Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

In extractive metallurgy of zinc partial fusion of ZnO with coke is called ______ and reduction of the ore to the molten metal is called________ .

  1. sintering, smelting

  2. roasting, smelting

  3. sintering, roasting

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sintering is the process of forming a solid mass of material by heat and/or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a manufacturing process used with metals, ceramics, plastics, and other materials.

Smeltings main use is to produce a metal from its ore. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gasses or slag and leaving just the metal behind. The reducing agent is commonly a source of carbon.The carbon removes oxygen from the ore, leaving behind elemental metal. 

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Carbon reduction method is employed for commercial extraction of :

  1. haematite

  2. cassiterite

  3. iron pyrite

  4. corundum
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

In extraction of tin from cassiterite-
$SnO _2+2C\rightarrow Sn+2CO$

In extraction of iron from haematite -
$Fe _2O _3+3CO\rightarrow 2Fe+3CO _2$

Iron pyrite $FeS _2$ is a sulphide ore for which froth floatation method is used.
Corundum is a crystalline form of aluminium oxide $Al _2O _3$ with traces of iron, titanium and chromium; for which electrolytic reduction method is used.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Highly electropositive metals cannot be extracted by carbon reduction process because, these:

  1. metals combine with carbon to form carbides

  2. metals do not react with carbon

  3. metal oxides are not reduced by carbon

  4. loss of metal is more in vaporisation
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

Highly electropositive metals cannot be extracted by carbon reduction process because of two reasons
(i) Metals combine with carbon to form carbides.
(ii) Loss of metal is more in vaporization.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Of the following reduction processes, correct processes are :

  1. $Fe _{2}O _{3}$ + $C$ $\rightarrow$ $Fe$
  2. $ZnO$ + $C$ $\rightarrow$ $Zn$
  3. $Ca _{3}(PO _{4}) _{2}$ + $C$ $\rightarrow$ $P$
  4. $PbO$ + $C$ $\rightarrow$ $Pb$
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

(A) Carbon reduces ferric oxide to iron. $Fe _2O _3+3C \rightarrow 2Fe + 3CO$.
Thus option A is correct.
(B) Carbon reduces zinc oxide to zinc. $ZnO+C \rightarrow {\triangle} {1673  K} Zn + CO \uparrow$.
Thus option B is correct.
(C) In presence of silica, carbon reduces calcium phosphate to free phosphorus.
$2 Ca _3(PO _4) _2 + 9 SiO _2 + 16 C  \rightarrow 6 CaSiO _3 + P _4 + 16 CO$
Thus option C is correct.
(D) Carbon reduces lead oxide to lead. $2PbO+C \rightarrow 2Pb+CO _2$.
Thus option D is correct.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

The disadvantage of carbon reduction method are :

  1. high temperature needed which is expensive and requires the use of a blast furnace

  2. many metals combine with carbon forming carbides
  3. carbon combines with oxygen to form poisonous $CO$

  4. carbon cannot be used with highly electropositive metals
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

 The disadvantage of carbon reduction method are
(i) high temperature needed which is expensive and requires the use of a blast furnace
(ii) many metals combine with carbon forming carbides
(iii) carbon dioxide gas is released in the process which is green house gas.
(iii) metals produced contain significant amount of carbon. hence, metals obtained cannot be very pure.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Pyrometallurgical method used for the extraction of copper from sulphide ore:

  1. is a dry method
  2. involves concentration by leaching the sulphide ore with dil. $H _2SO _4$

  3. involves concentration of the sulphide ore by froth flotation process

  4. statement given in (b) is incorrect
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The copper is extracted from sulphide ore by pyrometallurgy which involves reduction of the concentrated ore at high temperature.
This process is a dry process.
In this process, the sulphide ore is concentrated by froth floatation process.
In this process, the sulphide ore is not concentrated by leaching with dil sulphuric acid.
Thus, the statement B is incorrect and the statement A and C are correct.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Write chemical equations for metallurgical processes to represent the reduction of $Cu _2O$ using charcoal as a reducing agent :

  1. $2Cu _2O\, +\, C\, \overset{\Delta}{\rightarrow}\, 4Cu\, +\, CO _2$
  2. $Cu _2O\, +\, C\, \overset{\Delta}{\rightarrow}\, 2Cu\, +\, CO$
  3. $3Cu _2O\, +\, 2C\, \overset{\Delta}{\rightarrow}\, 6Cu\, +\, CO +\, CO _2$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Chemical equations for reduction of $Cu _2O$ using charcoal as a reducing agent : 

$Cu _2O\, +\, C\, \overset{\Delta}{\rightarrow}\, 2Cu\, +\, CO$.

This process is carbon reduction.


Hence option B is correct.