Free NEET Chemistry multiple-choice questions on Titrimetric Analysis. Attempt each question and reveal the answer with a full explanation.
The chemical formula of Mohr's salt, used as a primary standard in titrimetry, is: FeSO 4 (NH 4) 2SO 4 6H 2O Fe 2(SO 4) 3 (NH 4) 2SO 4 24H 2O FeSO 4 7H 2O K 2SO 4 Al 2(SO 4) 3 24H 2O A secondary standard solution is one whose concentration: Must be determined by titration against a primary standard Is calculated directly from the weight of the solute Does not change with time or atmospheric exposure Is always 1.0 M The addition of boiling chips or pumice stones to a liquid before distillation is done to: Prevent 'bumping' by providing nucleation sites for bubble formation Increase the boiling point of the liquid Decrease the rate of evaporation Catalyze the separation of components For a liquid that decomposes at its normal boiling point, which of the following purification techniques is the most appropriate? Distillation under reduced pressure Steam distillation Simple distillation Fractional distillation A mixture of two liquids A (boiling point 350 K ) and B (boiling point 353 K ) can be effectively separated by: Fractional distillation Simple distillation Steam distillation Crystallization In the titration of KMnO 4 against oxalic acid, which of the following acts as a self-indicator? KMnO 4 Oxalic acid Mn 2+ ions Starch During a titration, the point at which the indicator changes color is known as the: End point Equivalence point Neutralization point Standard point Which of the following is NOT a primary standard in titrimetric analysis? NaOH Na 2CO 3 Oxalic acid K 2Cr 2O 7 Which of the following describes the 'Self-indicator' property of KMnO 4 ? It is intensely colored, and its disappearance/appearance marks the end point. It changes color from red to blue at the end point. It reacts with starch to give a blue color. It is colorless but becomes pink when oxidized. The pH range for the color change of Methyl Orange indicator is: 3.1 – 4.4 8.3 – 10.0 1.2 – 2.8 6.0 – 7.6 During the preparation of Mohr’s salt solution (Ferrous ammonium sulphate), which of the following acid is added to prevent hydrolysis of Fe 2+ ion? dilute hydrochloric acid concentrated sulphuric acid dilute nitric acid dilute sulphuric acid During the titration of a weak acid like oxalic acid with a strong base like NaOH , which indicator is most suitable? Phenolphthalein Methyl orange Methyl red Starch Phenolphthalein is used as an indicator for the titration of sodium hydroxide solution against a standard solution of oxalic acid. The colour change that is observed at an alkaline pH close to the equivalence point during this titration is: Pink to colourless Pinkish red to yellow Colourless to pink Yellow to pinkish red During the titration of KMnO 4 against oxalic acid in acidic medium, why is the solution heated to about 60-70 C ? To increase the rate of reaction To prevent the decomposition of KMnO 4 To decrease the solubility of CO 2 To act as a catalyst Which of the following indicators is most suitable for a titration between a weak acid ( CH 3COOH ) and a strong base ( NaOH )? Phenolphthalein Methyl orange Methyl red Bromocresol green During the titration of Na 2S 2O 3 with I 2 , starch is added as an indicator. The end-point is marked by the: Disappearance of the blue color Appearance of a blue color Appearance of a pink color Disappearance of a yellow color In the titration of KMnO 4 against oxalic acid, the reaction is slow initially but becomes fast as the titration proceeds. This is due to the autocatalysis by: Mn 2+ MnO 2 C 2O 4 2- Mn 3+ KMnO 4 is not used as a primary standard in titrimetric analysis because: It is difficult to obtain in a high state of purity and its concentration changes over time It is a very weak oxidizing agent It reacts with CO 2 from the atmosphere It is highly volatile The equivalent weight of potassium dichromate ( K 2Cr 2O 7 ) in an acidic medium is given by (where M is the molar mass): M/6 M/3 M/1 M/2 Which of the following indicators is most suitable for the titration of a strong acid like HCl against a weak base like NH 4OH ? Methyl orange Phenolphthalein Thymol blue Bromothymol blue In the titration of Na 2S 2O 3 against I 2 (Iodimetry), the starch indicator is added: Near the end point when the solution becomes light straw yellow At the very beginning of the titration After the end point is reached When the solution is still deep dark brown In the estimation of Nitrogen by the Kjeldahl method, the percentage of nitrogen is calculated as: %N = 1.4 N V W %N = 2.8 N V W %N = 14 N V W %N = 0.14 N V W Which of the following is used as a primary standard in the standardization of KMnO 4 ? Oxalic acid NaOH HCl H 2SO 4 The titration of KMnO 4 against FeSO 4 is typically carried out in the presence of dilute H 2SO 4 instead of HCl . This is because: HCl is oxidized to Cl 2 by KMnO 4 Oxidation of Fe 2+ is incomplete in HCl The reaction between KMnO 4 and HCl is too slow The end point is masked by the color of HCl In the estimation of nitrogen by the Dumas method, 0.30 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 actual pressure of the nitrogen gas is: 700 mm 715 mm 730 mm 685 mm What is the equivalent weight of Sodium Thiosulfate ( Na 2S 2O 3 5H 2O ) in its reaction with Iodine? (Molar mass = M ) M M/2 M/5 2M In the titration of 20 mL of 0.1 ,M KMnO 4 against FeSO 4 in an acidic medium, the number of moles of Fe 2+ oxidized is: 0.010 ,mol 0.002 ,mol 0.005 ,mol 0.020 ,mol The internal indicator used in the titration of K 2Cr 2O 7 against ferrous ammonium sulfate is: Diphenylamine Phenolphthalein Methyl orange Starch In the estimation of Fe 2+ by KMnO 4 , the use of HCl is avoided because: It reacts with KMnO 4 to evolve Cl 2 . It acts as an oxidizing agent. It precipitates Fe 2+ as FeCl 2 . It reduces Fe 3+ back to Fe 2+ . In the Victor Meyer's method for determining the molecular mass of a volatile liquid, the displaced air is collected over water. Which correction must be applied to the observed pressure? Subtract the aqueous tension Add the aqueous tension Multiply by the aqueous tension Divide by the aqueous tension During the titration of oxalic acid with KMnO 4 , if the temperature is too low, the end point is difficult to detect because of the formation of: MnO 2 (brown precipitate) Mn 2O 7 (green oil) Mn(OH) 2 K 2MnO 4 (green solution) In a titration between a strong acid and a strong base, the pH curve shows a vertical region. Which of the following graphs correctly represents this? pH vs volume of base added pH vs volume of acid added pOH vs pH Conductivity vs volume A mixture of Na 2CO 3 and NaHCO 3 is titrated against HCl . If phenolphthalein is used as the indicator, the end point corresponds to: Half the Na 2CO 3 converted to NaHCO 3 Full neutralization of Na 2CO 3 and NaHCO 3 Full neutralization of Na 2CO 3 only Half neutralization of NaHCO 3 The equivalent weight of KMnO 4 in acidic medium is (where M is the molar mass): M/5 M/3 M/1 M/2 In neutral or faintly alkaline medium, the equivalent weight of KMnO 4 (Molar mass = M) is: M/3 M/5 M/1 M/2 Steam distillation is based on the principle that the total vapor pressure ( P ) of the system is equal to: P = p water + p organic , liquid P = p water - p organic , liquid P = p water p organic , liquid P = p water / p organic , liquid In the Dumas method for estimation of nitrogen, 0.3 g of an organic compound gave 50 mL of nitrogen collected at 300 K and 715 mm pressure. The aqueous tension at 300 K is 15 mm. The volume of N 2 at STP is: 41.9 mL 50.0 mL 45.2 mL 38.5 mL During the titration of a strong acid (e.g., HCl ) with a weak base (e.g., NH 4OH ), the pH at the equivalence point will be: Less than 7 Exactly 7 Greater than 7 Neutral In the estimation of Fe 2+ using K 2Cr 2O 7 in acidic medium, why is H 3PO 4 added? To lower the reduction potential of the Fe 3+ /Fe 2+ system by complexation To act as a catalyst for the reaction To maintain the pH of the solution To act as an internal indicator During the titration of K 2Cr 2O 7 against Fe 2+ , the internal indicator used is N -phenylanthranilic acid. The color change at the end point is: Green to violet-red Pink to colorless Colorless to blue Yellow to green The number of moles of KMnO 4 required to completely oxidize 1 mole of ferrous oxalate ( FeC 2O 4 ) in an acidic medium is: 0.6 1.0 1.5 0.4 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 % In the titration of Fe 2+ with KMnO 4 in the presence of HCl , Zimmermann-Reinhardt (Z-R) reagent is added to: Prevent the oxidation of chloride ions by KMnO 4 Act as an external indicator Maintain the pH of the solution at 7 Increase the rate of reaction In a double titration of a mixture of Na 2CO 3 and NaHCO 3 against HCl , if V 1 is the volume of HCl used with phenolphthalein and V 2 is the total volume of HCl used with methyl orange, the volume of HCl required for NaHCO 3 only is: V 2 - 2V 1 V 2 - V 1 2V 1 - V 2 V 1 / 2 Which of the following is a primary standard used in redox titrations involving Fe 2+ estimation? K 2Cr 2O 7 KMnO 4 FeSO 4 NaOH In an acidic medium, 10 mL of 0.25 M oxalic acid is titrated with KMnO4 solution. If the volume of KMnO4 solution required to reach end point is 10 mL, the strength of the KMnO4 solution is 0.10 M 0.20 M 0.25 M 0.15 M Which of the following internal indicators is commonly used in the titration of Fe 2+ ions against K 2Cr 2O 7 in acidic medium? Diphenylamine Phenolphthalein Methyl Orange Eriochrome Black T Distillation under reduced pressure (vacuum distillation) is used for liquids which: Decompose at or below their normal boiling points Have very low boiling points Are miscible with water Are non-volatile The pH range for the color change of the indicator Phenolphthalein is approximately: 8.2 - 10.0 3.1 - 4.4 6.0 - 7.6 1.2 - 2.8 In the standardization of sodium thiosulfate ( Na 2S 2O 3 ) using iodine, what is the equivalent weight of iodine? (Molar mass of I 2 = M ) M/2 M M/1 2M