### Related Formula textNa_2textS + textNa_2[textFe(textCN)_5textNO] rightarrow textNa_4[textFe(textCN)_5textNOS]$\text{Na}_2\text{S} + \text{Na}_2[\text{Fe}(\text{CN})_5\text{NO}] \rightarrow \text{Na}_4[\text{Fe}(\text{CN})_5\text{NOS}]$ AI responses may include mistakes. ### Core Logic Sulphide ion (S^2-$S^{2-}$) undergoes a qualitative verification test when reacted with sodium nitroprusside. Sodium extract of the salt containing sulphide forms sodium sulphide (mathrmNa_2S$\mathrm{Na_2S}$). 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]$\mathrm{Na_2S + Na_2[Fe(CN)_5NO] \rightarrow Na_4[Fe(CN)_5NOS]}$ ### Step 1: Verification This specific purple/violet reaction occurs exclusively for the identification of the **Sulphide ion** (S^2-$S^{2-}$). ### 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

### Related Formula Precipitation equations matching standard analytical profiles: mathrm2Cu^2+ + [Fe(CN)_6]^4- rightarrow Cu_2[Fe(CN)_6] downarrow \ (Chocolate\ Brown)$\mathrm{2Cu^{2+} + [Fe(CN)_6]^{4-} \rightarrow Cu_2[Fe(CN)_6] \downarrow \ (Chocolate\ Brown)}$ mathrm4Fe^3+ + 3[Fe(CN)_6]^4- rightarrow Fe_4[Fe(CN)_6]_3 downarrow \ (Prussian\ Blue)$\mathrm{4Fe^{3+} + 3[Fe(CN)_6]^{4-} \rightarrow Fe_4[Fe(CN)_6]_3 \downarrow \ (Prussian\ Blue)}$ ### Core Logic Let's examine each analytical chemistry reaction step row-by-row: * **Reaction (A)** produces mathrmCu_2[Fe(CN)_6]$\mathrm{Cu_2[Fe(CN)_6]}$, confirming a chocolate brown residue profile (Correct). * **Reaction (B)** forms complex mathrmFe_4[Fe(CN)_6]_3$\mathrm{Fe_4[Fe(CN)_6]_3}$, yielding Prussian Blue coloration (Correct). * **Reaction (C)** yields potassium zinc ferrocyanide matrix mathrmK_2Zn_3[Fe(CN)_6]_2$\mathrm{K_2Zn_3[Fe(CN)_6]_2}$, 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]$\mathrm{K_4[Fe(CN)_6]}$ 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

### 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$\mathrm{Na}_2\mathrm{Cr}_2\mathrm{O}_7$: Highly hygroscopic (unlike mathrmK_2mathrmCr_2mathrmO_7$\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$), absorbs water from air, composition varies rightarrow$\rightarrow$ *Cannot be used*. - Oxalic acid: Highly stable, non-hygroscopic, definite composition rightarrow$\rightarrow$ *Can be used*. - mathrmNaOH$\mathrm{NaOH}$: Extremely hygroscopic, absorbs moisture and mathrmCO_2$\mathrm{CO}_2$ from air rightarrow$\rightarrow$ *Cannot be used*. - mathrmFeSO_4 cdot 6mathrmH_2mathrmO$\mathrm{FeSO}_4 \cdot 6\mathrm{H}_2\mathrm{O}$: Easily oxidized by air, unstable composition rightarrow$\rightarrow$ *Cannot be used*. - Sodium tetraborate (Borax): Highly stable, clear hydration state rightarrow$\rightarrow$ *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$\mathrm{Na}_2\mathrm{Cr}_2\mathrm{O}_7$) are highly hygroscopic, whereas potassium di-chromate (mathrmK_2mathrmCr_2mathrmO_7$\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$) is non-hygroscopic and works as an excellent primary standard. Deliquescent bases like mathrmNaOH$\mathrm{NaOH}$ 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