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

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

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $(C)$
Multiple choice chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions
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.

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Assertion states the law of definite proportions, which is true for pure water regardless of source. Reason states the law of conservation of mass, which is also a true chemical principle. However, the constant composition by mass is not explained by the conservation of mass during reactions.

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

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


State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Water (H2O) has a molar mass of 18 g/mol (2*1 + 16). The mass ratio of oxygen to water is 16/18, which simplifies to 8/9. Thus, 9 parts of water contain 8 parts of oxygen.

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

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

Blister copper is:

  1. impure copper

  2. obtained in self-reduction process during bessemerisation

  3. both are correct

  4. none is correct
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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:

  1. oxidising agent

  2. flux

  3. reducing agent

  4. decomposing agent
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

Mark the incorrect statement.

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

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

  1. $Mg$
  2. $Al$
  3. $Cu$
  4. $Zn$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Zinc is refined by :

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.