d and f Block Elements — Page 2 | JEE Chemistry

Q11

Given below are two statements : Statement I : In froth floatation method of rotating paddle agitates the mixture to drive air out of it. Statement II : Iron pyrites and generally avoided for extraction of iron due to environmental reasons. In the light of the above statements, choose the correct answer from the options given below :

A Statement I is true but Statement II is false

B Statement I is false but Statement II is true

C Both Statement I and Statement II are true

D Both Statement I and Statement II are false

Correct Answer

Option B

Solution

Statement I is false because the rotating paddle in froth floatation method agitates the mixture to generate froth and not to drive air out of it.

Statement II is true because iron is commercially extracted from haematite ore and not from iron pyrites to minimize environmental pollution.

Q12

The metal ion (in gaseous state) with lowest spin-only magnetic moment value is :

A V2+

B Ni2+

C Cr2+

D Fe2+

Correct Answer

Option B

Solution

Valence shell configuration Unpaired electrons V2+ 3d34s0 n = 3 Ni2+ 3d84s0 n = 2 Cr2+ 3d44s0 n = 4 Fe2+ 3d64s0 n = 4 Since Ni2+ has least number of unpaired electrons.

Hence Ni2+ will have lowest spin only magnetic moment Value.

Q13

The correct set of ions (aqueous solution) with same colour from the following is:

A

\mathrm{V}^{2+}, \mathrm{Cr}^{3+}, \mathrm{Mn}^{3+}

B

\mathrm{Ti}^{4+}, \mathrm{V}^{4+}, \mathrm{Mn}^{2+}

C

\mathrm{Sc}^{3+}, \mathrm{Ti}^{3+}, \mathrm{Cr}^{2+}

D

\mathrm{Zn}^{2+}, \mathrm{V}^{3+}, \mathrm{Fe}^{3+}

Correct Answer

Option A

Solution

(1) $\mathrm{V}^{2+}$ (Violet), $\mathrm{Cr}^{3+}$ (Violet), $\mathrm{Mn}^{3+}$ (Violet) (2) $\mathrm{Zn}^{2+}$ (Colourless), $\mathrm{V}^{3+}$ (Green), $\mathrm{Fe}^{3+}$ (Yellow) (3) $\mathrm{Ti}^{4+}$ (Colourless), $\mathrm{V}^{4+}$ (Blue), $\mathrm{Mn}^{2+}$ (Pink) (4) $\mathrm{Sc}^{3+}$ (Colourless), $\mathrm{Ti}^{3+}$ (Purple), $\mathrm{Cr}^{2+}$ (Blue)

Q14

Statement I : Leaching of gold with cyanide ion in absence of air / O2 leads to cyano complex of Au(III). Statement II : Zinc is oxidized during the displacement reaction carried out for gold extraction. In the light of the above statements, choose the correct answer from the options given below.

A Both Statement I and Statement II are correct.

B Both Statement I and Statement II are incorrect.

C Statement I is correct but Statement II is incorrect.

D Statement I is incorrect but Statement II is correct.

Correct Answer

Option D

Solution

Leaching of gold with cyanide ion is done in presence of air/O2 leading to cyano complex [Au(CN)2]– where Au is in +1 oxidation state.

4Au(s) + 8CN–(aq) + 2H2O(aq) + O2(g)

\longrightarrow 4\left[\mathrm{Au}(\mathrm{CN})_{2}\right]_{\mathrm{aq}}^{-}+4 \mathrm{OH}^{-}

\begin{aligned} 2\left[\mathrm{Au}(\mathrm{CN})_{2}\right]_{(\mathrm{aq})}^{-} &+\mathrm{Zn}(\mathrm{s}) \\ & \longrightarrow\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]_{(\mathrm{aq})}^{2-}+2 \mathrm{Au}(\mathrm{s}) \end{aligned}

Zinc is oxidised from (0) to +2 oxidation state during displacement reaction carried out for gold extraction.

Q15

The correct statement is :

A leaching of bauxite using concentrated NaOH solution gives sodium aluminate and sodium silicate

B the Hall-Heroult process is used for the production of aluminium and iron

C pig iron is obtained from cast iron

D the blistered appearance of copper during the metallurgical process is due to the evolution of CO2

Correct Answer

Option A

Solution

(A) Leaching of bauxite : Al2O3.

H2O + NaOH $\to$ Na[Al(OH)4] + Na2SiO3 So, option (A) is correct.

(B) Hall Heroult’s process is used for aluminium only not for iron.

So, option (B) is wrong.

(C) From Blast Furnace, at the end we get pig iron and in pig iron percentage of carbon is high and after reducing the carbon percantage we get cast iron.

So we can say cast iron is obtained from pig iron.

So, option (C) is wrong.

(D) In Bessemer converter following reaction happens : Cu2S + Air $\to$ Cu2O + SO2 Cu2O + Cu2S $\to$ Cu + SO2 So we can say, Appearance of Blister copper is due to evolution of SO2 gas.

$\therefore$ Option (D) is wrong.

Q16

How do we differentiate between Fe3+ and Cr3+ in group III?

A by taking excess of NH4OH solution

B by increasing

NH_4^+

ion concentration

C by decreasing OH- ion concentration

D both (b) and (c)

Correct Answer

Option B

Solution

FeCl3 + 3NH4OH $\to$ Fe(OH)3 ↓(reddish brown) + 3NH4Cl CrCl3 + 3NH4OH $\to$ Cr(OH)3 (Bluish green) + 3NH4Cl

Q17

The setting time of Cement is increased by adding :

A Gypsum

B Limestone

C Clay

D Silica

Correct Answer

Option A

Solution

The setting time of cement is increased by adding gypsum.

Q18

Which element is not present in Nessler's reagent?

A Mercury

B Iodine

C Potassium

D Oxygen

Correct Answer

Option D

Solution

Nessler’s reagent is K2[HgI4] Therefore, among the options given, oxygen is the only element that is not present in Nessler's reagent.

Q19

Which one amongst the following are good oxidizing agents? A. Sm

^{2+}

B. Ce

^{2+}

C. Ce

^{4+}

D. Tb

^{4+}

Choose the most appropriate answer from the options given below :

A C and D only

B A and B only

C D only

D C only

Correct Answer

Option A

Solution

The most appropriate answer is $C$ and $D$ only. $Ce^{4+}$ and $Tb^{4+}$ are good oxidizing agents because they have a high oxidation state and a strong tendency to gain electrons. $Sm^{2+}$ and $Ce^{2+}$ are reducing agents because they have a low oxidation state and a tendency to lose electrons.

Q20

The metals that are employed in the battery industries are A.

\mathrm{Fe}

B.

\mathrm{Mn}

C.

\mathrm{Ni}

D.

\mathrm{Cr}

E.

\mathrm{Cd}

Choose the correct answer from the options given below:

A A, B, C, D and E

B A, B, C and D only

C B, D and E only

D B, C and E only

Correct Answer

Option D

Solution

Mn, Ni and Cd metals used in battery industries.