JEE Chemistry Salt Analysis MCQs Set 02

Answer: (d) CdS and As2S3

Explanation:
1. As2S3 (arsenic subgroup) dissolves in yellow ammonium sulphide forming thioarsenate, while CdS does not.
2. The other pairs both stay insoluble.

Teacher's Note:
1. Group IIB sulphides dissolve in yellow (NH4)2Sx.
2. Group IIA sulphides do not.

Answer: (d) \( \ce{CuCO3} \)

Explanation:
1. CuCO3 dissolves in HCl as soluble CuCl2.
2. Ag2CO3 forms AgCl and Hg2CO3 forms Hg2Cl2, both precipitates.

Teacher's Note:
1. Group I chlorides precipitate in HCl.
2. Copper chloride is soluble.

Answer: (d) Lead

Explanation:
1. PbCrO4 is yellow and dissolves in NaOH as plumbite and chromate.
2. Silver chromate is brick red.

Teacher's Note:
1. Lead chromate dissolves in alkali and in nitric acid.
2. It does not dissolve in acetic acid.

Answer: (a) \( \ce{Hg2Cl2} \)

Explanation:
1. Sn2+ reduces Hg2+ to Hg2Cl2, which is white and silky.
2. Excess SnCl2 reduces it further to grey mercury.

Teacher's Note:
1. Calomel is Hg2Cl2.
2. Small amount gives white, excess gives grey.

Answer: (c) Ammonia solution

Explanation:
1. Ammonia gives white HgO.Hg(NH2)NO3 from Hg(NO3)2.
2. Co(SCN)2 gives blue, excess SnCl2 gives grey mercury and KCN gives soluble Hg(CN)2.

Teacher's Note:
1. Mercuric amido compounds are white.
2. Mercurous gives black with ammonia.

Answer: (a) Cupric chloride

Explanation:
1. CuS is black.
2. CdS is yellow, ZnS is white and ferric chloride is reduced with deposition of sulphur.

Teacher's Note:
1. Colours of sulphides help identification.
2. Black: CuS, PbS, HgS, Bi2S3.

Answer: (b) (A), (C), (D)

Explanation:
1. Iodide reduces Cu2+ to CuI, thiocyanate gives CuSCN and cyanide gives CuCN (via unstable Cu(CN)2).
2. Chloride does not reduce Cu2+.

Teacher's Note:
1. I-, SCN- and CN- are reducing ligands for Cu(II).
2. KCl gives no redox change.

Answer: (c) \( \ce{BiOCl} \)

Explanation:
1. BiCl3 is hydrolysed to bismuth oxychloride BiOCl, a white precipitate.
2. It dissolves again on adding HCl.

Teacher's Note:
1. BiCl3 + H2O gives BiOCl + 2HCl.
2. Same is seen with SbCl3.

Answer: (d) The concentration of OH- decreases

Explanation:
1. NH4Cl supplies NH4+, a common ion that suppresses ionisation of NH4OH.
2. So [OH-] falls.

Teacher's Note:
1. Common ion effect.
2. Used to avoid precipitating group IV hydroxides.

Answer: (b) \( \ce{Fe^{3+}} \)

Explanation:
1. Fe3+ gives a brown colouration with K3[Fe(CN)6] and a reddish-brown ferric acetate colour with sodium acetate.
2. Ni2+ and Cu2+ do not give these.

Teacher's Note:
1. Fe3+: reddish-brown with acetate, blood red with SCN-.
2. Fe2+: Turnbull's blue with ferricyanide.

Answer: (b) Ferrous ferricyanide

Explanation:
1. Turnbull's blue is Fe3[Fe(CN)6]2, ferrous ferricyanide.
2. Prussian blue is ferric ferrocyanide.

Teacher's Note:
1. Fe2+ with ferricyanide gives Turnbull's blue.
2. Fe3+ with ferrocyanide gives Prussian blue.

Answer: (c) NaOH/H2O2

Explanation:
1. NaOH with H2O2 converts Cr(OH)3 into soluble yellow chromate and leaves Fe(OH)3 undissolved.
2. Aq. NH3 precipitates both and acids dissolve both.

Teacher's Note:
1. Cr3+ is oxidised to CrO4(2-).
2. Fe(OH)3 is not amphoteric.

Answer: (d) All

Explanation:
1. Fe3+ gives a blood red colour, Co2+ a blue complex in acetone and Cu2+ a black precipitate Cu(SCN)2.
2. So thiocyanate tests all three.

Teacher's Note:
1. Different complexes, different colours.
2. Cu(SCN)2 turns white CuSCN with SO2.

Answer: (d) All of these

Explanation:
1. Ferrocyanide gives white (Fe2+), Prussian blue (Fe3+), white (Zn2+), brown (Cu2+), white (Ag+) and white mixed salt with Ca2+ in ammonium chloride.
2. So all can be detected.

Teacher's Note:
1. Ca2+ test needs NH4Cl and NH3.
2. Know the colours.

Answer: (b) HCl (aq)

Explanation:
1. HCl protonates NH3 to NH4+, removing free NH3 and shifting the equilibrium towards free Zn2+.
2. NH3 would do the opposite.

Teacher's Note:
1. Le Chatelier's principle.
2. Acid destroys ammonia complexes.

Answer: (a) Ni

Explanation:
1. Nickel forms the rose red, insoluble bis(dimethylglyoximato)nickel(II).
2. Zn, Co and Mn do not give this.

Teacher's Note:
1. Brunner's test for nickel.
2. Fe2+ gives a red solution only.

Answer: (d) Zn

Explanation:
1. Zn(OH)2 dissolves in excess NH3 as [Zn(NH3)4]2+, and H2S then gives white ZnS.
2. Al(OH)3 does not dissolve in excess ammonia.

Teacher's Note:
1. Only Zn gives white ZnS.
2. Ca and Ba do not form hydroxide precipitates with ammonia.

Answer: (b) Metaborate

Explanation:
1. Borax on heating gives sodium metaborate and B2O3, which combine with metal oxides to form coloured metaborates.
2. For example CuO + B2O3 gives Cu(BO2)2.

Teacher's Note:
1. Borax bead contains metaborates.
2. Colour depends on the metal and flame.

Answer: (a) (A), (B), (C), (D)

Explanation:
1. Zn(OH)2 is amphoteric and dissolves in NaOH as zincate and in acids.
2. It also forms [Zn(NH3)4]2+ with ammonia and dissolves in ammonium salts.

Teacher's Note:
1. Zn(OH)2 is amphoteric and forms an ammine.
2. Ammonium salts lower [OH-].

Answer: (c) Na2SO4(aq)

Explanation:
1. Ba, Ca and Pb carbonates are insoluble.
2. Na2SO4 gives only soluble sodium and potassium salts.

Teacher's Note:
1. Alkali metal carbonates are soluble.
2. Group V metals give carbonates.

Answer: (c) \( \ce{BaCl2} \)

Explanation:
1. BaCl2 gives white AgCl with silver nitrate and white BaSO4 with dilute sulphuric acid.
2. Pb(NO3)2 gives no chloride, and nitrates give no AgNO3 precipitate.

Teacher's Note:
1. Need both Cl- and a sulphate-insoluble cation.
2. CuCl2 gives no sulphate precipitate.

Answer: (b) Strontium

Explanation:
1. Strontium compounds impart a crimson red flame.
2. K gives lilac, Ba apple green and Ca brick red.

Teacher's Note:
1. Flame colours help in identification.
2. Ca is brick red.

Answer: (d) All of these

Explanation:
1. Titan yellow gives a red colour (lake), Na2HPO4 gives white MgNH4PO4 and magneson I gives a blue lake.
2. All three are valid tests.

Teacher's Note:
1. Several tests exist for Mg2+.
2. All need alkaline medium.

Answer: (c) (B), (C)

Explanation:
1. Sulphate gives white PbSO4 and BaSO4, and hydrogen phosphate gives white phosphates of both.
2. Chloride gives a precipitate with Pb only and chromate gives yellow precipitates.

Teacher's Note:
1. Check colour and which cation.
2. BaCl2 is soluble.