MCQs Of General Principles And Processes Of Isolation Of Elements - Past Year Questions JEE Mains, Class 12


10 Questions MCQ Test Class 12 Chemistry 35 Years JEE Mains &Advance Past yr Paper | MCQs Of General Principles And Processes Of Isolation Of Elements - Past Year Questions JEE Mains, Class 12


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QUESTION: 1

Aluminium is extracted by the electrolysis of         [2002]

Solution:

Pure aluminium can be obtained by  electrolysis of a mixture containing alumina, crayolite and fluorspar in the ratio 20 : 24 : 20. The fusion temperature of this mixture is 900ºC and it is a good conductor of electricity

QUESTION: 2

The metal extracted by leaching with a cyanide is                  [2002]

Solution:

Silver ore forms a soluble complex with NaCN from which silver is precipitated using scrap zinc.

QUESTION: 3

Which one of the following ores is best concentrated byfroth-flotation method ?       [2004]

Solution:

Froth ­flotation method is used for the concentration of sulphide ores. The method is based on the preferential wetting properties with the frothing agent and water. In the given options, Galena (PbS) is the only sulphide ore.

QUESTION: 4

During the process of electrolytic refining of copper, some metals present as impurity settle as ‘anode mud’. These are    [2005]

Solution:

During the process of electrolytic refining Ag and Au are obtained as anode mud.

QUESTION: 5

Which of the following factors is of no significance forroasting sulphide ores to the oxides and not subjecting thesulphide ores to carbon reduction directly? [2008]

Solution:

NOTE : The reduction of metal sulphides by carbon reduction process is not spontaneous because DG for such a process is positive. The reduction of metal oxide
by carbon reduction process is spontaneous as DG for such a process is negative.
From this we find that on thermodynamic considerations CO2 is more stable than CS2 and the metal sulphides are more stable than corresponding oxides.
In view of above the factor listed in choice (c) is incorrect and so is of no significance.
Hence the correct answer is (c)

QUESTION: 6

29.5 mg of an organic compound containing nitrogen wasdigested according to Kjeldahl’s method and the evolvedammonia was absorbed in 20 mL of 0.1 M HCl solution. Theexcess of the acid required 15 mL of 0.1 M NaOH solutionfor complete neutralization. The percentage of nitrogen inthe compound is                [2010]

Solution:

Moles of HCl taken = 20 × 0.1 × 10–3 =  2 × 10–3
Moles of HCl neutralised by NaOH solution
= 15 × 0.1 × 10–3 = 1.5 × 10–3
Moles of HCl neutralised by ammonia
= 2 × 10–3 – 1.5 × 10–3
= 0.5 × 10–3

QUESTION: 7

Which method of purification is represented by the following equation ? [2012]

Solution:

Van Arkel is a method in which heat treatment is used to purify metal in this process metals are converted into other metal compound for loosly coupled like as iodine to make metal iodide which are easily decomposed and give pure metal.
The process is known as Van Arkel method.

QUESTION: 8

The metal that cannot be obtained by electrolysis of anaqueous solution of its salts is: [JEE M 2014]

Solution:

On electrolysis of aqueous solution of s-block elements H2 gas discharge at cathode.

QUESTION: 9

In the context of the Hall - Heroult process for the extraction of Al, which of the following statements is false ?[JEE M 2015]

Solution:

(a) In Hall-Herouit process for extraction of Al, carbon anode is oxidised to CO and CO2  
(b) When Al is mixed with CaF2, it lowers the melting point of the mixture brings conductivity.
(c) Al3+ is reduced at cathode to form Al.
(d) Here, Al2O3 is an electrolyte, undergoing the redox process. Na3AlF6 although is an electrolyte but serves as a solvent, not electrolyte

QUESTION: 10

Which one of the following ores is best concentrated byfroth floatation method? [JEE M 2016]

Solution:

Froth floatation method is mainly applicable for
sulphide ores.
(1) Malachite ore : Cu(OH)2 . CuCO3
(2) Magnetite ore : Fe3O4
(3) Siderite ore : FeCO3
(4) Galena ore : PbS (Sulphide Ore)