Compounds that should not be used as primary standards in titrimetric analysis are: A. Na2Cr2O7 B. Oxalic acid C. NaOH D. FeSO4 cdot 6H2O E. Sodium tetraborate Choose the most appropriate answer from the options given below:

A primary standard is a highly pure, stable chemical substance with a known, definite composition that can be directly weighed. It must not be hygroscopic, deliquescent, or easily oxidized by air. Evaluate each substance: - Na2Cr2O7: Highly hygroscopic (unlike K2Cr2O7), absorbs water from air, composition varies arrow *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition arrow *Can be used*. - NaOH: Extremely hygroscopic, absorbs moisture and CO2 from air arrow *Cannot be used*. - FeSO4 cdot 6H2O: Easily oxidized by air, unstable composition arrow *Cannot be used*. - Sodium tetraborate (Borax): Highly stable, clear hydration state arrow *Can be used*. The compounds that should *not* be used are A, C, and D. This corresponds to Option (4). Sodium salts of di-chromate (Na2Cr2O7) are highly hygroscopic, whereas potassium di-chromate (K2Cr2O7) is non-hygroscopic and works as an excellent primary standard. Deliquescent bases like NaOH and easily oxidized transition metal salts like Mohr's salt counterparts can never serve as primary standards. Class 11 Chemistry: Practical Chemistry

Compounds that should not be used as primary standards in titrimetric analysis are: A. Na2Cr2O7 B. Oxalic acid C. NaOH D. FeSO4 cdot 6H2O E. Sodium tetraborate Choose the most appropriate answer from

A primary standard is a highly pure, stable chemical substance with a known, definite composition that can be directly weighed. It must not be hygroscopic, deliquescent, or easily oxidized by air. Evaluate each substance: - Na2Cr2O7: Highly hygroscopic (unlike K2Cr2O7), absorbs water from air, composition varies arrow *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition arrow *Can be used*. - NaOH: Extremely hygroscopic, absorbs moisture and CO2 from air arrow *C

Compounds that should not be used as primary standards in titrimetric analysis are: A. Na2Cr2O7 B. Oxalic acid C. NaOH D. FeSO4 cdot 6H2O E. Sodium tetraborate Choose the most appropriate answer from the options given below:

A primary standard is a highly pure, stable chemical substance with a known, definite composition that can be directly weighed. It must not be hygroscopic, deliquescent, or easily oxidized by air. Evaluate each substance: - Na2Cr2O7: Highly hygroscopic (unlike K2Cr2O7), absorbs water from air, composition varies arrow *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition arrow *Can be used*. - NaOH: Extremely hygroscopic, absorbs moisture and CO2 from air arrow *Cannot be used*. - FeSO4 cdot 6H2O: Easily oxidized by air, unstable composition arrow *Cannot be used*. - Sodium tetraborate (Borax): Highly stable, clear hydration state arrow *Can be used*. The compounds that should *not* be used are A, C, and D. This corresponds to Option (4). Sodium salts of di-chromate (Na2Cr2O7) are highly hygroscopic, whereas potassium di-chromate (K2Cr2O7) is non-hygroscopic and works as an excellent primary standard. Deliquescent bases like NaOH and easily oxidized transition metal salts like Mohr's salt counterparts can never serve as primary standards. Class 11 Chemistry: Practical Chemistry

Compounds that should not be used as primary standards in titrimetric analysis are: A. Na2Cr2O7 B. Oxalic acid C. NaOH D. FeSO4 cdot 6H2O E. Sodium tetraborate Choose the most appropriate answer from

A primary standard is a highly pure, stable chemical substance with a known, definite composition that can be directly weighed. It must not be hygroscopic, deliquescent, or easily oxidized by air. Evaluate each substance: - Na2Cr2O7: Highly hygroscopic (unlike K2Cr2O7), absorbs water from air, composition varies arrow *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition arrow *Can be used*. - NaOH: Extremely hygroscopic, absorbs moisture and CO2 from air arrow *C

Compounds that should not be used as primary standards in titrimetric analysis are: A. Na2Cr2O7 B. Oxalic acid C. NaOH…

Year	2026	2025	2024	Total
Questions	1	4	3	8

Year

2026

2025

2024

Total

Questions

Solution & Explanation

Related Formula

A primary standard is a highly pure, stable chemical substance with a known, definite composition that can be directly weighed. It must not be hygroscopic, deliquescent, or easily oxidized by air.

Core Logic

Evaluate each substance:

$Na₂Cr₂O₇$ : Highly hygroscopic (unlike $K₂Cr₂O₇$ $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$), absorbs water from air, composition varies $arrow$ $\rightarrow$ Cannot be used.
Oxalic acid: Highly stable, non-hygroscopic, definite composition $arrow$ $\rightarrow$ Can be used.
$NaOH$ $\mathrm{NaOH}$: Extremely hygroscopic, absorbs moisture and $CO₂$ $\mathrm{CO}_2$ from air $arrow$ $\rightarrow$ Cannot be used.
$FeSO₄ \cdot 6H₂O$ : Easily oxidized by air, unstable composition $arrow$ $\rightarrow$ Cannot be used.
Sodium tetraborate (Borax): Highly stable, clear hydration state $arrow$ $\rightarrow$ Can be used.

Step 1: Select incorrect standards

The compounds that should not be used are A, C, and D. This corresponds to Option (4).

Pattern Recognition

Sodium salts of di-chromate ( $Na₂Cr₂O₇$ ) are highly hygroscopic, whereas potassium di-chromate ( $K₂Cr₂O₇$ $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$) is non-hygroscopic and works as an excellent primary standard. Deliquescent bases like $NaOH$ $\mathrm{NaOH}$ and easily oxidized transition metal salts like Mohr's salt counterparts can never serve as primary standards.

Chapter Mix

Class 11 Chemistry: Practical Chemistry

More Practical Chemistry Previous-Year Questions — Page 2

Q83 jee_main_2024_01_february_morning Qualitative Analysis

The number of white coloured salts among the following is .... (a)

SrSO₄

(b)

Mg(NH₄)PO₄

(c)

BaCrO₄

(d)

Mn(OH)₂

(e)

PbSO₄

(f)

PbCrO₄

(g)

AgBr

(h)

PbI₂

(i)

CaC₂O₄

(j)

[Fe(OH)₂(CH₃COO)]

Numerical Answer. Answer: 5 to 5

Solution

Core Logic

Analyzing the colors of the given precipitates/salts from qualitative analysis: (a) $SrSO₄$ $SrSO_4$ - White precipitate (Group V/Sulfates) (b) $Mg(NH₄)PO₄$ $Mg(NH_4)PO_4$ - White crystalline precipitate (Group VI test for Mg) (c) $BaCrO₄$ $BaCrO_4$ - Yellow precipitate (Test for Barium) (d) $Mn(OH)₂$ $Mn(OH)_2$ - White precipitate (turns brown on standing due to oxidation to $MnO₂$ $MnO_2$) (e) $PbSO₄$ $PbSO_4$ - White precipitate (Group I / Sulfates) (f) $PbCrO₄$ $PbCrO_4$ - Yellow precipitate (Chrome yellow) (g) $AgBr$ $AgBr$ - Pale yellow precipitate (h) $PbI₂$ $PbI_2$ - Yellow precipitate (Golden spangles) (i) $CaC₂O₄$ $CaC_2O_4$ - White precipitate (Calcium oxalate) (j) $[Fe(OH)₂(CH₃COO)]$ $[Fe(OH)_2(CH_3COO)]$ - Blood red / Brown red coloration (Basic iron acetate, acetate radical test)

Step 1: Count White Salts

The salts that are white are:

$SrSO₄$ $SrSO_4$
$Mg(NH₄)PO₄$ $Mg(NH_4)PO_4$
$Mn(OH)₂$ $Mn(OH)_2$
$PbSO₄$ $PbSO_4$
$CaC₂O₄$ $CaC_2O_4$

Total count = 5.

Pattern Recognition

Most alkali/alkaline-earth metal salts (sulfates, oxalates, phosphates) and lead(II) sulfate/chloride are white. Chromates ( $BaCrO₄$ $BaCrO_4$, $PbCrO₄$ $PbCrO_4$) are distinctly yellow. Silver halides range from white ( $AgCl$ $AgCl$) to pale yellow ( $AgBr$ $AgBr$) to yellow ( $AgI$ $AgI$).

Chapter Mix

Class 11 Chemistry: Principles Related to Practical Chemistry Class 12 Chemistry: The d-and f-Block Elements

Q jee_main_2024_29_january_evening Chromatographic Separations

Chromatographic technique/s based on the principle of differential adsorption is/are A. Column chromatography B. Thin layer chromatography C. Paper chromatography Choose the most appropriate answer from the options given below:

A. B only
B. A only
C. A & B only
D. C only

Solution

Related Formula

Classification of chromatography based on adsorption vs partition parameters.

Core Logic

Chromatography techniques are broadly divided into two main categories based on their operating principles:

Adsorption Chromatography: Relies on the differential adsorption of components on the surface of a stationary phase. Both Column Chromatography and Thin Layer Chromatography (TLC) operate on this principle.
Partition Chromatography: Relies on continuous differential partitioning of components between stationary and mobile liquid phases. Paper Chromatography is a prime example of this category.

Step 1: Final Selection

Thus, statements A and B are correct, matching choice (3).

Pattern Recognition

Remember: Column and Thin Layer chromatography are adsorption-based, while paper chromatography relies on partition mechanisms.

Chapter Mix

Class 11 Chemistry: Principles of Practical Chemistry

Q87 jee_main_2024_29_jan_morning Organic Functional Groups

Number of compounds among the following which contain sulphur as heteroatom is Furan, Thiophene, Pyridine, Pyrrole, Cysteine, Tyrosine

Numerical Answer. Answer: 2 to 2

Solution

Core Logic

Let us check the chemical structure of each compound given in the list to determine if it contains a Sulphur (S) atom.

Furan: A 5-membered heterocyclic aromatic ring containing Oxygen ( $C₄H₄O$ $C_4H_4O$). No Sulphur.
Thiophene: A 5-membered heterocyclic aromatic ring containing Sulphur ( $C₄H₄S$ $C_4H_4S$). Contains Sulphur.
Pyridine: A 6-membered heterocyclic aromatic ring containing Nitrogen ( $C₅H₅N$ $C_5H_5N$). No Sulphur.
Pyrrole: A 5-membered heterocyclic aromatic ring containing Nitrogen ( $C₄H₄NH$ $C_4H_4NH$). No Sulphur.
Cysteine: A naturally occurring $α$ $\alpha$-amino acid with a thiol side chain ( $-CH₂-SH$ $-CH_2-SH$). Contains Sulphur.
Tyrosine: An $α$ $\alpha$-amino acid with a phenol side chain. No Sulphur.

Step 1: Final Count

Organic Functional Groups diagram for Q87 - JEE Main 2024 Morning

Only Thiophene and Cysteine contain a sulphur heteroatom. Total number = 2.

Chapter Mix

Class 11 Chemistry: Organic Chemistry Some Basic Principles and Techniques Class 12 Chemistry: Biomolecules

Compounds that should not be used as primary standards in titrimetric analysis are: A. $Na₂Cr₂O₇$ B. Oxalic acid C. $NaOH$ $\mathrm{NaOH}$ D. $FeSO₄ \cdot 6H₂O$ E. Sodium tetraborate Choose the most appropriate answer from the options given below:

Solution & Explanation

Related Formula

Core Logic

Step 1: Select incorrect standards

Pattern Recognition

Chapter Mix

Reference Study Guides

More Practical Chemistry Previous-Year Questions — Page 2

Solution

Core Logic

Step 1: Count White Salts

Pattern Recognition

Chapter Mix

Solution

Related Formula

Core Logic

Step 1: Final Selection

Pattern Recognition

Chapter Mix

Solution

Core Logic

Step 1: Final Count

Chapter Mix

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Solution & Explanation

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Core Logic

Step 1: Select incorrect standards

Pattern Recognition

Chapter Mix

Reference Study Guides

More Practical Chemistry Previous-Year Questions — Page 2

Solution

Core Logic

Step 1: Count White Salts

Pattern Recognition

Chapter Mix

Solution

Related Formula

Core Logic

Step 1: Final Selection

Pattern Recognition

Chapter Mix

Solution

Core Logic

Step 1: Final Count

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