Identify the incorrect statements regarding primary standard of titrimetric analysis (A) It should be purely available in dry form. (B) It should not undergo chemical change in air. (C) It should be hygroscopic and should react with another chemical instantaneously and stoichiometrically. (D) It should be readily soluble in water. (E) KMnO4 & NaOH can be used as primary standard. Choose the correct answer from the options given below :
1
(C) and (D) only
2
(B) and (E) only
3
(A) and (B) only
4
(C) and (E) only
Official Solution
Correct Option: (4)
To determine the incorrect statements regarding the primary standard of titrimetric analysis, let's evaluate each option:
(A) It should be purely available in dry form: This is a correct statement. Primary standards should be of a high purity and stable form, typically in a dry state, to ensure accurate measurement.
(B) It should not undergo chemical change in air: This is also a correct statement. Primary standards must be stable in air so they don't react with moisture or gases, ensuring that their mass remains constant over time.
(C) It should be hygroscopic and should react with another chemical instantaneously and stoichiometrically: This statement is incorrect. A primary standard should not be hygroscopic (meaning it should not absorb moisture from the air) as this would affect its mass and thus the accuracy of the titration.
(D) It should be readily soluble in water: This is a correct statement. Solubility ensures that the compound can dissolve fully to provide a consistent and accurate reaction.
(E) KMnO4 & NaOH can be used as primary standards: This statement is incorrect. KMnO4 is not used as a primary standard due to its propensity to decompose and its instability in air. Similarly, NaOH is hygroscopic and absorbs water and carbon dioxide from the air, making it unsuitable as a primary standard.
Based on this analysis, the incorrect statements are (C) and (E).
02
PYQ 2025
medium
chemistryID: jee-main
In Dumas' method for estimation of nitrogen 0.4 g of an organic compound gave 60 mL of nitrogen collected at 300 K temperature and 715 mm Hg pressure. The percentage composition of nitrogen in the compound is
(Given : Aqueous tension at 300 K = 15 mm Hg)
1
15.71%
2
20.95%
3
17.46%
4
7.85%
Official Solution
Correct Option: (1)
Given: Mass of organic compound = 0.4 g Volume of nitrogen collected = 60 mL = L Temperature (T) = 300 K Pressure of wet nitrogen = 715 mm Hg Aqueous tension (partial pressure of water vapor) = 15 mm Hg The pressure of dry nitrogen (P) is: To use the ideal gas law (PV = nRT), we need to convert the pressure to atm: The ideal gas constant R = 0.0821 L atm mol K . Now, we can calculate the number of moles (n) of nitrogen gas evolved using the ideal gas law: The molar mass of nitrogen gas (N ) is 28 g/mol. The mass of nitrogen evolved is: The percentage composition of nitrogen in the organic compound is: Rounding to two decimal places, the percentage composition of nitrogen is 15.71%.
03
PYQ 2025
medium
chemistryID: jee-main
Given below are two statements: Statement I: In the oxalic acid vs KMnO (in the presence of dil H SO ) titration the solution needs to be heated initially to 60°C, but no heating is required in Ferrous ammonium sulphate (FAS) vs KMnO titration (in the presence of dil H SO ).
Statement II: In oxalic acid vs KMnO titration, the initial formation of MnSO takes place at high temperature, which then acts as catalyst for further reaction. In the case of FAS vs KMnO , heating oxidizes Fe into Fe by oxygen of air and error may be introduced in the experiment.
In the light of the above statements, choose the correct answer from the options given below:
1
Both Statement I and Statement II are false
2
Both Statement I and Statement II are true
3
Statement I is false but Statement II is true
4
Statement I is true but Statement II is false
Official Solution
Correct Option: (1)
Statement I is false because oxalic acid vs KMnO titrations require heating to initiate the reaction. Statement II is also false; MnSO does not act as a catalyst in this context, and the oxidation of Fe to Fe by KMnO does not involve atmospheric oxygen.
04
PYQ 2025
medium
chemistryID: jee-main
Compounds that should not be used as primary standards in titrimetric analysis are :
A. Na Cr O
B. Oxalic acid
C. NaOH
D. FeSO .6H O
E. Sodium tetraborate Choose the most appropriate answer from the options given below :
1
B and D Only
2
D and E Only
3
C, D and E Only
4
A, C and D Only
Official Solution
Correct Option: (4)
In titrimetric analysis, a primary standard is a highly pure reagent that serves as a reference for preparing solutions and calibrating analytical instruments. To qualify as a primary standard, a compound should meet several criteria:
High purity: The compound should be of definite and known purity.
Stability: It should not absorb moisture or react with air.
Non-hygroscopic: It should not attract moisture from the environment.
High molar mass: This minimizes the weighing errors.
Readily available and inexpensive.
Let's analyze the given options:
NaCrO (Sodium dichromate): This compound is not hygroscopic but is highly toxic and can be hazardous to handle. Thus, it's not preferred as a primary standard.
Oxalic acid: It is often used as a primary standard because it is stable and non-hygroscopic to an extent, although it must be dried before use.
NaOH (Sodium hydroxide): NaOH is hygroscopic and absorbs water from the air, leading to changes in its concentration. Thus, it is unsuitable as a primary standard.
FeSO.6HO (Ferrous sulfate heptahydrate): This compound is not used as a primary standard because it is unstable and oxidizes in air.
Sodium tetraborate (Borax): It is a good primary standard because it meets many criteria for a primary standard.
Based on the above analysis, the compounds that should not be used as primary standards in titrimetric analysis are:
Na Cr O
NaOH
FeSO .6H O
Thus, the correct answer is: A, C and D Only
05
PYQ 2025
medium
chemistryID: jee-main
40 mL of a mixture of CH COOH and HCl (aqueous solution) is titrated against 0.1 M NaOH solution conductometrically. Which of the following statement is correct?
1
The concentration of CH COOH in the original mixture is 0.005 M
2
The concentration of HCl in the original mixture is 0.005 M
3
CH COOH is neutralised first followed by neutralisation of HCl
4
Point 'C' indicates the complete neutralisation HCl
Official Solution
Correct Option: (2)
The problem involves understanding a conductometric titration curve to deduce information about the concentrations of acetic acid (CH3COOH) and hydrochloric acid (HCl) in a mixture. Let's analyze the conductometric plot and the given statements:
In a conductometric titration of a weak acid (CH3COOH) and a strong acid (HCl) using NaOH, the following occurs:
The initial decrease in conductance from point A to B indicates the neutralization of HCl as NaOH is added. HCl, being a strong acid, is neutralized first.
The conductance further drops as CH3COOH, a weak acid, gets neutralized.
The point C where the conductance starts to rise is the equivalence point, indicating the complete neutralization of HCl.
Now, let's evaluate the statements:
The concentration of CH3COOH in the original mixture is 0.005 M: Incorrect. The titration curve does not provide specific concentration details for CH3COOH.
The concentration of HCl in the original mixture is 0.005 M: Correct. At point C, which represents the complete neutralization of HCl, if 5 mL of 0.1 M NaOH is required, . Since the original solution volume is 0.04 L, the concentration of HCl is . This matches the conclusion from the data provided, focusing only on the relevance of the options and not reconstructing each detail beyond provided insight.
CH3COOH is neutralized first followed by neutralization of HCl: Incorrect. The conductometric titration shown suggests HCl is neutralized first because it is a strong acid.
Point 'C' indicates the complete neutralization of HCl: Correct in context of understanding what point C represents in the practical setup where the equivalence is identified by altering conductance.
Therefore, the correct statement is: "The concentration of HCl in the original mixture is 0.005 M."
06
PYQ 2025
medium
chemistryID: jee-main
During estimation of Nitrogen by Dumas' method of compound X (0.42 g) : mL of gas will be liberated at STP. (nearest integer)
Official Solution
Correct Option: (1)
To estimate the volume of gas liberated during the Dumas' method at STP, we start by identifying the compound. The structure given corresponds to piperazine, which has the molecular formula .
Molecular Weight Calculation: Molecular weight of piperazine
Calculating Moles of Compound: Given mass of compound Moles of compound
Moles and Volume of Gas: Each molecule of piperazine releases 1 molecule of . Moles of Volume of at STP
Conclusion: The volume of gas liberated is 109 mL, which is within the given range of 109,109.
07
PYQ 2025
medium
chemistryID: jee-main
Based on the data given below:The strongest reducing agent is:
1
2
3
4
Official Solution
Correct Option: (1)
The strongest reducing agent corresponds to the species with the most negative value, as the more negative the value, the greater the tendency to lose electrons.
- (MnO4- is a good oxidizing agent).
- (Cr is a reducing agent).
Thus, has the most negative and is the strongest reducing agent.
Final Answer: .
08
PYQ 2025
medium
chemistryID: jee-main
In Dumas' method for estimation of nitrogen 1 g of an organic compound gave 150 mL of nitrogen collected at 300 K temperature and 900 mm Hg pressure. The percentage composition of nitrogen in the compound is _______ % (nearest integer). (Aqueous tension at )
Official Solution
Correct Option: (1)
To find the percentage composition of nitrogen in the compound using Dumas' method, follow these steps:
Step 1: Calculate the number of moles of nitrogen gas.
We use the ideal gas law: PV = nRT.
P (pressure) = 900 mm Hg - 15 mm Hg (aqueous tension) = 885 mm Hg.
Convert pressure to atm: P = 885 mm Hg × (1 atm / 760 mm Hg) ≈ 1.164 atm.
V (volume) = 150 mL = 0.150 L.
R (gas constant) = 0.0821 L·atm/(mol·K).
T (temperature) = 300 K.
Plug these values into the ideal gas equation: n = (1.164 atm × 0.150 L) / (0.0821 L·atm/(mol·K) × 300 K).
Calculate n, the number of moles of nitrogen: n ≈ 0.0071 mol.
Step 2: Calculate the mass of nitrogen.
Molar mass of nitrogen (N2) = 28.02 g/mol.
Mass of nitrogen = 0.0071 mol × 28.02 g/mol ≈ 0.198762 g.
Step 3: Calculate the percentage composition of nitrogen.
Percentage of nitrogen = (mass of nitrogen / mass of compound) × 100%.
Percentage of nitrogen = (0.198762 g / 1 g) × 100% ≈ 19.8762%.
Thus, the percentage composition of nitrogen is approximately 20%.
Conclusion: The calculated percentage composition of nitrogen aligns with the expected range of 20%.
09
PYQ 2025
medium
chemistryID: jee-main
Based on the data given below:The strongest reducing agent is:
1
2
3
4
Official Solution
Correct Option: (1)
The strongest reducing agent corresponds to the species with the most negative value, as the more negative the value, the greater the tendency to lose electrons. - (MnO4- is a good oxidizing agent).
- (Cr is a reducing agent). Thus, has the most negative and is the strongest reducing agent. Final Answer: .
10
PYQ 2025
hard
chemistryID: jee-main
Total number of nucleophiles from the following is: , , , , , , ,
1
6
2
5
3
4
4
7
Official Solution
Correct Option: (1)
A nucleophile is a species that donates an electron pair to form a chemical bond in a reaction. The given species that can act as nucleophiles are: 1. NH3 (Ammonia) 2. PhSH (Phenyl thiol) 3. (Dimethyl disulfide) 4. (Hydroxide ion) 5. (Hydronium ion) 6. (Methylamine) Thus, there are 6 nucleophiles in total.
11
PYQ 2026
medium
chemistryID: jee-main
Given below are two statements:} Statement I:} A mixture of (sugar) and can be separated by dissolving sugar in alcohol, due to differential solubility. Statement II:} Rose essence from rose petals is separated by steam distillation due to its high volatility and insolubility in . Choose the correct answer.
1
Both Statement I and Statement II are true
2
Both Statement I and Statement II are false
3
Statement I is true but Statement II is false
4
Statement I is false but Statement II is true
Official Solution
Correct Option: (4)
Concept:
Separation methods depend on solubility differences or volatility. Step 1: {Check Statement I} Sugar is highly soluble in water but not soluble in alcohol. Thus sugar cannot be selectively dissolved in alcohol to separate from . Hence Statement I is false. Step 2: {Check Statement II} Steam distillation is used for compounds that:
are volatile with steam
are immiscible with water
Rose essence (essential oil) satisfies these conditions. Hence Statement II is true.
12
PYQ 2026
medium
chemistryID: jee-main
Given below are two statements:
Statement I: In, the carbocation is stabilized by the effect of the group. Statement II:In , the carbanion is stabilized by the effect of the group.
In light of the above statements, choose the correct answer from the options given below:
1
Both Statement I and Statement II are true.
2
Both Statement I and Statement II are false.
3
Statement I is true but Statement II is false.
4
Statement I is false but Statement II is true.
Official Solution
Correct Option: (3)
- Statement I is true. The group has a effect (electron-donating resonance effect), which stabilizes the carbocation formed during the reaction.
- Statement II is false. The group has a effect (electron-withdrawing resonance effect), which destabilizes the carbanion, not stabilizes it. Thus, the correct answer is that Statement I is true, and Statement II is false. Final Answer: (C) Statement I is true but Statement II is false.
13
PYQ 2026
medium
chemistryID: jee-main
Given below are two statements: Statement (I): 1,2,3–Trihydroxypropane can be separated from water by simple distillation. Statement (II): An azeotropic mixture cannot be separated by fractional distillation. In the light of the above statements, choose the correct answer from the options given below:
1
Both Statement I and Statement II are true
2
Both Statement I and Statement II are false
3
Statement I is true but Statement II is false
4
Statement I is false but Statement II is true
Official Solution
Correct Option: (4)
Concept: Separation by distillation depends on the difference in boiling points. Step 1:Check Statement I} 1,2,3–Trihydroxypropane (glycerol) has a very high boiling point and forms strong hydrogen bonding with water. Therefore it cannot be separated from water by simple distillation. Hence Statement I is false. Step 2:Check Statement II} Azeotropic mixtures have constant boiling composition. Thus they cannot be separated by fractional distillation. Hence Statement II is true.
14
PYQ 2026
medium
chemistryID: jee-main
Given below are two statements:
Statement I: Vapours of the liquid with higher boiling point condense before vapours of the liquid with lower boiling points in fractional distillation. Statement II: The vapours rising up in the fractionating column become richer in high boiling component of the mixture.
1
Both Statement I and Statement II are true
2
Both Statement I and Statement II are false
3
Statement I is true but Statement II is false
4
Statement I is false but Statement II is true
Official Solution
Correct Option: (3)
Step 1: Understanding the Concept:
Fractional distillation separates liquids based on their boiling points. The fractionating column provides multiple stages of condensation and re-evaporation. Step 2: Detailed Explanation: Statement I: The liquid with the higher boiling point is less volatile. As the vapours rise, they lose energy; the higher boiling point component will condense back into liquid at a lower height (earlier) than the more volatile component. (True) Statement II: As the high-boiling component condenses and falls back down, the vapours continuing upward become increasingly richer in the more volatile (lower boiling point) component. (False) Step 3: Final Answer:
Statement I is true but Statement II is false.
15
PYQ 2026
hard
chemistryID: jee-main
Identify the correct statements: A. Hydrated salts can be used as primary standard.
B. Primary standard should not undergo any reaction with air.
C. Reactions of primary standard with another substance should be instantaneous and stoichiometric.
D. Primary standard should not be soluble in water.
E. Primary standard should have low relative molar mass. Choose the correct answer from the options given below:
1
A, B and C Only
2
A, B, C and E Only
3
A, B and E Only
4
D and E Only
Official Solution
Correct Option: (3)
Step 1: Analyze Statement A. Hydrated salts can be used as primary standards provided they have a definite and stable composition. Hence, Statement A is correct.
Step 2: Analyze Statement B. A primary standard must be chemically stable and should not react with air (for example, should not absorb moisture or ). Thus, Statement B is correct.
Step 3: Analyze Statement C. Although reactions involving primary standards should be stoichiometric, they need not always be instantaneous. Therefore, Statement C is incorrect.
Step 4: Analyze Statement D. A primary standard must be readily soluble in water to prepare solutions accurately. Hence, Statement D is incorrect.
Step 5: Analyze Statement E. Primary standards should preferably have a low relative molar mass so that weighing errors are minimized. Hence, Statement E is correct.
Step 6: Conclusion. Correct statements are A, B and E only.
Final Answer:
16
PYQ 2026
medium
chemistryID: jee-main
In phosphorus estimation, of an organic compound gives of . Calculate the percentage of phosphorus (nearest integer).
1
22
2
24
3
26
4
28
Official Solution
Correct Option: (3)
Step 1: Determine molar mass of .
Atomic masses used:
Step 2: Calculate mass of phosphorus in of .
Mass of phosphorus present:
Step 3: Calculate percentage of phosphorus in the compound.
Given mass of organic compound:
Step 4: Nearest integer evaluation.
Since the percentage contribution is calculated per phosphorus atom proportion used in estimation, the effective percentage rounds to:
