Compounds that should not be used as primary standards in titrimetric analysis are: A. mathrmNa_2mathrmCr_2mathrmO_7 B. Oxalic acid C. mathrmNaOH D. mathrmFeSO_4 cdot 6mathrmH_2mathrmO E. Sodium tetraborate Choose the most appropriate answer from the options given below:

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: - mathrmNa_2mathrmCr_2mathrmO_7: Highly hygroscopic (unlike mathrmK_2mathrmCr_2mathrmO_7), absorbs water from air, composition varies rightarrow *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition rightarrow *Can be used*. - mathrmNaOH: Extremely hygroscopic, absorbs moisture and mathrmCO_2 from air rightarrow *Cannot be used*. - mathrmFeSO_4 cdot 6mathrmH_2mathrmO: Easily oxidized by air, unstable composition rightarrow *Cannot be used*. - Sodium tetraborate (Borax): Highly stable, clear hydration state 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 (mathrmNa_2mathrmCr_2mathrmO_7) are highly hygroscopic, whereas potassium di-chromate (mathrmK_2mathrmCr_2mathrmO_7) is non-hygroscopic and works as an excellent primary standard. Deliquescent bases like mathrmNaOH and easily oxidized transition metal salts like Mohr's salt counterparts can never serve as primary standards. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Practical Chemistry

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Q jee_main_2025_02_april_evening Qualitative Analysis of Anions
Formation of mathrmNa_4[mathrmFe(mathrmCN)_5mathrmNOS], a purple coloured complex formed by addition of sodium nitroprusside in sodium carbonate extract of salt indicates the presence of:
  • A. textSodium ion
  • B. textSulphate ion
  • C. textSulphide ion
  • D. textSulphite ion

Solution

### Related Formula textNa_2textS + textNa_2[textFe(textCN)_5textNO] rightarrow textNa_4[textFe(textCN)_5textNOS] AI responses may include mistakes. ### Core Logic Sulphide ion (S^2-) undergoes a qualitative verification test when reacted with sodium nitroprusside. Sodium extract of the salt containing sulphide forms sodium sulphide (mathrmNa_2S). When sodium nitroprusside solution is added to the sodium carbonate extract, the sulphide reacts to yield a deep violet/purple coloured complex called sodium thionitroprusside: mathrmNa_2S + Na_2[Fe(CN)_5NO] rightarrow Na_4[Fe(CN)_5NOS] ### Step 1: Verification This specific purple/violet reaction occurs exclusively for the identification of the **Sulphide ion** (S^2-). ### Pattern Recognition Mnemonic: 'Nitroprusside turns purple for Sulphide'. This is a highly specific redox/substitution reaction of coordination complexes used inside analytical laboratory practices. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Practical Chemistry
Q41 jee_main_2025_02_april_morning Qualitative Salt Analysis Reactions
Choose the correct tests with respective observations. (A) mathrmCuSO_4 (acidified with acetic acid) + mathrmK_4[mathrmFe(mathrmCN)_6] rightarrow Chocolate brown precipitate. (B) mathrmFeCl_3 + mathrmK_4[mathrmFe(mathrmCN)_6] rightarrow Prussian blue precipitate. (C) mathrmZnCl_2 + mathrmK_4[mathrmFe(mathrmCN)_6], neutralised with mathrmNH_4mathrmOH rightarrow mathrmWhite or bluish white precipitate. (D) mathrmMgCl_2 + mathrmK_4[mathrmFe(mathrmCN)_6] rightarrow mathrmBlue precipitate. (E) mathrmBaCl_2 + mathrmK_4[mathrmFe(mathrmCN)_6], neutralised with mathrmNaOH rightarrow mathrmWhite precipitate. Choose the correct answer from the options given below:
  • A. text(1) A, D and E only
  • B. text(2) B, D and E only
  • C. text(3) A, B and C only
  • D. text(4) C, D and E only

Solution

### Related Formula Precipitation equations matching standard analytical profiles: mathrm2Cu^2+ + [Fe(CN)_6]^4- rightarrow Cu_2[Fe(CN)_6] downarrow \ (Chocolate\ Brown) mathrm4Fe^3+ + 3[Fe(CN)_6]^4- rightarrow Fe_4[Fe(CN)_6]_3 downarrow \ (Prussian\ Blue) ### Core Logic Let's examine each analytical chemistry reaction step row-by-row: * **Reaction (A)** produces mathrmCu_2[Fe(CN)_6], confirming a chocolate brown residue profile (Correct). * **Reaction (B)** forms complex mathrmFe_4[Fe(CN)_6]_3, yielding Prussian Blue coloration (Correct). * **Reaction (C)** yields potassium zinc ferrocyanide matrix mathrmK_2Zn_3[Fe(CN)_6]_2, appearing as a white or bluish-white solid precipitate (Correct). * **Reactions (D) & (E)** do not form the described colored precipitates with this reagent under regular analytical configurations. ### Step 1: Selection Thus, only tests A, B, and C provide correct observations. ### Pattern Recognition Potassium ferrocyanide mathrmK_4[Fe(CN)_6] is a vital reagent for identifying transition metal cations. Note the specific colors: Copper yields chocolate brown, Iron(III) gives Prussian blue, and Zinc forms a white solid. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Practical Chemistry Class 12 Chemistry: Coordination Compounds
Q49 jee_main_2025_24_jan_morning Qualitative Analysis of Cations
Among the following cations, the number of cations which will give characteristic precipitate in their identification tests with mathrmK_4[mathrmFe(mathrmCN)_6] is: mathrmCu^2+ , mathrmFe^3+ , mathrmBa^2+ , mathrmCa^2+ , mathrmNH_4^+ , mathrmMg^2+ , mathrmZn^2+
Numerical Answer. Answer: 3 to 3

Solution

### Core Logic Potassium ferrocyanide, K_4[Fe(CN)_6], serves as a key reagent for identifying specific metal cations via diagnostic precipitation reactions: - Cu^2+ yields a characteristic chocolate-brown precipitate: Cu_2[Fe(CN)_6]. - Fe^3+ reacts to produce an intense Prussian blue precipitate: Fe_4[Fe(CN)_6]_3. - Zn^2+ forms a distinct white/grey-white precipitate: Zn_2[Fe(CN)_6]. *(Note: While Ca^2+ can form a complex under specific concentrated conditions, standard qualitative test protocols map the primary distinct precipitates to **3** principal metals).* Therefore, the final integer count is **3**. ### Pattern Recognition Remember the classic color transformations for ferrocyanide tests: copper shifts to chocolate brown, while iron transforms into Prussian blue. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Practical Chemistry
Q83 jee_main_2024_01_february_morning Qualitative Analysis
The number of white coloured salts among the following is .... (a) SrSO_4 (b) Mg(NH_4)PO_4 (c) BaCrO_4 (d) Mn(OH)_2 (e) PbSO_4 (f) PbCrO_4 (g) AgBr (h) PbI_2 (i) CaC_2O_4 (j) [Fe(OH)_2(CH_3COO)]
Numerical Answer. Answer: 5 to 5

Solution

### Core Logic Analyzing the colors of the given precipitates/salts from qualitative analysis: (a) SrSO_4 - White precipitate (Group V/Sulfates) (b) Mg(NH_4)PO_4 - White crystalline precipitate (Group VI test for Mg) (c) BaCrO_4 - Yellow precipitate (Test for Barium) (d) Mn(OH)_2 - White precipitate (turns brown on standing due to oxidation to MnO_2) (e) PbSO_4 - White precipitate (Group I / Sulfates) (f) PbCrO_4 - Yellow precipitate (Chrome yellow) (g) AgBr - Pale yellow precipitate (h) PbI_2 - Yellow precipitate (Golden spangles) (i) CaC_2O_4 - White precipitate (Calcium oxalate) (j) [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: 1. SrSO_4 2. Mg(NH_4)PO_4 3. Mn(OH)_2 4. PbSO_4 5. 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 (BaCrO_4, PbCrO_4) are distinctly yellow. Silver halides range from white (AgCl) to pale yellow (AgBr) to yellow (AgI). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Principles Related to Practical Chemistry Class 12 Chemistry: The d-and f-Block Elements

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