Explain:
(i)Zone refining
(ii)Column chromatography.
(i) Zone refining: This method is used for production of semiconductors and other metals of very high purity, e.g., Ge, Si, B, Ca and In.
It is based on the principle that the impurities
are more soluble in the molten state (melt) than in the solid state of the metal.
The impure metal in the form of bar is heated at one end with a moving circular heater. As – the heater is slowly moved along the length of the rod, .the pure metal crystallises out of the melt whereas the impurities pass into the adjacent molten zone. Thi,s process is repeated several times till the impurities are completely driven to one end of the rod which is then cut off and discarded.
(ii) Chromatography: It is based on the principle that the different components of a mixture are adsorbed to different extents on an adsorbent.
In column chromatography, an adsorbent, such as alumina (Al2O3) or silica gel is packed in a column. This fonns the stationary phase. The mixture to be separated is dissolved in a suitable solvent (mobile phase) and applied to the top of the column. The adsorbed components are extracted (eluted) from the column with a suitable . solvent (eluent). The component which is more strongly adsorbed on the column takes longer time to travel through the column than a component which is weakly adsorbed. Thus, the various components of the mixture are seperated as they travel through absorbent (stationary phase).
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?
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.
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?
Assertion (A): Zirconium can be purified by van Arkel method.
Reason (R): ZrI4 is volatile and decomposes at 1800 K.
Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?
Write down the reactions taking place in blast furnace related to the metallurgy of iron at the temperature range 500-800 K.
Which of the following ores are concentrated by froth floatation?
(a) Haematite (b) Galena
(c) Copper pyrites (d) Magnetite
Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.
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.
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.
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.
Assertion (A): Zone refining method is very useful for producing semiconductors.
Reason (R): Semiconductors are of high purity.
Assertion (A): Sulphide ores are concentrated by froth floatation method. Reason (R): Cresols stabilize the froth in froth floatation method.
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
What criterion is followed for the selection of the stationary phase in chromatography?
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.
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.
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
Why is an external emf of the more than 2.2 V required for the extraction of Cl2 from brine?
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?
At temperatures above 1073 K coke can be used to reduce FeO to Fe. How can you justify this reduction with Ellingham diagram?
Explain the following:
(a)CO2 is a better reducing agent below 710 K whereas CO is a better reducing agent above 710 K.
(b) Generally sulphide ores are converted into oxides before reduction.
(c) Silica is added to the sulphide ore of copper in the reverberatory furnac
(d) Carbon and hydrogen are not used as reducing agents at high temperatures.
(e) Vapour phase refining method is used for the purification of Ti.
Is it true that under certain conditions, Mg can reduce Al203 and Al can reduce MgO? What are those conditions?
Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?