Tag: chemistry

Questions Related to chemistry

Which of these are spontaneous at higher temperature?

I : $2CuS\, +\, C\, \rightarrow\, 2Cu\, +\, CS _2$ 

II : $ 2CaS\, +\, C\, \rightarrow\, 2Ca\, +\, CS _2$ 

III : $ 2CuS\, +\, 3O _2\, \rightarrow\, 2CuO\, +\, 2SO _2$

Given that : $\Delta\,G^{\circ} _f$ (in $kJ$.$mol^{-1}$) for $CuS\, =\, -49$; $CS _2\, =\, 63.6$ ;  $CaS\, =\, -1320$; $CuO\, =\, -127.2$ and $SO _2\, =\, -300.4$ 

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. $2CuS\, +\, C\, \rightarrow\, 2Cu\, +\, CS _2$

  2. $ 2CaS\, +\, C\, \rightarrow\, 2Ca\, +\, CS _2$

  3. $ 2CuS\, +\, 3O _2\, \rightarrow\, 2CuO\, +\, 2SO _2$

  4. None of these

Show answer
Correct Option: A,B,C

Consider the following steps:

$CuS\,\overset{roast\,\,in\,\,air}{\rightarrow}\,(A)\, \overset{roast\,\,without\,\,air}{\rightarrow}\,(B)$

Which are the correct statements?

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. It is self-reduction

  2. It involves disproportionation: $Cu _2S\,\rightarrow\,Cu\,+\,CuS$

  3. (A) is a mixture of $Cu _2O$  and $SO _2$ and (B) is $Cu$ and $SO _2$

  4. (A) is a mixture of $Cu$ and $SO _2$ and (B) is $CuSO _4$

Show answer
Correct Option: A,C
Explanation:

Self-reduction of CuS to Cu can be carried out in either Bessemer converter or Pierce-Smith converter.

$2Cu _2S+3O _2 \rightarrow \underset {A} { 2Cu _2O + 2SO _2}$

$2Cu _2O+Cu _2S \rightarrow \underset {B} { 6Cu+SO _2}$

(A) is a mixture of $Cu _2O$  and $SO _2$ and (B) is  Cu and $SO _2$.

Lead metal is purified by electrolysis in a similar manner to copper; the electrolyte is lead (II) hexafluorosilicate $PbSiF _6$.
chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. True

  2. False

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Correct Option: A
Explanation:

Lead metal is purified by electrolysis in a similar manner to copper, the electrolyte is Lead $(II)$ hexa Fluorosilicate $PbSiF _6$. The given statement is True.

A solution of Lead-Fluorosilicate containing an excess of fluorosilicic acid has been found to work satisfactorily as an electrolyte for refining lead. 

Froth-flotation process can be made more effective by the:

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. use of pine oil which produces stable froth

  2. use of sodium ethyl xanthate as a collector that coats the particles of ore

  3. both (a) and (b)

  4. none of the above

Show answer
Correct Option: C
Explanation:

Pine oil acts as foaming agent. It stabilizes the froth.
Sodium ethyl xanthate (also potassium ethyl xanthate) acts as collectors.
They coat the ore particles.

Which of the following statement is correct?

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. Froth flotation method can only be used for sulphide ore

  2. Tin stone consists of wolframite as non-magnetic impurity

  3. In cyanide process for the extraction of silver, Zn is used as leaching agent

  4. Bessemerization process is used in the extraction of copper from copper pyrite

Show answer
Correct Option: A,D
Explanation:

(A) Froth floatation method is used for concentration of sulphide ores such as galena $(PbS)$, zinc blende $(ZnS)$ and copper pyrites $(CuFeS _2)$.


(B) Tin stone consists of wolframite as magnetic impurity and stannic oxide as a non-magnetic impurity.

(C) In the cyanide process for the extraction of silver, Zn is used as leaching agent.
The ore containing silver or gold is leached with a dilute solution of NaCN or KCN in the presence of air. 


(D) Bessemerization process is used in the extraction of copper from copper pyrite.

The reactions involved in the process are given below.
$\displaystyle 2Cu _2S + 3O _2 \rightarrow 2Cu _2O + 2SO _2 \uparrow $
$\displaystyle 2Cu _2O + Cu _2S \rightarrow 6Cu + SO _2 \uparrow $

Thus, the options (A) and (D) are correct.

Copper is extracted from copper pyrites. After roasting, the ore is mixed with silica and coke and then smelted in a blast furnace. The matte obtained from the blast furnace is charged into a silica lined converter. Some silica is also added and a hot air blast is thrown into the mixture to obtain blister copper which is purified by electrorefining.


During roasting, copper pyrites are ultimately converted into a mixture of:

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. $FeS + Cu _2S$

  2. $FeS + Cu _2O$

  3. $FeO + Cu _2S$

  4. $FeS+Cu _2S \rightarrow FeO+Cu _2O$

Show answer
Correct Option: D
Explanation:
Process:
Copper pyrites contains only 2-3% of copper. The rest of ore contains iron as sulphide, silica, silicious materials, sulphur, arsenic etc as impurities. Froth floatation is carried out by xanthate and pine oil. The froth is collected and dried when concentrated ore is obtained which contains 25-30% of Cu. Then smelting of the roasted ore in blast furnace is done.

The minor reactions that occured during roasting continue here. Ferrous oxide combines with sand to form a fusible slag. Cuprous oxide formed combines with ferrous sulphide to give ferrous oxide and cuprous sulphide. This is because iron has more affinity for oxygen than copper. 
$FeO + SiO _2 \rightarrow FeSiO _3$

During roasting, copper pyrite converts into a mixture of 
$FeS+Cu _2S \rightarrow FeO+Cu _2O$

Silica is added to roasted copper ores during smelting in order to remove:

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. Cuprous sulphide

  2. Ferrous oxide

  3. Ferrous sulphide

  4. Cuprous oxide

Show answer
Correct Option: B
Explanation:

Silica is added to roasted copper ores during smelting in order to remove $FeO$ (ferrous oxide) as $FeSiO _3$ (slag).

$FeO + SiO _2 \rightarrow FeSiO _3$

Anode mud obtained after electrolytic refining of copper contains:

chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

  1. $Ag$

  2. $Au$

  3. $Pt$

  4. All of the above

Show answer
Correct Option: D
Explanation:
Electrorefining:
Anode: Impure copper or crude copper
Cathode: Pure copper
Electrolyte: 15% $CuSO _4$ Solution + 5% $H _2SO _4$

When electric current is passed through the electrolyte, the anode gradually dissolves and pure copper is deposited on the cathode which gradually grows in size. Impurities like. Fe, Zn, Ni etc, dissolve in the solution as sulphates while gold, silver, platinum settle down below the anode as anode mud.

What does a catalyst do?

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. Alter the state of equilibrium.

  2. Decreases the activation energy.

  3. Increases collision frequency.

  4. Increases the average kinetic energy of reacting species.

Show answer
Correct Option: B
Explanation:

Catalyst is a substance, which lowers the activation energy of reaction because it provides an alternate pathway for reaction. Also, it increases backward and forward reaction to the same extent. Due to this lower activation energy, equilibrium is attained faster.

Which of the following are electrophiles?

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. $BF _3$

  2. $: CCl _2$

  3. $^{\oplus}NH _4$

  4. $I^{\ominus}$

Show answer
Correct Option: C