Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.
Gold particles present in the ore are treated with a dilute solution of NaCN and air is circulated. Gold particles dissolve by forming soluble complex.
Au is recovered from solution by the addition of electropositive metal like zinc.
Extraction of gold by cyanide process involves both oxidation and reduction. Formation of cyanide complex involves oxidation of gold while its recovery involves reduction. Zn acts as a reducing agent.
Extraction of gold and silver involves leaching the metal with CN+ ion. The metal is recovered by
(a) displacement of metal by some other metal from the complex ion
(b) roasting of metal complex
(c) calcinations followed by roasting
(d) thermal decomposition of metal complex
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?
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.
The main reactions occurring in blast furnace during extraction of iron from haematite are
Assertion (A): Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.
Reason (R): Copper is extracted by hydrometallurgy.
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.
Assertion (A): Zirconium can be purified by van Arkel method.
Reason (R): ZrI4 is volatile and decomposes at 1800 K.
Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?
Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.
The value of ΔfG ° for formation of Cr2O3 is – 540 kJ mol-1 and that of Al203 is – 827 kJ mol-1 . Is the reduction of Cr2O3 possible with Al?
In the froth floatation process, zinc sulphide and lead sulphide can be separated by
(a) using collectors
(b) adjusting the proportion of oil to water
(c) using depressant
(d) using froth stabilisers
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.
Assertion (A): Sulphide ores are concentrated by froth floatation method. Reason (R): Cresols stabilize the froth in froth floatation method.
Which of the following statements are correct about the role of substances added in the froth floatation process?
(a) Collectors enhance the non-wettability of the mineral particles.
(b) Collectors enhance the wettability of gangue particles.
(c) By using depressants in the process two sulphide ores can be separated.
(d) Froth stabilizers decrease wettability of gangue.
Assertion (A): Zone refining method is very useful for producing semiconductors.
Reason (R): Semiconductors are of high purity.
Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?
Why is an external emf of the more than 2.2 V required for the extraction of Cl2 from brine?
The purest form of iron is prepared by oxidizing impurities from cast iron in a reverberatory furnace. Which iron ore is used to line the furnace? Explain by giving reaction.
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
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.
Outline the principles of refining of metals by the following methods:
(i) Zone refining
(ii) Electrolytic refining
(iii) Vapour phase refining
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.
What criterion is followed for the selection of the stationary phase in chromatography?
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.
Is it true that under certain conditions, Mg can reduce Al203 and Al can reduce MgO? What are those conditions?
