Tag: chemistry

Questions Related to chemistry

Which of the following is a limitation of the law of constant composition is not applicable?

chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions

  1. When same isotopes of an element take part in the formation of a particular compounds.

  2. When different isotopes of different elements take part in the formation of a particular compound.

  3. When different isotopes of an element take part in the formation of a particular compound.

  4. None of the above.

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Correct Option: C
Explanation:
Law of constant composition is not applicable if an element exists in different isotopes which may be involved in the formation of the compound. The elements may combine in the same ratio but the compounds formed may be different.

Hence, the correct option is $(C)$
Assertion (A): Pure water obtained from different sources such as a river, well, spring, the sea always contains hydrogen and oxygen in the ratio of 1:8 by mass.

Reason (R): The total mass of reactants and products during chemical or physical change is always the same.
chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions

  1. Both A and R are true and R is the correct explanation of A

  2. Both A and R are true and R is not correct explanation of A

  3. A is correct and R is incorrect

  4. A is incorrect and R is correct

Show answer
Correct Option: A

Statement: Every nine parts of water by weight contain eight parts by weight of oxygen. 


State whether the given statement is true or false.

chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions

  1. True

  2. False

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Correct Option: A

Blister copper obtained during extraction from cuprous oxide is called so because:

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

  1. it has blister like eruptions due to evolution of gas

  2. it has a shining surface like blister

  3. it is the most impure form of copper

  4. its surface is uneven due to different thickness at different place

Show answer
Correct Option: A
Explanation:

The various reaction involved in extraction of copper from cuprous oxide are:
$2FeS+3O _2 \rightarrow 2FeO+2SO _2$
$FeO+SiO _2 \rightarrow FeSiO _3$
$2Cu _2S+3O _2 \rightarrow 2Cu _2O+2SO _2$
$2Cu _2O+Cu _2S \rightarrow 6Cu+SO _2$
The solidified copper obtained has blistered appearance due to the evolution of $SO _2$ and so it is called blister copper.

Why is partial roasting of sulphide ore done in metallurgy of copper?

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

  1. Auto-reduction of $CuO$ formed is carried out by remaining $CuS$ in the reaction.

  2. $Cu$ is separated out by partial reduction due to sedimentation.

  3. Due to difference in gravity $CuO$ and $CuS$ are separated.

  4. Complete roasting cannot be done in one step hence partial roasting is done.

Show answer
Correct Option: A
Explanation:

Partial reduction of Sulphide ores gives copper oxide which further reacts with copper sulphide to show an auto reduction.

$2CuS+3O _2\longrightarrow 2CuO+2SO _2$
$2CuO+CuS\overset {Autoreduction}{\longrightarrow}3Cu+SO _2$

Blister copper is:

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

  1. impure copper

  2. obtained in self-reduction process during bessemerisation

  3. both are correct

  4. none is correct

Show answer
Correct Option: C
Explanation:

Blister copper is a form of a impure copper which is obtained in self reduction process during bessemerization.

Reactions take place in blast furnace-
$2Cu _2O+Cu _2S\longrightarrow 6Cu+SO _2$
The molten metal is cooled in sand moulds $SO _2$ escapes. The impure copper metal is known as "Blister copper" and is about $98\%$ pure.

Following reactions take place during extraction of gold.
$4Au+8CN^-+2H _2O+O _2\rightarrow 4[Au(CN) _2]^-+4OH^-$
$2[Au(CN) _2]^-+Zn\rightarrow 2Au+[Zn(CN) _4]^{2-}$
Zinc in the extraction of gold acts as a/an:

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

  1. oxidising agent

  2. flux

  3. reducing agent

  4. decomposing agent

Show answer
Correct Option: C
Explanation:
$4Au+8CN^-+2H _2O+O _2\longrightarrow 4[Au(CN) _2]^-+4OH^-$
$2[Au(CN) _2]^-+Zn\longrightarrow 2Au+[Zn(CN) _4]^{2-}$
                                 $0$                        $+2$
In the above reaction, Zinc is changing its states from $0$ to $+2$ so zinc is getting oxidized and it acts as reducing agent.

Mark the incorrect statement.

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

  1. Copper is extracted by smelting in a reverberatory furnace.

  2. Zinc is extracted by reduction of oxide with aluminum.

  3. Aluminium is extracted by electrolysis of its oxide.

  4. Iron is extracted by reduction of its oxide in blast furnace.

Show answer
Correct Option: B
Explanation:
It is not profitable method for extraction of Zinc. Zinc is extracted by distillation and by electrolytic refining. So, it is not extracted by reduction of oxide with Aluminium.

Which of the following metals is extracted using a silica lined convertor?

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

  1. $Mg$

  2. $Al$

  3. $Cu$

  4. $Zn$

Show answer
Correct Option: C
Explanation:

During the extraction of copper from cuprous oxide $(copper[I]oxide)$ the ore is heated in a reverberatory furnace after mixing with silica. In the furnace, iron oxide, slag of iron silicate and copper is produced in the form of copper matte. This contains $Cu _2S$ and $FeS$.

$FeO+SiO _2\longrightarrow \underbrace {FeSiO _3} _{(slag)}$
Copper matte is then charged into silica lined converter. Some silica is also added and hot air blast is blown to convert the remaining $FeS _2, FeO$ and $Cu _2S/Cu _2O$ to metallic copper.

Zinc is refined by :

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

  1. Liquation (or) distillation under reduced pressure

  2. Electrolytic method or polling

  3. Liquation or electrolytic method

  4. Distillation under reduced pressure or electrolytic method

Show answer
Correct Option: D
Explanation:

Zinc is refined by distillation under reduced pressure or electrolytic method. Distillation is very useful for low boiling metals like zinc and mercury. The impure metal is evaporated to obtain the pure metal as distillate.