Chapter 31

While titrating dilute \(\mathrm{HCl}\) solution with aqueous \(\mathrm{NaOH}\), which of the following will not be required? (a) Burette and porcelain tile (b) Pipette and distilled water (c) Clamp and phenolphthalein (d) Bunsen burner and measuring cylinder

If you spill a chemical toilet cleaning liquid on your hand, your first aid would be : (a) vinegar (b) aqueous \(\mathrm{NaOH}\) (c) aqueous \(\mathrm{NaHCO}_{3}\) (d) aqueous \(\mathrm{NH}_{3}\)

The Kjeldahl method of Nitrogen estimation fails for which of the following reaction products? (1) O=[N+]([O-])c1ccccc1 \(\mathrm{Sn} / \mathrm{HCl}\) (2) N#Cc1ccccc1 \(\mathrm{AlH}_{4}\) (3) N#CCc1ccccc1 Nc1ccccc1 (4) \(\|_{\mathrm{HCl}}^{\mathrm{NaNO}_{2}} \underset{\mathrm{H} l}{\frac{\mathrm{NaN}}{\longrightarrow}}\) (a) (3) and (4) (b) (1) and (4) (c) (1), (3) and (4) (d) \((2)\) and \((3)\)

The strength of an aqueous \(\mathrm{NaOH}\) solution is most accurately determined by titrating: (Note: consider that an appropriate indicator is used) (a) Aq. \(\mathrm{NaOH}\) in a pipette and aqueous oxalic acid in a burette (b) Aq. \(\mathrm{NaOH}\) in a burette and aqueous oxalic acid in a conical flask (c) Aq. \(\mathrm{NaOH}\) in a burette and concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in a conical flask (d) Aq. \(\mathrm{NaOH}\) in a volumetric flask and concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in a conical flask

Sodium metal on dissolution in liquid ammonia gives a deep blue solution due to the formation of: (a) sodium-ammonia complex (b) sodamide (c) sodium ion-ammonia complex (d) ammoniated electrons

The green colour produced in the borax bead test of a chromium (III) salt is due to (a) \(\mathrm{Cr}_{2}\left(\mathrm{~B}_{4} \mathrm{O}_{7}\right)_{3}\) (b) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{Cr}\left(\mathrm{BO}_{2}\right)_{3}\) (d) \(\mathrm{CrB}\)

Kjeldahl's method cannot be used to estimate nitrogen for which of the following compounds? (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{C} \square \mathrm{N}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2}\) (d) NC(N)=O

For standardizing \(\mathrm{NaOH}\) solution, which of the following is used as a primary standard? (a) Sodium tetraborate (b) Ferrous ammonium sulfate (c) Oxalic acid (d) dil. HCl

A solution of \(m\)-chloroaniline, \(m\)-chlorophenol and \(m\)-chlorobenzoic acid in ethyl acetate was extracted initially with a saturated solution of \(\mathrm{NaHCO}_{3}\) to give fraction \(A\). The left over organic phase was extracted with dilute \(\mathrm{NaOH}\) solution to give fraction \(B\). The final organic layer was labelled as fraction \(C\). Fractions \(A, B\) and \(C\), contain respectively: (a) \(m\)-chlorobenzoic acid, \(m\)-chloroaniline and \(m\)-chlorophenol (b) \(m\)-chlorobenzoic acid, \(m\)-chlorophenol and \(m\)-chloroaniline (c) \(m\)-chlorophenol, \(m\)-chlorobenzoic acid and \(m\)-chloroaniline (d) \(m\)-chloroaniline, \(m\)-chlorobenzoic acid and \(m\)-chlorophenol

A solution containing a group-IV cation gives a precipitate on passing \(\mathrm{H}_{2} \mathrm{~S}\). A solution of this precipitate in dil.HCl produces a white precipitate with \(\mathrm{NaOH}\) solution and bluish-white precipitate with basic potassium ferrocyanide. The cation is : (a) \(\mathrm{Co}^{2+}\) (b) \(\mathrm{Ni}^{2+}\) (c) \(\mathrm{Mn}^{2+}\) (d) \(\mathrm{Zn}^{2+}\)

A chromatography column, packed with silica gel as stationary phase, was used to separate a mixture of compounds consisting of (A) benzanilide (B) aniline and (C) acetophenone. When the column is eluted with a mixture of solvents, hexane: ethyl acetate \((20: 80)\), the sequence of obtained compounds is: (a) (B), (C) and (A) (b) (B), (A) and (C) (c) (C), (A) and (B) (d) (A), (B) and (C)

The cation that will not be precipitated by \(\mathrm{H}_{2} \mathrm{~S}\) in the presence of dil. \(\mathrm{HCl}\) is : (a) \(\mathrm{Pb}^{2+}\) (b) \(\mathrm{Cu}^{2+}\) (c) \(\mathrm{Co}^{2+}\) (d) \(\mathrm{As}^{3+}\)

An organic compound ' \(A\) ' is oxidized with \(\mathrm{Na}_{2} \mathrm{O}_{2}\) followed by boiling with \(\mathrm{HNO}_{3}\). The resultant solution is then treated with ammonium molybdate to yield a yellow precipitate. Based on above observation, the element present in the given compound is: (a) Nitrogen (b) Phosphorus (c) Fluorine (d) Sulphur

Sodium Carbonate cannot be used in place of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}\) for the identification of \(\mathrm{Ca}^{2+}, \mathrm{Ba}^{2+}\) and \(\mathrm{Sr}^{2+}\) ions (in group V) during mixture analysis because : (a) \(\mathrm{Mg}^{2+}\) ions will also be precipitated. (b) Concentration of \(\mathrm{CO}_{3}^{2-}\) ions is very low. (c) Sodium ions will react with acid radicals. (d) \(\mathrm{Na}^{+}\)ions will interfere with the detection of \(\mathrm{Ca}^{2+}, \mathrm{Ba}^{2+}, \mathrm{Sr}^{2+}\) ions.

Which one of the following is likely to give a precipitate with \(\mathrm{AgNO}_{3}\) solution ? \(\quad\) (a) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{Cl}\) (b) \(\mathrm{CCl}_{4}\) (c) \(\mathrm{CHCl}_{3}\) (d) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}\)

Upon treatment with ammoniacal \(\mathrm{H}_{2} \mathrm{~S}\), the metal ion that precipitates as a sulfide is (a) \(\mathrm{Fe}(\mathrm{III})\) (b) Al(III) (c) \(\mathrm{Mg}(\mathrm{II})\) (d) \(\mathrm{Zn}(\mathrm{II})\)

The principle of column chromatography is : (a) Gravitational force. (b) Capillary action. (c) Differential absorption of the substances on the solid phase. (d) Differential adsorption of the substances on the solid phase.

Passing \(\mathrm{H}_{2} \mathrm{~S}\) gas into a mixture of \(\mathrm{Mn}^{2+}, \mathrm{Ni}^{2+}, \mathrm{Cu}^{2+}\) and \(\mathrm{Hg}^{2+}\) ions in an acidified aqueous solution precipitates (a) \(\mathrm{CuS}\) and \(\mathrm{HgS}\) (b) \(\mathrm{MnS}\) and \(\mathrm{CuS}\) (c) \(\mathrm{MnS}\) and \(\mathrm{NiS}\) (d) NiS and \(\mathrm{HgS}\)

A solution of a metal ion when treated with KI gives a red precipitate which dissolves in excess KI to give a colourless solution. Moreover, the solution of metal ion on treatment with a solution of cobalt (II) thiocyanate gives rise to a deep blue crystalline precipitate. The metal ion is (a) \(\mathrm{Pb}^{2+}\) (b) \(\mathrm{Hg}^{2+}\) (c) \(\mathrm{Cu}^{2+}\) (d) \(\mathrm{Co}^{2+}\)

An organic compound is estimated through Dumas method and was found to evolve 6 moles of \(\mathrm{CO}_{2}, 4\) moles of \(\mathrm{H}_{2} \mathrm{O}\) and 1 mole of nitrogen gas. The formula of the compound is: (a) \(\mathrm{C}_{12} \mathrm{H}_{8} \mathrm{~N}\) (b) \(\mathrm{C}_{12} \mathrm{H}_{8} \mathrm{~N}_{2}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{~N}_{2}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{~N}\)

A solution when diluted with \(\mathrm{H}_{2} \mathrm{O}\) and boiled, gives a white precipitate. On addition of excess \(\mathrm{NH}_{4} \mathrm{Cl} / \mathrm{NH}_{4} \mathrm{OH}\), the volume of precipitate decreases leaving behind a white gelatinous precipitate. Identify the precipitate which disolves in \(\mathrm{NH}_{4} \mathrm{OH} / \mathrm{NH}_{4} \mathrm{Cl}\) (a) \(\mathrm{Al}(\mathrm{OH})_{3}\) (b) \(\mathrm{Zn}(\mathrm{OH})_{2}\) (c) \(\mathrm{Ca}(\mathrm{OH})_{2}\) (d) \(\mathrm{Mg}(\mathrm{OH})_{2}\)

If dichloromethane (DCM) and water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) are used for differential extraction, which one of the following state-ments is correct? (a) DCM and \(\mathrm{H}_{2} \mathrm{O}\) would stay as lower and upper layer respectively in the S.F. (b) DCM and \(\mathrm{H}_{2} \mathrm{O}\) will make tur bid/colloidal mixture (c) DCM and \(\mathrm{H}_{2} \mathrm{O}\) would stay as upper and lower layer respectively in the separating funnel (S.F.) (d) \(\mathrm{DCM}\) and \(\mathrm{H}_{2} \mathrm{O}\) will be miscible clearly

A metal nitrate reacts with KI to give a black precipitate which on addition of excess of KI is converted into orange colour solution. The cation of the metal nitrate is (a) \(\mathrm{Hg}^{2+}\) (b) \(\mathrm{Bi}^{3+}\) (c) \(\mathrm{Pb}^{2+}\) (d) \(\mathrm{Cu}^{+}\)

Which of the following tests cannot be used for identifying amino acids? (a) Biuret test (b) Barfoed test (c) Ninhydrin test (d) Xanthoproteic test

A solution which is \(10^{-3} \mathrm{M}\) each in \(\mathrm{Mn}^{2+}, \mathrm{Fe}^{2+}, \mathrm{Zn}^{2+}\) and \(\mathrm{Hg}^{2+}\) is treated with \(10^{-16} \mathrm{M}\) sulphide ion. If \(K_{s p}\) of \(\mathrm{MnS}, \mathrm{FeS}, \mathrm{ZnS}\) and \(\mathrm{HgS}\) are \(10^{-15}\), \(10^{-23}, 10^{-20}\) and \(10^{-54}\) respectively, which one will precipitate first? (a) \(\mathrm{FeS}\) (b) \(\mathrm{MgS}\) (c) \(\mathrm{HgS}\) (d) \(\mathrm{ZnS}\)

\([\mathrm{X}]+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow[\mathrm{Y}]\) a colourless gas with irritating smell, \([\mathrm{Y}]+\) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow\) green solution. \([\mathrm{X}]\) and \([\mathrm{Y}]\) are: (a) \(\mathrm{SO}_{3}^{2-}, \mathrm{SO}_{2}\) (b) \(\mathrm{Cl}^{-}, \mathrm{HCl}\) (c) \(\mathrm{S}^{2-}, \mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{CO}_{3}^{2-}, \mathrm{CO}_{2}\)

For the estimation of nitrogen, \(1.4 \mathrm{~g}\) of an organic compound was digested by Kjeldahl method and the evolved ammonia was absorbed in \(60 \mathrm{~mL}\) of \(\frac{M}{10}\) sulphuric acid. The unreacted acid required \(20 \mathrm{~mL}\) of \(\frac{M}{10}\) sodium hydroxide for complete neutralization. The percentage of nitrogen in the compound is: (a) \(6 \%\) (b) \(10 \%\) (c) \(3 \%\) (d) \(5 \%\)

A gas ' \(\mathrm{X}^{\prime}\) is passed through water to form a saturated solution. The aqueous solution on treatment with silver nitrate gives a white precipitate. The saturated aqueous solution also dissolves magnesium ribbon with evolution of a colourless gas ' \(\mathrm{Y}\) '. Identify ' \(\mathrm{X}^{\prime}\) and 'Y' (a) \(\mathrm{X}=\mathrm{CO}_{2}, \mathrm{Y}=\mathrm{Cl}_{2}\) (b) \(\mathrm{X}=\mathrm{Cl}_{2}, \mathrm{Y}=\mathrm{CO}_{2}\) (c) \(\mathrm{X}=\mathrm{Cl}_{2}, \mathrm{Y}=\mathrm{H}_{2}\) (d) \(\mathrm{X}=\mathrm{H}_{2}, \mathrm{Y}=\mathrm{Cl}_{2}\)

An aqueous solution of a substance gives a white precipitate on treatment with dilute hydrochloric acid, which dissolves on heating. When hydrogen sulfide is passed through the hot acidic solution, a black precipitate is obtained. The substance is a (a) \(\mathrm{Hg}_{2}^{2+}\) salt (b) \(\mathrm{Cu}^{2+}\) salt (c) \(\mathrm{Ag}^{+}\)salt (d) \(\mathrm{Pb}^{2+}\) salt

Identify the correct order of solubility of \(\mathrm{Na}_{2} \mathrm{~S}, \mathrm{CuS}\) and \(\mathrm{ZnS}\) in aqueous medium (a) \(\mathrm{CuS}>\mathrm{ZnS}>\mathrm{Na}_{2} \mathrm{~S}\) (b) \(\mathrm{ZnS}>\mathrm{Na}_{2} \mathrm{~S}>\mathrm{CuS}\) (c) \(\mathrm{Na}_{2} \mathrm{~S}>\mathrm{CuS}>\mathrm{ZnS}\) (d) \(\mathrm{Na}_{2} \mathrm{~S}>\mathrm{ZnS}>\mathrm{CuS}\)

An aqueous solution contains \(\mathrm{Hg}^{2+}, \mathrm{Hg}_{2}^{2+}, \mathrm{Pb}^{2+}\) and \(\mathrm{Cd}^{2+} .\) The addition of \(\mathrm{HCl}(6 \mathrm{~N})\) will precipitate : (a) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\) only (b) \(\mathrm{PbCl}_{2}\) only (c) \(\mathrm{PbCl}_{2}\) and \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{PbCl}_{2}\) and \(\mathrm{HgCl}_{2}\)

The correct match between Item I and Item II is: Item I \(\quad\) Item II (A) Benzaldehyde (P) Mobile phase (B) Alumina (Q) Adsorbent (C) Acetonitrile (R) Adsorbate (a) \((\mathrm{A}) \rightarrow(\mathrm{Q}) ;(\mathrm{B}) \rightarrow(\mathrm{P}) ;(\mathrm{C}) \rightarrow(\mathrm{R})\) (b) \((\mathrm{A}) \rightarrow(\mathrm{R}) ;(\mathrm{B}) \rightarrow(\mathrm{Q}) ;(\mathrm{C}) \rightarrow(\mathrm{P})\) (c) \((\mathrm{A}) \rightarrow(\mathrm{Q}) ;(\mathrm{B}) \rightarrow(\mathrm{R}) ;(\mathrm{C}) \rightarrow(\mathrm{P})\) (d) \((\mathrm{A}) \rightarrow(\mathrm{P}) ;(\mathrm{B}) \rightarrow(\mathrm{R}) ;(\mathrm{C}) \rightarrow(\mathrm{Q})\)

Which one among the following pairs of ions cannot be separated by \(\mathrm{H}_{2} \mathrm{~S}\) in dilute hydrochloric acid? (a) \(\mathrm{Bi}^{3+}, \mathrm{Sn}^{4+}\) (b) \(\mathrm{Al}^{3+}, \mathrm{Hg}^{2+}\) (c) \(\mathrm{Zn}^{2+}, \mathrm{Cu}^{2+}\) (d) \(\mathrm{Ni}^{2+}, \mathrm{Cu}^{2+}\)

The ion that cannot be precipitated by both \(\mathrm{HCl}\) and \(\mathrm{H}_{2} \mathrm{~S}\) is (a) \(\mathrm{Pb}^{2+}\) (b) \(\mathrm{Cu}^{+}\) (c) \(\mathrm{Ag}^{+}\) (d) \(\mathrm{Sn}^{2+}\)

Among \(\mathrm{PbS}, \mathrm{CuS}, \mathrm{HgS}, \mathrm{MnS}, \mathrm{Ag}_{2} \mathrm{~S}, \mathrm{NiS}, \mathrm{CoS}, \mathrm{Bi}_{2} \mathrm{~S}_{3}\) and \(\mathrm{SnS}_{2}\), the total number of BLACK coloured sulphides is

With reference to aqua regia, choose the correct option(s) (a) Reaction of gold with aqua regia produces \(\mathrm{NO}_{2}\) in the absence of air (b) Reaction of gold with aqua regia produces an anion having Au in \(+3\) oxidation state (c) Aqua regia is prepared by mixing conc. HCl and conc. \(\mathrm{HNO}_{3}\) in \(3: 1\) \((v / v)\) ratio (d) The yellow colour of aqua regia is due to the presence of \(\mathrm{NOCl}\) and \(\mathrm{Cl}_{2}\)

The correct option(s) to distinguish nitrate salts of \(\mathrm{Mn}^{2+}\) and \(\mathrm{Cu}^{2+}\) taken separately is (are) (a) \(\mathrm{Mn}^{2+}\) shows the characteristic green colour in the flame test (b) Only \(\mathrm{Cu}^{2+}\) shows the formation of precipitate by passing \(\mathrm{H}_{2} \mathrm{~S}\) in acidic medium (c) Only \(\mathrm{Mn}^{2+}\) shows the formation of precipitate by passing \(\mathrm{H}_{2} \mathrm{~S}\) in faintly basic medium (d) \(\mathrm{Cu}^{2+} / \mathrm{Cu}\) has higher reduction potential than \(\mathrm{Mn}^{2+} / \mathrm{Mn}\) (measured under similar conditions)

The reagent(s) that can selectively precipitate \(\mathrm{S}^{2-}\) from a mixture of \(\mathrm{S}^{2-}\) and \(\mathrm{SO}_{4}^{2-}\) in aqueous solution is (are) (a) \(\mathrm{CuCl}_{2}\) (b) \(\mathrm{BaCl}_{2}\) (c) \(\mathrm{Pb}\left(\mathrm{OOCCH}_{3}\right)_{2}\) (d) \(\mathrm{Na}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]\)

The pair(s) of ions where BOTH the ions are precipitated upon passing \(\mathrm{H}_{2} \mathrm{~S}\) gas in presence of dilute \(\mathrm{HCl}\), is (are) (a) \(\mathrm{Ba}^{2+}, \mathrm{Zn}^{2+}\) (b) \(\mathrm{Bi}^{3+}, \mathrm{Fe}^{3+}\) (c) \(\mathrm{Cu}^{2+}, \mathrm{Pb}^{2+}\) (d) \(\mathrm{Hg}^{2+}, \mathrm{Bi}^{3+}\)

Which of the following statement(s) is (are) correct with reference to the ferrous and ferric ions? (a) \(\mathrm{Fe}^{3+}\) gives brown colour with potassium ferricyanide. (b) \(\mathrm{Fe}^{2+}\) gives blue precipitate with potassium ferricyanide. (c) \(\mathrm{Fe}^{3+}\) gives red colour with potassium thiocyanate. (d) \(\mathrm{Fe}^{2+}\) gives brown colour with ammonium thiocyanate.

Which of the following statement(s) is (are) correct when a mixture of \(\mathrm{NaCl}\) and \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) is gently warmed with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\) (a) A deep red vapour is evolved (b) The vapours when passed into \(\mathrm{NaOH}\) solution gives a yellow solution of \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) (c) Chlorine gas is evolved (d) Chromyl chloride is formed

Read the following statement and explanation and answer as per the options given below : Assertion : Sulphate is estimated as \(\mathrm{BaSO}_{4}\) and not as \(\mathrm{MgSO}_{4}\). Reason : Ionic radius of \(\mathrm{Mg}^{2+}\) is smaller than that of \(\mathrm{Ba}^{2+}\). (a) If both assertion and reason are correct, and reason is the correct explanation of the assertion. (b) If both assertion and reason are correct, but reason is not the correct explanation of the assertion. (c) If assertion is correct but reason is incorrect. (d) If assertion is incorrect but reason is correct.

Read the following statement and explanation and answer as per the options given below : Assertion : A very dilute acidic solution of \(\mathrm{Cd}^{2+}\) and \(\mathrm{Ni}^{2+}\) gives yellow precipitate of CdS on passing hydrogen sulphide. Statement : Solubility product of \(\mathrm{CdS}\) is more than that of NiS. (a) If both assertion and statement are correct and statement is an explanation of assertion. (b) If assertion is correct and statement is wrong, statement is not an explanation of assertion. (c) If assertion is wrong and statement is correct, statement is not an explanation of assertion. (d) If both assertion and statement are wrong and statement is not explanation of assertion.

A mixture consists of \(A\) (yellow solid) and \(B\) (colourless solid) which gives lilac colour in flame. (a) Mixture gives black precipitate \(C\) on passing \(\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})\) through its aqueous solution. (b) \(C\) is soluble in aqua-regia and on evaporation of aqua-regia and adding \(\mathrm{SnCl}_{2}\), gives greyish black precipitate \(D\). The salt solution with \(\mathrm{NH}_{4} \mathrm{OH}\) gives a brown precipitate. (i) The sodium carbonate extract of the salt withCCl \(_{4} / \mathrm{FeCl}_{3}\) gives a violet layer. (ii) The sodium carbonate extract gives yellow precipitate with \(\mathrm{AgNO}_{3}\) solution which is insoluble in \(\mathrm{NH}_{3}\). Identify \(A\) and \(B\), and the precipitates \(C\) and \(D\)

When a white crystalline compound \(\mathbf{X}\) is heated with \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\), a reddish brown gas \(\mathbf{A}\) is evolved. On passing A into caustic soda solution, a yellow coloured solution of \(\mathbf{B}\) is obtained. Neutralizing the solution \(\mathbf{B}\) with acetic acid and on subsequent addition of lead acetate, a yellow precipitate \(\mathbf{C}\) is obtained. When \(\mathbf{X}\) is heated with NaOH solution, a colourless gas is evolved and on passing this gas into \(\mathrm{K}_{2} \mathrm{HgI}_{4}\) solution, a reddish brown precipitate \(\mathbf{D}\) is formed. Identify \(\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}\) and \(\mathbf{X}\). Write the equations of reactions involved.

A white substance (A) reacts with dilute \(\mathrm{H}_{2} \mathrm{SO}_{4}\) to produce a colourless gas (B) and a colourless solution (C). The reaction between (B) and acidified \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) solution produces a green solution and a slightly coloured precipitate (D). The substance (D) burns in air to produce a gas (E) which reacts with (B) to yield (D) and a colourless liquid. Anhydrous copper sulphate is turned blue on addition of this colourless liquid. Addition of aqueous \(\mathrm{NH}_{3}\) or \(\mathrm{NaOH}\) to \((\mathrm{C})\) produces first a precipitate, which dissolves in the excess of the respective reagent to produce a clear solution in each case. Identify (A), (B), (C), (D) and (E). Write the equations of the reactions involved.

An aqueous blue coloured solution of a transition metal sulphate reacts with \(\mathrm{H}_{2} \mathrm{~S}\) in acidic medium to give a black precipitate \(\mathbf{A}\), which is insoluble in warm aqueous solution of \(\mathrm{KOH}\). The blue solution on treatment with KI in weakly acidic medium, turns yellow and produces a white precipitate \(\mathbf{B}\). Identify the transition metal ion. Write the chemical reactions involved in the formation of \(\mathbf{A}\) and \(\mathbf{B}\).

An aqueous solution containing one mole of \(\mathrm{HgI}_{2}\) and two moles of NaI is orange in colour. On addition of excess \(\mathrm{NaI}\), the solution becomes colouress. The orange colour reappears on subsequent addition of \(\mathrm{NaOCl}\). Explain with equations.

A white solid is either \(\mathrm{Na}_{2} \mathrm{O}\) or \(\mathrm{Na}_{2} \mathrm{O}_{2}\). A piece of red litmus paper turns white when it is dipped into a freshly made aqueous solution of the white solid. (i) Identify the substance and explain with balanced equation. (ii) Explain what would happen to the red litmus if the white solid were the other compound.

During the qualitative analysis of a mixture containing \(\mathrm{Cu}^{2+}\) and \(\mathrm{Zn}^{2+}\) ions, \(\mathrm{H}_{2} \mathrm{~S}\) gas is passed through an acidified solution containing these ions in order to test \(\mathrm{Cu}^{2+}\) alone. Explain briefly.