Qualitative & Quantitative Analysis — Practice Questions

Free NEET Chemistry multiple-choice questions on Qualitative & Quantitative Analysis. Attempt each question and reveal the answer with a full explanation.

In Lassaigne's test for the detection of nitrogen, the Prussian blue color is due to the formation of which compound? Fe 4[Fe(CN) 6] 3 Fe 3[Fe(CN) 6] 2 Na 4[Fe(CN) 6] Fe(SCN) 3 In the detection of sulfur using the Lassaigne's test, which reagent gives a black precipitate if sulfur is present? Lead acetate Sodium nitroprusside Silver nitrate Ferric chloride In the Lassaigne's test for nitrogen, the sodium fusion extract is boiled with FeSO 4 . The intermediate formed before the addition of FeCl 3 and HCl is: Sodium hexacyanoferrate(II) Sodium hexacyanoferrate(III) Ferric hydroxide Sodium thiocyanate In Kjeldahl's method, the ammonia evolved is absorbed in excess standard H 2SO 4 . The amount of ammonia is then determined by: Titrating the unreacted H 2SO 4 with a standard NaOH solution Titrating the NH 4OH directly with HCl Measuring the volume of NH 3 gas in a nitrometer Precipitating the nitrogen as AgCN In the Dumas method, the primary purpose of using CO 2 gas is to: Drive out all the air from the combustion tube Oxidize the organic compound React with nitrogen to form NO 2 Cool the nitrometer In the Schütze-Aluise method for the direct estimation of oxygen, the iodine produced is typically titrated against which reagent? Sodium thiosulfate Potassium permanganate Sodium hydroxide Silver nitrate Which of the following compounds will not give a positive Beilstein test? Fluorobenzene Chlorobenzene Bromobenzene Iodobenzene In the Carius method, 0.20 g of an organic compound gave 0.287 g of AgCl . What is the percentage of chlorine in the compound? (Atomic mass: Ag=108, Cl=35.5 ) 35.5% 25.0% 71.0% 14.35% Which of the following statements is incorrect regarding the use of sodium fusion extract in Lassaigne's test? K is used instead of Na because it reacts more vigorously and yields better results The extract is boiled with HNO 3 to decompose CN - and S 2- ions before testing for halogens A blood-red color with FeCl 3 indicates the presence of both N and S The extract must be alkaline for the detection of nitrogen In the detection of nitrogen by Lassaigne's test, if the sodium fusion extract contains sulfur as well, what modification is observed in the color test? A blood-red color is observed with FeCl 3 instead of Prussian blue if Na is insufficient Prussian blue color is never formed A black precipitate is formed with FeSO 4 A violet color is formed with FeCl 3 In the Liebig method for estimation of carbon and hydrogen, 0.30 g of an organic compound on combustion gave 0.44 g of CO 2 and 0.18 g of H 2O . The percentages of C and H are: C: 40%, H: 6.67% C: 60%, H: 10% C: 30%, H: 3.33% C: 12%, H: 2% In the Duma's method, the volume of Nitrogen ( V 1 ) collected at P 1 pressure and T 1 temperature is converted to S.T.P. volume ( V 0 ). If the atmospheric pressure is P , the aqueous tension is f , and the volume is V , the corrected pressure P 1 is: P - f P + f f - P P A compound with the empirical formula CH 2O has a molecular mass of 180 g/mol. What is its molecular formula? C 6H 12 O 6 C 3H 6O 3 C 4H 8O 4 C 5H 10 O 5 In the Schütze method, the carbon monoxide ( CO ) produced from the oxygen in the compound is converted to CO 2 using which reagent? Iodine pentoxide ( I 2O 5 ) Potassium dichromate Lead dioxide Copper oxide In the Liebig's method for estimation of carbon and hydrogen, if the organic compound contains nitrogen, the oxides of nitrogen produced are removed by passing them over: Heated copper gauze Magnesium perchlorate Potassium hydroxide solution Anhydrous calcium chloride What is the empirical formula of a hydrocarbon which contains 10.5 g of carbon per gram of hydrogen? C 7H 8 C 3H 4 C 2H 2 CH 4 In the Lassaigne's test for the detection of nitrogen, if the sodium extract is not boiled with ferrous sulfate before adding ferric chloride and HCl , what might happen? The formation of Prussian blue will be hindered or fail The sulfur test will interfere with the nitrogen test The solution will turn red instead of blue The sodium cyanide will decompose into nitrogen gas In the Lassaigne's test for halogens, AgF is not precipitated even if fluorine is present in the organic compound because: AgF is highly soluble in water Fluorine does not react with sodium metal Sodium fluoride is volatile and evaporates during fusion The test requires the presence of HNO 3 , which decomposes NaF In the Kjeldahl method, selenium (Se) or a selenium compound is sometimes added during the digestion process. What is its role? As a catalyst to speed up the conversion of organic nitrogen to (NH 4) 2SO 4 To increase the boiling point of concentrated H 2SO 4 To prevent the bumping of the liquid in the Kjeldahl flask To indicate the completion of the reaction by a color change An organic compound contains 40 % Carbon and 6.7 % Hydrogen. If the remaining is oxygen and the vapor density is 30 , what is its molecular formula? C 2H 4O 2 CH 2O C 3H 6O 3 C 2H 6O In the Duma's method, the volume of nitrogen gas is measured at a certain pressure and temperature. If the level of the KOH solution inside the nitrometer is higher than the level in the reservoir, the pressure of the nitrogen gas is: Lower than the atmospheric pressure Higher than the atmospheric pressure Equal to the atmospheric pressure Equal to the aqueous tension of water In the Carius method for the estimation of chlorine, 0.30 g of an organic compound yielded 0.574 g of AgCl . What is the percentage of chlorine? (Atomic mass: Ag=108, Cl=35.5 ) 47.33 % 35.50 % 25.25 % 55.10 % In the Lassaigne's test for nitrogen, the color of the final complex (Prussian blue) is chemically identified as: Fe 4[Fe(CN) 6] 3 Fe 3[Fe(CN) 6] 2 Na 4[Fe(CN) 5NOS] Fe(SCN) 3 What is the function of anhydrous calcium chloride in the Liebig's combustion tube apparatus? To absorb water vapor produced To absorb carbon dioxide produced To remove nitrogen oxides To catalyze the oxidation of the compound If an organic compound containing C, H, N, S is fused with sodium metal, which ions will be present in the sodium fusion extract? CN -, S 2- , CNS - NH 2 -, SO 4 2- , Cl - NO 3 -, S 2- , Na + CO 3 2- , NH 4 +, S 2- In the Carius method of estimation of halogens, 0.15 g of an organic compound gave 0.12 g of AgBr . What is the percentage of bromine in the compound? (Atomic mass: Ag = 108 , Br = 80 ) 34.04 % 40.12 % 25.21 % 48.00 % In the estimation of sulfur by the Carius method, 0.468 g of an organic compound afforded 0.668 g of barium sulfate ( BaSO 4 ). What is the percentage of sulfur in the compound? 19.60 % 25.30 % 10.50 % 32.10 % In the Dumas method, 0.3 g of an organic compound gave 50 mL of nitrogen collected at 300 K and 715 mm pressure. If the aqueous tension at 300 K is 15 mm, the percentage of nitrogen is: 17.46 % 15.00 % 20.12 % 10.55 % In the Carius method, 0.235 g of an organic compound gave 0.470 g of AgI . What is the percentage of iodine in the compound? (Atomic mass of Ag = 108 , I = 127 ) 108.08 % 54.04 % 27.02 % 13.51 % The sulfur in an organic compound is converted to sodium sulfide during Lassaigne's fusion. When this extract is treated with sodium nitroprusside, a violet color is observed. The violet color is due to: [Fe(CN) 5NOS] 4- [Fe(CN) 6] 4- [Fe(CN) 5S] 3- Na 2[Fe(CN) 5NO] When nitrogen is detected in Lassaigne's test, the intermediate sodium cyanide ( NaCN ) reacts with freshly prepared ferrous sulfate ( FeSO 4 ) and ferric ions to form Prussian blue. What is the IUPAC name or formula of this Prussian blue complex? Iron(III) hexacyanoferrate(II) Iron(II) hexacyanoferrate(III) Sodium ferrocyanide Sodium ferricyanide In the quantitative estimation of phosphorus, phosphorus is precipitated as magnesium ammonium phosphate ( MgNH 4PO 4 ). On ignition, this precipitate yields which compound for weighing? Magnesium pyrophosphate ( Mg 2P 2O 7 ) Magnesium oxide ( MgO ) Phosphorus pentoxide ( P 2O 5 ) Magnesium phosphate ( Mg 3(PO 4) 2 ) In the estimation of carbon, 0.2472 g of an organic compound gave 0.4950 g of CO 2 . The percentage of carbon in the compound is approximately: 54.54 % 27.27 % 12.12 % 40.00 % In the silver salt method for determining the molecular mass of an organic acid, 0.5 g of the silver salt of a dibasic acid left 0.324 g of silver on ignition. The molecular mass of the acid is: (Atomic mass of Ag = 108 ) 126 g/mol 150 g/mol 210 g/mol 90 g/mol In the Liebig's method, the percentage of hydrogen in an organic compound is calculated from the mass of water produced using the formula: 2 18 mass of H 2O mass of compound 100 1 18 mass of H 2O mass of compound 100 18 2 mass of H 2O mass of compound 100 2 44 mass of H 2O mass of compound 100 In the estimation of nitrogen by Kjeldahl's method, 0.5 g of an organic compound required 10 mL of 1 M H 2SO 4 for complete neutralization of the evolved ammonia. The percentage of nitrogen in the compound is: 56.0 % 28.0 % 14.0 % 42.0 % During the Carius method for the estimation of iodine, 0.2 g of an organic compound yielded 0.188 g of AgI . What is the percentage of iodine in the compound? (Atomic weights: Ag = 108, I = 127 ) 50.8 % 42.4 % 63.5 % 31.7 % In a modified Kjeldahl's method, the ammonia evolved is sometimes absorbed in a solution of which acid, which can then be titrated directly against a standard acid without the use of a back-titration? Boric acid Hydrochloric acid Sulfuric acid Nitric acid If an organic compound contains both Nitrogen and Sulfur, and it is fused with an EXCESS of sodium, what products are formed in the Lassaigne's extract? NaCN and Na 2S Only NaSCN Only Na 2S No reaction occurs Which of the following compounds will NOT give a positive Lassaigne's test for nitrogen despite containing nitrogen? NH 2NH 2 (Hydrazine) C 6H 5NH 2 (Aniline) CH 3CN (Acetonitrile) H 2NCONH 2 (Urea) In the estimation of phosphorus, an organic compound is heated with HNO 3 and then with ammonium molybdate. A yellow precipitate is formed. What is the next step to quantify phosphorus as Mg 2P 2O 7 ? Add magnesia mixture to the solution obtained after boiling the yellow precipitate with NH 4OH . Ignite the yellow precipitate directly. Dry the yellow precipitate at 110 C and weigh it. Add BaCl 2 to the solution. For which of the following compounds is the Kjeldahl method suitable for nitrogen estimation? C 6H 5NH 2 (Aniline) C 6H 5NO 2 (Nitrobenzene) Pyridine Azobenzene ( C 6H 5N=NC 6H 5 ) In the detection of sulfur using Lassaigne's test, the sodium nitroprusside reagent reacts with the extract to give a violet color. The oxidation state of Iron ( Fe ) in the resulting complex [Fe(CN) 5NOS] 4- is: +2 +3 0 +1 An organic compound contains C, H, and S . In the Carius method, 0.125 g of this compound gave 0.233 g of BaSO 4 . What is the percentage of sulfur in the compound? (Atomic mass: Ba = 137, S = 32, O = 16 ) 25.6 % 12.8 % 32.0 % 51.2 % In the Dumas method, 0.2 g of an organic compound yielded 31.36 mL of nitrogen gas at STP. The percentage of nitrogen in the compound is: 19.6 % 28.0 % 14.0 % 7.0 % In the qualitative detection of carbon and hydrogen, the organic compound is heated with dry copper(II) oxide ( CuO ). Carbon is oxidized to CO 2 and is detected by passing through: Lime water, which turns milky Anhydrous copper sulfate, which turns blue Potassium dichromate, which turns green Silver nitrate, which forms a white precipitate In the Lassaigne's test, why is the sodium extract boiled with concentrated HNO 3 before testing for halogens? To decompose NaCN and Na 2S that might interfere with the AgNO 3 test To oxidize the halogens to their respective oxyacids To increase the solubility of silver halides To convert silver nitrate into silver oxide Which of the following statements about Kjeldahl's method is CORRECT? It cannot be used for compounds containing nitrogen in the ring (e.g., pyridine) It is used for the direct estimation of oxygen It involves the collection of nitrogen gas in a nitrometer It uses copper gauze to reduce nitrogen oxides In the quantitative estimation of phosphorus, 0.20 g of an organic compound gave 0.222 g of Mg 2P 2O 7 . What is the percentage of phosphorus in the compound? (Atomic mass: Mg = 24, P = 31, O = 16 ) 31 % 62 % 15.5 % 20 % In the Carius method for the estimation of phosphorus, the mass of magnesium pyrophosphate ( Mg 2P 2O 7 ) obtained is 0.222 g from 0.5 g of an organic compound. The percentage of phosphorus is: (Atomic mass: P=31, Mg=24, O=16 ) 12.4% 25.2% 6.2% 31.0% In the estimation of Nitrogen by Kjeldahl's method, 1 g of an organic compound was digested and the evolved ammonia was absorbed in 50 mL of 0.5 M H 2SO 4 . The unreacted acid required 60 mL of 0.5 M NaOH for neutralization. What is the percentage of nitrogen in the compound? 28% 14% 42% 7% In the estimation of Sulfur, 0.16 g of an organic compound gave 0.466 g of BaSO 4 . What is the percentage of sulfur in the compound? (Atomic mass: Ba=137, S=32, O=16 ) 40% 20% 32% 16% Which of the following drying agents is preferred in the Liebig method for the absorption of water when the organic compound contains nitrogen? Anhydrous magnesium perchlorate Anhydrous calcium chloride Concentrated sulfuric acid Phosphorus pentoxide In the estimation of phosphorus, the organic compound is heated with fuming HNO 3 and ammonium molybdate. The yellow precipitate formed is ammonium phosphomolybdate. What is its chemical formula? (NH 4) 3PO 4 12MoO 3 (NH 4) 3PO 4 9MoO 3 (NH 4) 2HPO 4 12MoO 3 (NH 4) 3PO 4 6MoO 3 In the estimation of nitrogen by Kjeldahl's method, the ammonia evolved from 0.5 g of an organic compound neutralized 10 mL of 1 M H 2SO 4 . The percentage of nitrogen in the compound is: 56% 28% 14% 42% In the Carius method for the estimation of iodine, 0.32 g of an organic compound gave 0.47 g of AgI . The percentage of iodine in the compound is: (Atomic mass: Ag=108, I=127 ) 79.37% 39.68% 50.00% 25.40% During the qualitative analysis of carbon and hydrogen, the presence of hydrogen is confirmed by the formation of blue color when the products are passed over: Anhydrous copper sulfate Anhydrous calcium chloride Potassium hydroxide solution Calcium hydroxide solution In the Dumas method, 0.15 g of an organic compound gave 30 mL of nitrogen gas collected at 300 K and 760 mm Hg pressure. What is the mass of nitrogen at STP? (Assume 1 atm = 760 mm Hg) 0.034 g 0.025 g 0.042 g 0.015 g In the Carius method of estimation of phosphorus, 0.25 g of an organic compound gave 1.88 g of ammonium phosphomolybdate (NH 4) 3PO 4 12MoO 3 . The percentage of phosphorus in the compound is: (Atomic mass of P = 31 , Molar mass of precipitate = 1877 ) 12.4 % 10.2 % 15.5 % 8.4 % The amino acid that gives a red-blood colour on treating its sodium fusion extract with sodium nitroprusside is leucine threonine methionine serine In the Kjeldahl method, the nitrogen present in the organic compound is converted into which of the following during the digestion with concentrated H 2SO 4 ? (NH 4) 2SO 4 (NH 4) 3PO 4 (NH 4) 2CO 3 (NH 4)Cl A compound contains 50 % sulfur and 50 % oxygen by mass. Its empirical formula is: (Atomic mass: S = 32, O = 16 ) SO 2 SO SO 3 S 2O During the test for halogens in Lassaigne's extract, the appearance of a white precipitate soluble in NH 4OH indicates the presence of: Chlorine Bromine Iodine Fluorine The percentage of oxygen in an organic compound is usually determined by: The difference between 100 and the sum of percentages of all other elements. Direct estimation using the Dumas method. Direct estimation using the Carius method. Direct estimation using the Kjeldahl method. Which of the following elements is detected using the Beilstein test? Halogens Nitrogen Sulfur Phosphorus In the Carius tube, the organic compound is heated with fuming nitric acid in the presence of silver nitrate to estimate: Halogens Nitrogen Carbon Hydrogen In the estimation of carbon and hydrogen (Liebig's method), the CO 2 and H 2O are absorbed respectively in: KOH solution and anhydrous CaCl 2 Anhydrous CaCl 2 and KOH solution H 2SO 4 and NaOH Ca(OH) 2 and P 2O 5 In the qualitative analysis of an organic compound, the Beilstein test is performed by heating the compound on a copper wire. The appearance of a green or bluish-green flame indicates the presence of: Halogens Nitrogen Sulfur Phosphorus In the estimation of sulfur by Carius method, the mass of BaSO 4 is converted to the mass of sulfur. What is the numerical value of the factor ( Atomic Mass of S / Molecular Mass of BaSO 4) ? 32/233 32/137 64/233 16/233 During the Lassaigne's test for sulfur, the addition of acetic acid and lead acetate to the sodium extract results in a black precipitate. The formula of this precipitate is: PbS Na 2S Pb(SO 4) 2 FeS In the estimation of oxygen by the indirect method, an organic compound containing C, H , and O is analyzed. If the percentage of Carbon is 40.0 % and Hydrogen is 6.67 % , what is the percentage of Oxygen? 53.33% 46.67% 33.33% 60.00% In the Carius method for the estimation of halogens, the organic compound is heated with which of the following in a sealed tube? Fuming HNO 3 and AgNO 3 Concentrated H 2SO 4 Sodium metal Potassium dichromate In the Dumas method for the estimation of nitrogen, the percentage of nitrogen is calculated using the formula %N = 28 22400 V STP m 100 . What does ' V STP ' represent? Volume of nitrogen gas at 273 K and 760 mm Hg pressure. Volume of nitrogen gas at 298 K and 1 atm pressure. Total volume of the nitrometer. Volume of the organic compound used. In Kjeldahl's method, which of the following substances can be used as a catalyst to accelerate the digestion process along with concentrated H 2SO 4 ? Selenium Nickel Iron powder Sodium chloride In the Lassaigne's test for nitrogen, why is it necessary to use a freshly prepared solution of Ferrous Sulfate ( FeSO 4 )? To prevent the oxidation of Fe 2+ to Fe 3+ by atmospheric oxygen To ensure the solution is acidic enough To prevent the formation of sodium cyanide To speed up the reaction with NaOH An organic compound contains 92.3 % Carbon and 7.7 % Hydrogen. Its empirical formula is: CH CH 2 C 2H 2 CH 4 In the Dumas method, the nitrogen gas is collected at 300 K. The atmospheric pressure is 715 mm Hg and the aqueous tension at 300 K is 15 mm Hg. What is the pressure of the dry nitrogen used for calculation? 700 mm Hg 730 mm Hg 715 mm Hg 685 mm Hg In the Carius method for the estimation of sulfur, the percentage of sulfur is calculated using the formula: %S = 32 233 mass of BaSO 4 mass of compound 100 %S = 32 137 mass of BaSO 4 mass of compound 100 %S = 80 188 mass of AgBr mass of compound 100 %S = 16 233 mass of BaSO 4 mass of compound 100 During the qualitative test for hydrogen, the anhydrous copper(II) sulfate turns blue. This is due to the formation of: CuSO 4 5H 2O Cu(OH) 2 CuH 2 [Cu(NH 3) 4]SO 4 A hydrocarbon contains 85.7 % Carbon and 14.3 % Hydrogen. What is its empirical formula? CH 2 CH CH 3 C 2H 5 During the Dumas method for nitrogen estimation, the nitrogen gas is collected in a graduated tube called a/an: Nitrometer Eudiometer Volumeter Azotometer Kjeldahl's method for the estimation of nitrogen is NOT applicable to which of the following compounds? Nitrobenzene Aniline Benzamide Ethylamine Which of the following organic compounds will give a blood red color in Lassaigne's test for the simultaneous detection of nitrogen and sulfur? Thiocyanates of Sodium Thiourea Sulfanilic acid Benzothiazole Which reagent is used in the Carius method for the estimation of phosphorus? Magnesia mixture Ammonium molybdate Silver nitrate Barium chloride Sodium nitroprusside reacts with the sulfide ion in the Lassaigne's extract to give a violet color. This is due to the formation of: [Fe(CN) 5NOS] 4- [Fe(CN) 6] 4- [Fe(CN) 5S] 3- Na 2S During the Lassaigne's test, why is the sodium extract boiled with concentrated HNO 3 before testing for halogens? To decompose NaCN and Na 2S if present To oxidize the halide ions To help the precipitation of AgCl To neutralize the excess sodium hydroxide In the quantitative estimation of nitrogen by the Dumas method, why is the nitrometer tube filled with KOH solution instead of water? To absorb CO 2 and other acidic gases, leaving only N 2 To prevent the dissolution of nitrogen gas To act as a catalyst for the reduction of nitrogen oxides To maintain a constant temperature for the gas In the Dumas method, the copper gauze used at the exit end of the combustion tube serves to: Reduce oxides of nitrogen to nitrogen gas Oxidize carbon to CO 2 Oxidize hydrogen to H 2O Absorb any moisture produced In the Liebig's method for the estimation of Carbon and Hydrogen, the CO 2 produced is absorbed in: Potassium hydroxide solution Anhydrous calcium chloride Concentrated sulfuric acid Magnesium perchlorate In Kjeldahl's method, the percentage of nitrogen is calculated using the formula: 1.4 N V W 14 N V W 28 V 22400 W 7 N V W Phosphorus is detected by heating the organic compound with an oxidizing agent like Na 2O 2 . The phosphate formed is then tested with: Ammonium molybdate Barium chloride Silver nitrate Potassium ferrocyanide In the qualitative analysis of phosphorus, the organic compound is heated with sodium peroxide. The resulting solution is treated with nitric acid and ammonium molybdate to give a yellow precipitate. The formula of this precipitate is: (NH 4) 3PO 4.12MoO 3 (NH 4) 2HPO 4.12MoO 3 Mg(NH 4)PO 4 Na 3PO 4.12MoO 3 During the digestion stage of Kjeldahl's method, potassium sulfate ( K 2SO 4 ) is added to the concentrated sulfuric acid. What is its primary function? To raise the boiling point of sulfuric acid To act as a reducing agent To act as a catalyst for the reaction To prevent the formation of nitrogen oxides During the Lassaigne's test for halogens, why is it that fluorine is generally not detected using the silver nitrate test? Silver fluoride ( AgF ) is soluble in water Silver fluoride ( AgF ) is a gas Fluorine does not react with sodium metal Silver fluoride ( AgF ) is a highly explosive solid An organic compound contains 40 % Carbon, 6.67 % Hydrogen, and the rest is Oxygen. What is its empirical formula? CH 2O CHO C 2H 4O CH 4O In the Dumas method, the mixture of gases (including nitrogen and oxides of nitrogen) is passed over a heated copper gauze. The role of this copper gauze is to: Reduce oxides of nitrogen back to nitrogen gas Oxidize carbon monoxide to carbon dioxide Absorb moisture from the gas stream Act as a catalyst for nitrogen gas combustion In Kjeldahl's method, copper sulfate ( CuSO 4 ) is often added along with sulfuric acid. Its role is: To act as a catalyst To increase the boiling point To prevent bumping To oxidize the carbon to CO 2 In the estimation of sulfur by the Carius method, the fuming nitric acid acts as: An oxidizing agent A reducing agent A dehydrating agent A solvent only In the Carius method for the estimation of sulfur, the mass of barium sulfate ( BaSO 4 ) is used to calculate the percentage of sulfur. The conversion factor used is: 32 / 233 32 / 137 16 / 233 80 / 233 Which of the following organic compounds will NOT give a positive test for nitrogen using Kjeldahl's method? Azobenzene Acetamide Urea Ethylamine In the Carius method for the estimation of phosphorus, the phosphorus present in the organic compound is first oxidized to phosphoric acid and then precipitated as: MgNH 4PO 4 Mg 2P 2O 7 Na 3PO 4 P 2O 5 In the Liebig's method for estimation of carbon and hydrogen, what is the role of the oxidized copper gauze? To ensure complete oxidation of the compound To absorb nitrogen oxides To absorb moisture To act as a reducing agent If an organic compound contains both Nitrogen and Sulfur, Lassaigne's fusion with insufficient sodium yields: NaSCN NaCN and Na 2S Na 2SO 4 NaNH 2 Which of the following tests is used to identify the presence of a halogen in an organic compound without the use of Lassaigne's extract, although it is not always reliable? Beilstein test Liebig's test Dumas test Carius test In the Aluise method (direct estimation of oxygen), the organic compound is decomposed and the oxygen is converted to CO by passing over: Red hot coke Platinized asbestos Copper oxide Magnesium oxide In the detection of nitrogen, the sodium fusion extract is boiled with FeSO 4 and then acidified with concentrated HCl . The appearance of a Prussian blue color indicates nitrogen. What is the role of HCl ? To dissolve the ferric hydroxide and provide Fe 3+ ions To oxidize Fe 2+ to Fe 3+ To reduce the cyanide ions To prevent the formation of sodium chloride In the Schütze method for the estimation of oxygen, the iodine produced is titrated against: Sodium thiosulfate Potassium permanganate Sodium hydroxide Hydrochloric acid In the Carius method for the estimation of halogens, 250 mg of an organic compound gave 141 mg of AgBr . The percentage of bromine in the compound is: (Atomic mass Ag = 108, Br = 80 ) 24% 36% 48% 60% Which of the following organic compounds will give a positive test with sodium nitroprusside but a negative test for nitrogen in the Lassaigne's extract? A compound containing Sulfur but no Nitrogen A compound containing Nitrogen but no Sulfur A compound containing both Nitrogen and Sulfur A compound containing Halogens only Why is sodium metal specifically chosen for the Lassaigne's fusion test? It has a low melting point and is highly reactive It is the only metal that can react with Nitrogen It forms compounds that are all insoluble in water It acts as an oxidizing agent for the organic compound In the Dumas method for the estimation of nitrogen, why is the nitrogen gas collected over a solution of Potassium Hydroxide ( KOH )? To absorb carbon dioxide and other acidic gases produced during combustion To catalyze the conversion of nitrogen oxides to nitrogen gas To prevent the nitrogen from reacting with oxygen To dry the nitrogen gas by absorbing water vapor In the Lassaigne's test for the simultaneous detection of Nitrogen and Sulfur, a blood-red coloration is obtained upon adding FeCl 3 . The formula of the complex responsible for this is: [Fe(SCN)] 2+ Fe 4[Fe(CN) 6] 3 Na 2[Fe(CN) 5NOS] Fe(OH) 3 An organic compound contains 80 % Carbon and 20 % Hydrogen by mass. Its empirical formula is: CH 3 CH 2 CH 4 C 2H 5 In the Carius method for halogens, silver bromide ( AgBr ) is distinguished from silver chloride ( AgCl ) by its color and solubility in ammonium hydroxide. AgBr is: Pale yellow and sparingly soluble in NH 4OH White and readily soluble in NH 4OH Yellow and insoluble in NH 4OH Curdy white and insoluble in NH 4OH In the quantitative estimation of phosphorus, the mass of Mg 2P 2O 7 is used to calculate the percentage of phosphorus. The percentage of P is given by: 62 222 mass of Mg 2P 2O 7 mass of compound 100 31 222 mass of Mg 2P 2O 7 mass of compound 100 62 111 mass of Mg 2P 2O 7 mass of compound 100 31 111 mass of Mg 2P 2O 7 mass of compound 100 Prussian blue, formed during the detection of nitrogen in Lassaigne's test, contains iron in which oxidation states? Fe 3+ outside the coordination sphere and Fe 2+ inside the sphere Fe 2+ outside the coordination sphere and Fe 3+ inside the sphere Both iron atoms are in the +3 oxidation state Both iron atoms are in the +2 oxidation state In the Dumas method, 0.20 g of an organic compound yielded 22.4 mL of nitrogen gas at STP. The percentage of nitrogen in the compound is: 14% 28% 7% 21% The Beilstein test is used to detect halogens, but it is not a definitive test because: Some nitrogen-containing compounds like urea and thiourea also give a positive green flame It cannot detect fluorine It requires a very large amount of the organic compound The copper wire used always produces a green flame regardless of the compound Kjeldahl's method is successfully used for the estimation of nitrogen in which of the following compounds? Acetamide Nitrobenzene Azobenzene Pyridine The silver halide which is soluble in ammonium hydroxide is: AgCl AgBr AgI None of these In Lassaigne's test for the detection of nitrogen, sulfur, and halogens, why is the organic compound fused with metallic sodium? To convert covalent bonds into ionic bonds. To reduce the organic compound to carbon and hydrogen. To oxidize the elements present in the compound. To form gaseous products for easier identification. In the estimation of Nitrogen by the Dumas method, 0.30 g of an organic compound gave 50 mL of nitrogen at STP. The percentage of nitrogen in the compound is: 20.83 % 15.20 % 10.45 % 25.12 % In the estimation of sulfur using the Carius method, 0.157 g of an organic compound gave 0.4813 g of barium sulfate ( BaSO 4 ). What is the percentage of sulfur in the compound? (Atomic mass: Ba = 137, S = 32, O = 16 ) 42.10 % 32.50 % 21.05 % 10.50 % In the Carius method for the estimation of halogens, 0.25 g of an organic compound yielded 0.188 g of AgBr . The percentage of bromine in the compound is: (Atomic mass: Ag = 108, Br = 80 ) 32 % 24 % 40 % 16 % In the estimation of sulfur, the organic compound is heated with Na 2O 2 or fuming HNO 3 . This step is necessary to: Convert sulfur into sulfate ions. Convert sulfur into sulfide ions. Convert sulfur into sulfur dioxide gas. Reduce the sulfur to its elemental form. In the Dumas method for the estimation of nitrogen, a heated copper gauze is placed at the exit end of the combustion tube. What is the specific function of this copper gauze? To reduce any oxides of nitrogen formed to free nitrogen gas To oxidize nitrogen gas to nitrogen dioxide To absorb any excess carbon dioxide produced To react with unreacted oxygen gas A mixture of 0.50 g of an organic compound was analyzed using the Liebig method. If 0.44 g of CO 2 was produced, what is the percentage of carbon in the compound? 24 % 12 % 44 % 60 % In the Carius method for the estimation of halogens, 0.20 g of an organic compound gave 0.188 g of AgBr . The percentage of bromine in the compound is: (Atomic mass: Ag = 108, Br = 80 ) 40 % 20 % 80 % 10 % During the Lassaigne's test for nitrogen, the sodium fusion extract is acidified with concentrated H 2SO 4 or HCl and treated with FeSO 4 and FeCl 3 . If nitrogen is present, Prussian blue color is formed. Which of the following is the intermediate complex formed before the addition of ferric ions? Na 4[Fe(CN) 6] Na 3[Fe(CN) 6] Fe(OH) 2 Fe 4[Fe(CN) 6] 3 In the estimation of phosphorus using the Carius method, the phosphorus present in the organic compound is oxidized to phosphoric acid and finally precipitated as: MgNH 4PO 4 Mg 2P 2O 7 Ca 3(PO 4) 2 Na 3PO 4 In the sodium fusion test for organic compounds, the nitrogen of an organic compound is converted into: NaCN NaNH 2 NaNO 2 NaNO 3 A compound was found to contain 80 % carbon and 20 % hydrogen by weight. If the vapor density of the compound is 15 , its molecular formula is: C 2H 6 CH 4 C 2H 4 C 3H 8 In the quantitative estimation of hydrogen by the Liebig method, 0.18 g of water was collected from 0.20 g of an organic compound. The percentage of hydrogen in the compound is: 10 % 20 % 5 % 1 % In the Dumas method, the volume of nitrogen collected in the nitrometer is corrected to STP. Which of the following is the correct pressure correction if the atmospheric pressure is P , the aqueous tension is f , and the volume is V ? (P - f) V (P + f) V (P / f) V P (V - f) A mixture of camphor and benzoic acid can be separated by chemical extraction. If we use an aqueous solution of a reagent to selectively dissolve benzoic acid, which reagent is most appropriate? NaHCO 3 solution Dilute HCl Cold water Diethyl ether In the Lassaigne's test, if both nitrogen and sulfur are present, the formation of which ion leads to a blood-red coloration with Fe 3+ ions? SCN - CN - S 2- NO 2 - In the Carius method for the estimation of halogens, fuming HNO 3 is used because: It oxidizes the organic matter and converts halogens to halide ions. It acts as a solvent for the silver halide precipitate. It prevents the precipitation of silver nitrate. It reduces silver ions to metallic silver. A compound contains 24.27 % Carbon, 4.07 % Hydrogen, and 71.65 % Chlorine. What is its empirical formula? CH 2Cl CHCl 2 C 2H 4Cl CH 3Cl Which of the following organic compounds will NOT give a blue-green flame in the Beilstein test? Urea Chlorobenzene Chloroform Bromobenzene In the quantitative analysis of Carbon and Hydrogen (Liebig's method), why is a small portion of the combustion tube filled with copper(II) oxide ( CuO )? To ensure complete oxidation of any remaining traces of carbon and hydrogen. To absorb the CO 2 produced during the reaction. To catalyze the decomposition of the organic compound. To reduce nitrogen oxides back to nitrogen gas. In the detection of halogens, if a Lassaigne's extract is treated with AgNO 3 and a yellow precipitate is formed which is COMPLETELY INSOLUBLE in NH 4OH , which halogen is present? Iodine Bromine Chlorine Fluorine During the estimation of nitrogen by the Dumas method, the gas collected in the Nitrometer is: N 2 NH 3 NO 2 N 2O An organic compound on analysis was found to contain 10.06 % Carbon, 0.84 % Hydrogen, and 89.10 % Chlorine. What is its empirical formula? (Atomic mass: C=12, H=1, Cl=35.5 ) CHCl 3 CH 2Cl 2 CCl 4 C 2HCl 3 Why is the Kjeldahl method not suitable for compounds containing a nitro group ( -NO 2 )? The nitrogen in the nitro group is not converted to ammonium sulfate under the reaction conditions. The nitro group makes the compound highly explosive upon heating. The nitro group reacts with NaOH to form poisonous gases. The nitrogen in the nitro group is lost as N 2 gas during digestion. The 'Lassaigne's test' for the detection of nitrogen fails for which of the following compounds? NH 2NH 2 C 6H 5NH 2 CH 3CN NH 2CONH 2 In the Carius method for the estimation of chlorine, 0.378 g of an organic compound gave 0.574 g of silver chloride ( AgCl ). What is the percentage of chlorine in the compound? (Atomic mass: Ag = 108, Cl = 35.5 ) 37.56% 42.10% 25.33% 50.00% During the quantitative estimation of Carbon, 0.20 g of an organic compound on complete combustion yielded 0.66 g of CO 2 . The percentage of Carbon in the compound is: 90% 40% 60% 80% Which of the following nitrogen-containing compounds will NOT give a positive Lassaigne's test for nitrogen because it does not contain carbon? Hydrazine ( NH 2NH 2 ) Urea ( NH 2CONH 2 ) Aniline ( C 6H 5NH 2 ) Glycine ( NH 2CH 2COOH ) In the Liebig method, if the organic compound contains sulfur or halogens, which modification is made to the combustion tube to prevent interference with Carbon and Hydrogen estimation? A silver spiral is placed in the tube The CuO is replaced with PbCrO 4 The tube is washed with HNO 3 Anhydrous CaCl 2 is replaced with Mg(ClO 4) 2 In the Carius method for the estimation of phosphorus, the reagent used to precipitate the phosphate ions after oxidation is: Magnesia mixture ( MgCl 2 + NH 4Cl + NH 4OH ) Ammonium molybdate in HNO 3 Silver nitrate in HNO 3 Barium chloride solution What is the empirical formula of a compound that contains 26.6 % Carbon, 2.2 % Hydrogen, and 71.2 % Oxygen? CHO 2 CH 2O C 2H 2O 4 C 2HO 2 In the qualitative detection of phosphorus, why is the organic compound fused with sodium peroxide ( Na 2O 2 )? To oxidize phosphorus to phosphate To convert phosphorus into sodium phosphide To reduce phosphorus to phosphine gas To remove carbon and hydrogen as CO 2 and H 2O