commonly used for this purpose?
34. Which reagent is used to detect sulfide ions formed in the Lassaigne's test for sulfur?
35. If an organic compound contains sulfur and is subjected to the Lassaigne's test, and the sodium fusion extract is acidified with acetic acid and then treated with sodium nitroprusside, a violet color indicates the presence of:
36. Which of the following is a characteristic observation for the detection of sulfur using the Lassaigne's test?
37. When sodium sulfide from the Lassaigne's extract is treated with lead acetate solution, what is the observation if sulfur is present?
38. In the Lassaigne's test for sulfur, the organic compound is fused with sodium metal. The resulting mass is extracted with water, forming sodium sulfide. What is the next step to detect sulfur?
39. Which method is generally employed for the qualitative detection of sulfur in organic compounds?
40. A violet color with sodium nitroprusside in the Lassaigne's test for a compound containing both N and S indicates the presence of:
41. To distinguish between the presence of nitrogen and sulfur in the Lassaigne's test when both are present, which reagent is added to the sodium fusion extract?
42. When testing for nitrogen using the Lassaigne's method, if the organic compound contains both nitrogen and sulfur, the addition of ferrous sulfate may lead to the formation of:
43. In the Lassaigne's test, if the organic compound contains both nitrogen and sulfur, what is formed upon fusion with sodium metal?
44. Which of the following is NOT a characteristic observation for the Lassaigne's test for nitrogen?
45. If the Lassaigne's extract, after treatment with ferrous sulfate and acidification with HCl, gives a green precipitate turning blue on standing, it indicates the presence of:
46. Which reagent is used to detect the presence of cyanide ions in the Lassaigne's extract when testing for nitrogen?
47. When an organic compound containing nitrogen is fused with sodium metal, and the resulting mass is extracted with water, sodium cyanide is formed. This extract is then treated with ferrous sulfate. What is the colored precipitate formed if nitrogen is present?
48. In the Lassaigne's test for nitrogen, sodium metal is fused with the organic compound in a fusion tube. What is the primary purpose of this fusion?
49. Which method is commonly used for the qualitative detection of nitrogen in organic compounds?