Chemistry

Isolation of Elements

Question:

Brine is electrolysed by using inert electrodes. The reaction at anode is
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-7

Answer:

(a) For oxidation at anode, two possible reactions are oxidation of chlorine and of oxygen. Out of these two, oxidation of chlorine ion is preferred because oxidation of oxygen requires overvoltage.
Chlorine is obtained by electrolysis giving out hydrogen and aqueous NaOH as byproducts.

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Isolation of Elements

Q 1.

Match the items of Column I with items of Column II and assign the correct code:
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-36

Q 2.

The mixture of compounds A and B is passed through a column of Al2O3 by using alcohol as eluent. Compound A is eluted in preference to compound B. Which of the compounds A or B is more readily adsorbed on the column?

Q 3.

What is meant by the term "chromatography"?

Q 4.

In the metallurgy of aluminium
(a) Al3+ is oxidized to Al(s)
(b) graphite anode is oxidized to carbon monoxide and carbon dioxide
(c) oxidation state of oxygen changes in the reaction at anode
(d) oxidation state of oxygen changes in the overall reaction involved in the process.

Q 5.

I low is cast iron' different from pig iron '?

Q 6.

What is the role of cryolite in the metallurgy of aluminium?

Q 7.

For the metallurgical process of which of the ores, calcined ore can be reduced by carbon?
(a) Haematite (b) Calamine (c) Iron pyrites (d) Sphalerite

Q 8.

t the temperature corresponding to which of the points in figure of Q. 11-13, FeO will be reduced to Fe by coupling the reaction 2FeO —> 2Fe + 02 with all of the following reactions?
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-15

Q 9.

Assertion (A): Zirconium can be purified by van Arkel method.
Reason (R): ZrI4 is volatile and decomposes at 1800 K.

Q 10.

Which of the following reaction is an example of autoreduction?
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-3
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-4

Q 11.

Which of the ores mentioned  can be concentrated by magnetic separation method?

Q 12.

Match the items of Column I with the items of Column II and assign the correct code:
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-37

Q 13.

Write down the reactions taking place in blast furnace related to the metallurgy of iron at the temperature range 500-800 K.

Q 14.

Predict conditions under which Al might be expected to reduce MgO.

Q 15.

In the extraction of aluminium by Hall-Heroult process, purified A1203 is mixed with CaF2 to
(a) lower the melting point of A1203.
(b) increase the conductivity of molten mixture.
(c) reduce Al+3 into Al(s).
(d) acts as catalyst.

Q 16.

What is the role of depressant in froth-floatation process?

Q 17.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices.
(a) Both Assertion and Reason are true and the Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true and the Reason is not the correct explanation of Assertion.
(c) Assertion is true but the Reason is false.
(d) Assertion is false but Reason is true.
(e) Assertion and Reason both are wrong.

Assertion (A): Nickel can be purified by Mond's process.
Reason (R): Ni(CO)4 is a volatile compound which decomposes at 460 K to give pure Ni.

Q 18.

ncert-solutions-for-class-12-chemistry-general-principles-and-processes-of-isolation-of-elements-3

Q 19.

Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?

Q 20.

The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.

Q 21.

Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

Q 22.

Which of the following ores are concentrated by froth floatation?
(a) Haematite (b) Galena
(c) Copper pyrites (d) Magnetite

Q 23.

Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

Q 24.

Which of the following options are correct?
(a) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.
(b) In extraction of silver, silver is extracted as cationic complex.
(c) Nickel is purified by zone refining.
(d) Zr and Ti are purified by van Arkel method.

Q 25.

What should be the considerations during the extraction of metals by electrochemical method?

Q 26.

Assertion (A): Zone refining method is very useful for producing semiconductors.
Reason (R): Semiconductors are of high purity.

Q 27.

Write chemical reactions taking place in the extraction of zinc from zinc blende.

Q 28.

What criterion is followed for the selection of the stationary phase in chromatography?

Q 29.

Name the processes from which chlorine is obtained as a by-product What will happen if an aqueous solution of NaCl is subjected to electrolysis?

Q 30.

In the extraction of chlorine from brine .
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-22

Q 31.

At temperatures above 1073 K coke can be used to reduce FeO to Fe. How can you justify this reduction with Ellingham diagram?

Q 32.

Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?

Q 33.

Match the items of Column I with the items of Column II and assign the correct code:
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-38

Q 34.

Is it true that under certain conditions, Mg can reduce Al203 and Al can reduce MgO? What are those conditions?

Q 35.

What is the role of graphite rod in the electrometallurgy of aluminium?

Q 36.

Choose the correct option of temperature at which carbon reduces FeO to iron and produces CO.
(a) Below temperature at point A
(b) Approximately at the temperature corresponding to point A
(c) Above temperature at point A but below temperature at point D
(d) Above temperature at point A

Q 37.

In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?
(a) Heating with stream of carbon monoxide
(b) Heating with iodine
(c) Liquation
(d) Distillation

Q 38.

Which of the following statements are correct?
(a) A depressant prevents certain type of particle to come to the froth.
(b) Copper matte contains Cu2S and ZnS.
(c) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.
(d) Zinc can be extracted by self-reduction.

Q 39.

Copper can be extracted by hydrometallurgy but not zinc. Explain.

Q 40.

State the role of silica in the metallurgy of copper.

Q 41.

Describe a method for refining nickel.

Q 42.

Differentiate between "minerals"and "ores'.

Q 43.

Out of C and CO, which is a better reducing agent for ZnO?

Q 44.

Brine is electrolysed by using inert electrodes. The reaction at anode is
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-7

Q 45.

The main reactions occurring in blast furnace during extraction of iron from haematite are
ncert-exemplar-problems-class-12-chemistry-general-principles-processes-isolation-elements-19

Q 46.

Write two basic requirements for refining of a metal by Mond's process and by van Arkel method.Why?

Q 47.

Why is sulphide ore of copper heated in a furnace after mixing with silica? Iron oxide present as impurity in sulphide ore of copper forms a slag of iron silicate and copper is produced in the form of copper matte.

Q 48.

Give two requirements for vapour phase refining.

Q 49.

Explain:
(i)Zone refining
(ii)Column chromatography.

Q 50.

How is leaching carried out in case of low grade copper ores?