Tag: chemistry

Questions Related to chemistry

When hypohalites are heated at $300K$, the product obtained are:

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. halide

  2. halogen

  3. perhalate

  4. halate

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Correct Option: A,D
Explanation:

Hypohalites $(XO^-)$ disproportionates in aqueous solution on heating to produce halide ion and halate ion.


$\underset {(Hypohalite)}{3XO^-}\overset {300K}{\rightleftharpoons}\underset {(Halide)}{{2X}^-}+\underset {(Halate)}{{XO _3}^-}$

Iodine solution is prepared by dissolving iodine in

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $NaOH$

  2. $Na _{2}CO _{3}$

  3. $H _{2}O$

  4. $KI$

Show answer
Correct Option: D
Explanation:

Iodine solutions are prepared by dissolving $I _2$ in a concentrated solution of potassium iodide ($KI$).
Hence option D is correct.

The colour of the ${X} _{2}$ molecules of group $17$ elements changes gradually from yellow to violet down the group. This is due to:

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. the physical state of ${X} _{2}$ at room temperature changes from gas to solid down the group

  2. decrease in ${\pi}^{\ast} - {\sigma}^{\ast}$ gap down the group

  3. decrease in $HOMO-LUMO$ gap down the group

  4. decrease in ionization energy down the group

Show answer
Correct Option: B,C
Explanation:

The colour of the $\displaystyle X _2$ molecules of group 17 elements changes gradually from yellow to violet down the group. This is due to  (B) Decrease in $\displaystyle {\pi}^{\ast} - {\sigma}^{\ast}$ gap down the group and (C) decrease in HOMO−LUMO gap down the group. Halogens absorb visible light and appear coloured. Outer electrons are excited to higher energy level. Smaller halogen has higher excitation energy and vice versa.

Reduction potentials of some ions are given below. Arrange them in decreasing order of oxidizing power.

Ion $Cl{ O } _{4}^{-}$ $I{ O } _{4}^{-}$ $Br{ O } _{4}^{-}$
Reduction potential $E^{\circ}$/V $E^{\circ}$= 1.19V $E^{\circ}$= 1.65V $E^{\circ}$= 1.74V
group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $Cl{ O } _{4}^{-}$ > $I{ O } _{4}^{-}$ > $Br{ O } _{4}^{-}$

  2. $I{ O } _{4}^{-}$ > $Br{ O } _{4}^{-}$ > $Cl{ O } _{4}^{-}$

  3. $Br{ O } _{4}^{-}$ > $I{ O } _{4}^{-}$ > $Cl{ O } _{4}^{-}$

  4. $Br{ O } _{4}^{-}$ > $Cl{ O } _{4}^{-}$ > $I{ O } _{4}^{-}$

Show answer
Correct Option: C
Explanation:

The reduction potential of the substance is the ability of the substance to be reduced.So as the reduction potential increases reducing ability of the  substance increases.It means oxidizing power of the substance (The ability of the substance to make the other substance to lose the electrons increases which noting but oxidizing power) increases.

So the decreasing order of oxidizing power is $Br{ O } _{4}^{-}$ > $I{ O } _{4}^{-}$ > $Cl{ O } _{4}^{-}$.

Hence option $C$ is correct.

Which of the following sulphides when  heated strongly in air gives the corresponding metal without undergoing separate reduction of oxide?

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. $Cu _2S$

  2. $FeS$

  3. $HgS$

  4. $ZnS$

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Correct Option: B
Explanation:

$2Cu _2S+3O _2\longrightarrow 2Cu _2O+2SO _2$

$2ZnS+3O _2\longrightarrow 2ZnO+2SO _2$
$2PbS+3O _2\longrightarrow 2PbO+2SO _2$
$2HgS+3O _2\longrightarrow 2HgO+2SO _2$
$FeS+O _2\longrightarrow Fe+SO _2$
$FeS$ when heated directly in air gives $Fe$. 

Which of the following reactions show the process of smelting?

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. $2PbO + PbS \rightarrow 3Pb + SO _2$

  2. $2Na[Au(CN) _2]+Zn \rightarrow Na _2[Zn(CN) _4]+2Au$

  3. $PbO+C\rightarrow Pb + CO$

  4. $2HgS + 3O _2\rightarrow 2HgO+2SO _2$

Show answer
Correct Option: C
Explanation:

Carbon reduction occurs in smelting from oxide ore. $PbO+C\longrightarrow Pb+CO$

Fill in the blanks with the correct choice.
The undesired impurities present in the ores are called (i). To remove the volatile impurities from the ore, the (ii) process is carried out. Flux combines with non-fusible impurities to form (iii). $CaO$ acts as a (iv) flux.

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. (i) - gangue, (ii) -roasting, (iii) - slag, (iv) -acidic

  2. (i) - gangue, (ii) - calcination, (iii) - slag, (iv) - basic

  3. (i) - anode mud, (ii) - leaching, (iii) - matrix, (iv) -acidic

  4. (i) - gangue, (ii) -roasting, (iii) - solution, (iv) -acidic

Show answer
Correct Option: B
Explanation:
$(i)$ The undesired impurities present in the ores are called gangue.
$(ii)$ To remove the volatile impurities from the ore calcination is carried out.
$(iii)$ Flux combines with non-fusible impurities to form slag.
$(iv)$ $CaO$ acts as basic flux.

Extraction of chlorine from brine is based on:

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. reduction

  2. displacement

  3. oxidation

  4. evaporation

Show answer
Correct Option: C
Explanation:
In the extraction of chlorine by electrolysis of brine, oxidation of ${ Cl }^{ - }$ ion to chlorine gas occurs.
$2{ Cl }^{ - }+2{ H } _{ 2 }O\rightarrow 2{ OH }^{ - }+{ H } _{ 2 }+{ Cl } _{ 2 }$

Which of the following is reactions is an example of autoreduction? 

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. $Fe _3O _4+4CO\rightarrow 3Fe+4CO _2$

  2. $CuO+C\rightarrow 2Cu+CO$

  3. $Cu^{2+} _{(aq)}+Fe _{(s)}\rightarrow Cu _{(s)}+Fe^{(2+)} _{(aq)}$

  4. $Cu _2O+\frac{1}{2}Cu _2S\rightarrow 2Cu+\frac{1}{2}SO _2$

Show answer
Correct Option: D
Explanation:

The sulphide ores of certain less electropositive metals like those of Hg, Pb, Cu, etc. when heated in air bring about the conversion of a part of the sulphide ore to oxide or sulphate which then reacts with the remaining sulphide to give the matal and $SO _2$. No external reducing agent is used in this process.
$2Cu _2S+3O _2\rightarrow 2Cu _2O+3SO _2$
$2Cu _2O+Cu _2S\rightarrow 6Cu+ SO _2$

In the process of extraction of gold, Roasted gold ore$+CN^- _{(aq)}+H _2O\overset{O _2}{\rightarrow}[X]+[OH^-]$, $[X]+Zn\rightarrow [Y]+Au$
Identify the complexes [X] and [Y].

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. $[Au(CN) _2]^-, [Zn(CN) _4]^{2-}$

  2. $[Au(CN) _4]^{3-}, [Zn(CN) _4]^{2-}$

  3. $[Au(CN) _2]^{2-}, [Zn(CN) _6]^{4-}$

  4. $[Au(CN) _4]^-, [Zn(CN) _4]^{2-}$

Show answer
Correct Option: A
Explanation:
$4Au+8{ CN }^{ - }+2{ H } _{ 2 }O+{ O } _{ 2 }\longrightarrow 4{ \left[ Au{ \left( CN \right)  } _{ 2 } \right]  }^{ - }+4{ OH }^{ - }$
$2{ \left[ Au{ \left( CN \right)  } _{ 2 } \right]  }^{ - }+Zn\longrightarrow 2Au+{ \left[ Zn{ \left( CN \right)  } _{ 4 } \right]  }^{ 2- }$
It is Mc-Arthur process. Here
$X={ \left[ Au{ \left( CN \right)  } _{ 2 } \right]  }^{ - }$ & $Y={ \left[ Zn{ \left( CN \right)  } _{ 4 } \right]  }^{ 2- }$