NEET UG - Qualitative detection of nitrogen sulphur phosphorus and halogens, quantitative analysis and empirical molecular formula calculations Online Test (MCQ Quiz)

1. In the Lassaigne's test for the detection of nitrogen, sodium metal is fused with the organic compound. The fused mass is then extracted with water. What is the purpose of this extraction?

A) To dissolve the excess sodium metal B) To convert the fused sodium cyanide into sodium ferrocyanide C) To convert the fused sodium cyanide into sodium ferricyanide D) To convert the fused sodium cyanide into sodium thiocyanate

2. When an organic compound containing nitrogen is fused with sodium metal, sodium cyanide is formed. Sodium cyanide is then converted to sodium ferrocyanide by reacting it with:

A) Ferrous sulphate solution B) Ferric chloride solution C) Sulphuric acid D) Potassium permanganate

3. In Lassaigne's test, the formation of a Prussian blue colouration indicates the presence of which element?

A) Sulphur B) Nitrogen C) Phosphorus D) Halogens

4. Which reagent is used to test for the presence of sulphur in an organic compound using Lassaigne's test?

A) Sodium nitroprusside solution B) Ferrous sulphate solution C) Silver nitrate solution D) Lead acetate solution

5. If an organic compound containing sulphur is fused with sodium, and the aqueous extract gives a violet colour with sodium nitroprusside solution, it indicates the presence of:

A) Nitrogen B) Sulphur C) Phosphorus D) Carbon

6. In the Lassaigne's test for halogens, the organic compound is fused with sodium. The fused mass is extracted with water. Which reagent is then added to detect the presence of halogens?

A) Sodium nitroprusside solution B) Ferrous sulphate solution C) Silver nitrate solution D) Lead acetate solution

7. When an organic compound containing chlorine is fused with sodium and the extract is acidified with dilute nitric acid, addition of silver nitrate solution gives a white precipitate. This precipitate is:

A) Silver chloride B) Silver bromide C) Silver iodide D) Silver cyanide

8. A pale yellow precipitate is formed when the aqueous extract of the Lassaigne's fused mass is acidified with dilute nitric acid and treated with silver nitrate solution. This indicates the presence of:

A) Chlorine B) Bromine C) Iodine D) Sulphur

9. A yellow precipitate, insoluble in dilute ammonia but soluble in excess concentrated ammonia, is formed in the Lassaigne's test for halogens. This indicates the presence of:

A) Chlorine B) Bromine C) Iodine D) Nitrogen

10. For the detection of phosphorus in an organic compound using Lassaigne's test, the organic compound is fused with sodium. The fused mass is extracted with water and then oxidized with an oxidizing agent. Which oxidizing agent is commonly used?

A) Potassium permanganate B) Sodium peroxide C) Potassium dichromate D) Hydrogen peroxide

11. In the qualitative detection of phosphorus, after oxidation, the solution is acidified with nitric acid and ammonium molybdate is added. The formation of a canary yellow precipitate indicates the presence of phosphorus. This precipitate is:

A) Ammonium phosphate B) Ammonium phosphomolybdate C) Sodium phosphomolybdate D) Phosphoric acid

12. Which of the following tests is used to detect the presence of both nitrogen and sulphur in an organic compound simultaneously?

A) Fehling's test B) Tollens' test C) Sodium nitroprusside test D) Magnesium sulphate test

13. When an organic compound containing both nitrogen and sulphur is fused with sodium, and the aqueous extract is treated with sodium nitroprusside, a violet colour is observed. This is due to the formation of:

A) Sodium thiocyanate B) Sodium ferrothiocyanate C) Sodium ferric thiocyanate D) Sodium sulphocyanide

14. In the quantitative analysis of an organic compound, if the percentage of an element is calculated, it refers to its percentage by:

A) Volume B) Mass C) Moles D) Number of atoms

15. The Liebig's method is used for the quantitative determination of which element in an organic compound?

A) Nitrogen B) Sulphur C) Phosphorus D) Carbon and Hydrogen

16. In the Liebig's method for estimating carbon and hydrogen, the organic compound is burnt in a stream of oxygen. The products are passed through:

A) Anhydrous calcium chloride and potassium hydroxide B) Potassium hydroxide and anhydrous calcium chloride C) Potassium hydroxide and soda lime D) Anhydrous calcium chloride and soda lime

17. In Liebig's method, the increase in mass of anhydrous calcium chloride tube corresponds to the mass of:

A) Water B) Carbon dioxide C) Hydrogen D) Carbon

18. In Liebig's method, the increase in mass of potassium hydroxide solution corresponds to the mass of:

A) Water B) Carbon dioxide C) Hydrogen D) Carbon

19. The Kjedahl's method is used for the quantitative estimation of which element?

A) Sulphur B) Phosphorus C) Nitrogen D) Halogens

20. In Kjedahl's method, the organic compound is heated with concentrated sulphuric acid in the presence of:

A) Potassium sulphate and mercury or copper sulphate B) Sodium hydroxide and mercury C) Potassium dichromate and copper sulphate D) Potassium permanganate and mercury

21. In Kjedahl's method, nitrogen is converted to:

A) Ammonia B) Nitrogen gas C) Ammonium sulphate D) Nitrous oxide

22. The ammonium sulphate formed in Kjedahl's method is then distilled with:

A) Concentrated sulphuric acid B) Sodium hydroxide solution C) Hydrochloric acid D) Nitric acid

23. The liberated ammonia in Kjedahl's method is absorbed in a known excess of:

A) Sulphuric acid B) Hydrochloric acid C) Oxalic acid D) Standard acid solution (e.g., H2SO4 or HCl)

24. The excess acid remaining after absorbing ammonia in Kjedahl's method is titrated with a standard solution of:

A) Potassium hydroxide B) Sodium hydroxide C) Ammonium hydroxide D) Calcium hydroxide

25. The Carius tube method is used for the quantitative determination of halogens and sulphur. The Carius tube is made of:

A) Soft glass B) Pyrex glass C) Quartz D) Borosilicate glass

26. In the Carius method for estimating halogens, the organic compound is heated with concentrated nitric acid and:

A) Silver nitrate B) Potassium permanganate C) Sulphuric acid D) Sodium peroxide

27. The halogen in Carius method is converted to:

A) Hydrogen halide B) Silver halide C) Metal halide D) Ammonium halide

28. The precipitate of silver halide formed in Carius method is filtered, washed, dried and weighed. This precipitate is:

A) AgCl, AgBr, or AgI B) Ag2O C) AgNO3 D) Ag2SO4

29. In the Carius method for estimating sulphur, the organic compound is heated with concentrated nitric acid. The sulphur is oxidized to:

A) Sulphur dioxide B) Sulphuric acid C) Sulphurous acid D) Sulphur trioxide

30. The sulphuric acid formed in Carius method for sulphur estimation is precipitated as:

A) Barium sulphate B) Lead sulphate C) Calcium sulphate D) Sodium sulphate

31. The empirical formula of a compound represents the:

A) Actual number of atoms of each element in a molecule B) Simplest whole number ratio of atoms of each element in a molecule C) Ratio of masses of elements in a compound D) Percentage composition of elements in a compound

32. The molecular formula of a compound represents the:

A) Simplest whole number ratio of atoms of each element in a molecule B) Actual number of atoms of each element in a molecule C) Empirical formula multiplied by a factor D) Sum of atomic masses of elements

33. If the empirical formula mass of a compound is 'E' and its molecular mass is 'M', then the molecular formula is related to the empirical formula by the relation:

A) Molecular Formula = (E/M) x Empirical Formula B) Molecular Formula = (M/E) x Empirical Formula C) Molecular Formula = M x E x Empirical Formula D) Molecular Formula = M + E + Empirical Formula

34. A compound contains 40% carbon, 6.67% hydrogen and 53.33% oxygen by mass. The empirical formula of this compound is:

A) CH2O B) C2H4O2 C) C3H6O3 D) CHO

35. If the molecular mass of the compound with empirical formula CH2O is 180 g/mol, its molecular formula is:

A) CH2O B) C6H12O6 C) C2H4O2 D) C3H6O3

36. In the determination of empirical formula, the percentage composition of each element is first converted into:

A) Mass in grams B) Moles C) Number of atoms D) Volume in litres

37. After calculating the moles of each element, the next step in determining the empirical formula is to divide the mole values by the:

A) Largest mole value B) Smallest mole value C) Average mole value D) Sum of mole values

38. If the ratios obtained after dividing by the smallest mole value are not whole numbers, they are multiplied by the smallest integer that makes them:

A) Fractional B) Zero C) Whole numbers D) Negative

39. A compound has the following percentage composition: C = 75%, H = 25%. Its empirical formula is:

A) CH B) CH2 C) CH3 D) C2H3

40. If the molecular weight of a compound with empirical formula CH3 is 30 g/mol, its molecular formula is:

A) CH3 B) C2H6 C) C3H9 D) CH

41. Which of the following is NOT a quantitative method for estimating elements in organic compounds?

A) Liebig's method B) Kjedahl's method C) Carius method D) Fehling's test

42. In the detection of halogens using Lassaigne's test, if the solution is acidified with dilute H2SO4 instead of dilute HNO3 before adding AgNO3, what would be the result?

A) No precipitate would form B) A precipitate of Ag2SO4 would form C) The test would still be positive for halogens D) A precipitate of AgCN would form

43. The molar mass of an organic compound is 180 g/mol. Its elemental analysis shows C = 40%, H = 6.67%, and O = 53.33%. What is its molecular formula?

A) C6H12O6 B) CH2O C) C2H4O2 D) C3H6O3

44. In the quantitative estimation of phosphorus, if 0.2 g of an organic compound gives 0.5 g of magnesium pyrophosphate (Mg2P2O7), the percentage of phosphorus in the compound is approximately:

A) 16.5% B) 32.5% C) 45.2% D) 58.0%

45. A sample of an organic compound weighing 0.5 g, when subjected to Kjedahl's method, yielded ammonia which required 20 mL of 0.1 M H2SO4 for complete neutralisation. The percentage of nitrogen in the compound is:

A) 11.2% B) 22.4% C) 33.6% D) 44.8%

46. In the Carius method, 0.3 g of an organic compound containing chlorine gave 0.66 g of AgCl. The percentage of chlorine in the compound is approximately (Atomic mass of Ag = 108, Cl = 35.5):

A) 22.1% B) 33.2% C) 44.3% D) 55.4%

47. A compound contains C, H, and O. Its empirical formula is C3H6O. If its molecular weight is 114 g/mol, what is its molecular formula?

A) C3H6O B) C6H12O2 C) C3H6O2 D) C6H12O6

48. The fusion of organic compound with sodium metal is a preliminary step for the detection of which elements?

A) C, H, O B) N, S, Halogens C) P, S, N D) C, N, S

49. Which of the following tests is used for the quantitative estimation of sulphur in an organic compound?

A) Liebig's method B) Kjedahl's method C) Carius method D) Dumas method

Qualitative detection of nitrogen sulphur phosphorus and halogens, quantitative analysis and empirical molecular formula calculations - Online Test

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