Chemistry

Chemical Compounds and Reactions

505 Questions

Chemical compounds and reactions involve understanding the properties, colors, and formation of various chemical substances. Questions focus on identifying precipitates, observing color changes during reactions, and naming common compounds. This topic is a fundamental part of the chemistry syllabus for competitive exams.

identifying precipitateschemical reaction colorscompound namingcolloidal particle propertiesacid base reactions

Chemical Compounds and Reactions Questions

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

$90-$ Octane Petrol is a rating that indicates that the petrol in the engine would not waster its energy in making a 'knocking sound', but would rather use its energy efficiency to maintaining speed for travel $'90-Octane$ petrol' means that the petrol is as good as:

  1. $90$% octane
  2. $90$% normal heptane and $10$% iso-octane
  3. A mixture of $90$% iso-octane and $10$% normal (straight chain) heptane
  4. $90$% petrol
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

90-Octane petrol is the  mixture of 90% iso-octane and 10% normal (straight chain) heptane.

Hence option C is correct.

Multiple choice imperfections in solids solid state the solid state chemistry

Silver halides generally show ?

  1. Schottky defect

  2. Frenkel defect

  3. both Frenkel and Schottky defects

  4. cation excess defect
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Silver halides show both Frenkel and Schotkky defects. For Frenkel defect the reason is that there is size difference between the sizes of silver and halide.

Schottky defect is possible because silver halides are highly ionic.
So, correct answer is option C.

Multiple choice imperfections in solids solid state the solid state chemistry

An excess of potassium ions makes KCl crystals appear violet or Lilac in colour since

  1. some of the anionic sites are occupied by an unpaired electron

  2. some of the anionic sites are occupied by a pair of electrons

  3. there are vacancies at someanionic sites

  4. F-centres are created which impart colour to the crystals
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

When KC1 is heated in vapour of K, some of the Cl leave their lattice site and create anion vacancies. This chloride ion wants to combine with K vapour to form potassium chloride. For doing so K atom loses electrons form K ions. This released electron diffuses into the crystal to get entrapped in the anion vacancy called F-centre. When visible light falls on the crystal, this entrapped electron gains energy, goes to the higher level when it comes back to the ground state, energy is released in the form of light.

Multiple choice imperfections in solids solid state the solid state chemistry

The appearance of colour in solid alkali metal halides is generally due to: 

  1. schottky defect

  2. frenkel defect

  3. interstitial position

  4. F-centre
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In F-centre defect in which an anionic vacancy in a crystal is filled by one or more unpaired electron. These electron absorb light in the visible region and emits colour. So, appearance of colour in solid alkali metal halides is generally due to F-centre.

Multiple choice imperfections in solids solid state the solid state chemistry

Statement-I:  Solids having more $F-$centres possess intense colours.

Statement-II:  Excess of $Na^{+}$ in $NaCl$ solid having F-centres makes it appear to pink.

  1. Statement-I is correct but Statement-II is wrong

  2. Statement-I is wrong but Statement-II is correct

  3. Both Statement-I and Statement-II are correct and Statement-II is correct explanation of Statement-I

  4. Both Statement-I and Statement-II are correct but Statement-II is not correct explanation of Statement-I
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

F-centres are indeed responsible for the intense colors in alkali halides due to the excitation of trapped electrons. However, the color of NaCl with F-centres is yellow, not pink, making statement II incorrect.

Multiple choice imperfections in solids solid state the solid state chemistry

Crystals have 'vacant sites' or 'defects' in them. When light strikes a photographic silver bromide paper, silver atoms move in through these defects to:

  1. develop the film

  2. form tiny clumps of silver atoms

  3. form negative images

  4. form a colour image
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When light strikes a photographer $(AgBr)$ paper, it gives energy to the electrons present in the film. These energetic electrons when strike silver ions turn them to silver atoms. So eventually,  ions leave their lattice site and occupy interstitial sites. Since silver atoms are black in color so whenever light strikes a silver ion the photographic film will turn black.

Multiple choice chemistry general principles of metallurgy concentration of ore concentration of ores principles of metallurgy

When $ZnS$ and $PbS$ minerals are present together, then $NaCN$ is added to separate them in the froth flotation process as a depressant, because:

  1. $Pb(CN) _2$ precipitated while no effect on $ZnS$
  2. $ZnS$ forms soluble complex $Na _2 Zn(CN) _4$
  3. $PbS$ forms soluble complex $Na _2Pb(CN) _4$
  4. both $(a)$ and $(b)$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$NaCN$ prevents $ZnS$ from forming the froth by reacting with it to from complex $Na _2[Zn(CN) _4]$ and acts as a depressant. While it does not prevent $PbS$ from forming froth and both the ores can easily be separated.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

A mixture of boron trichloride and hydrogen is subjected to silent electric discharge to form $'A'$ and $HCl. 'A'$ is miced with $NH _3$ and heated to $200^oC$ to form $'B'$. The formula of $'B'$ is

  1. $H _3BO _3$
  2. $B _2O _3$
  3. $B _2H _6$
  4. $B _3N _3H _6$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$2BCl _3+3H _2\underset {discharge}{\xrightarrow {electric}}\underset {(A)}{B _2H _6}+6HCl$.


$A$  is $B _2H _6$

$3B _2H _6+6NH _3\rightarrow 2B _3H _6N _3 + 12H _2$

So $B$  is $B _3N _3H _6$.

Hence option D is correct

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

A compound $A$ of boron reacts with $NMe _3$ to give an adduct $B$ which on hydrolysis gives a compound $C$ and a gas $D$. Compound $C$ is an acid.


Gas $D$ is :

  1. hydrogen

  2. oxygen

  3. water

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Since compound $'A'$  of Boron reacts with ${ NMe } _{ 3 }$  to form an adduct $'B'$.  Thus compound $'A'$ is lewis acid.  Hydrolysis of $'B'$ gives  an acid $'C'$ and hydrogen gas.

 Diborane  $(A)$ ${ B } _{ 2 }{ H } _{ 6 }+{ 2NMe } _{ 3 }\longrightarrow { 2BH } _{ 3 }\cdot { NMe } _{ 3 }$  Adduct  $(B)$

${ BH } _{ 3 }\cdot { NMe } _{ 3 }+3{ H } _{ 2 }O\longrightarrow { H } _{ 3 }{ BO } _{ 3 }+{ NMe } _{ 3 }+6{ H } _{ 2 }$  Boric Acid $(C)$
Multiple choice chemistry chemistry of non-metals oxides of elements simple oxides oxygen

$K0 {2}$(potassium super oxide) is used in oxygen cylinder in space and submarines. This is because it ____________.

  1. absords $CO _{2}$ and increase $O _{2}$ content

  2. eliminates moisture
  3. absords $CO _{2}$

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

Because it absorbs $CO _2$ and increases $O _2$ concentration according to the following reaction

$4K{ O } _{ 2 }+2{ CO } _{ 2 }\rightarrow 2{ K } _{ 2 }{ CO } _{ 3 }+3{ O } _{ 2 }$

Multiple choice chemistry preparation of gases nitrogen gas component of air - nitrogen nitrogen

On heating ammonium dichromate and barium azide separately we get:

  1. $N _{2}$ in both cases
  2. $N _{2}$ with ammonium dichromate and $NO$ with barium azide
  3. $N _{2}O$ with ammonium dichromate and $N _{2}$ with barium azide
  4. $N _{2}O$ with ammonium dichromate and $NO _{2}$ with barium azide
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

On heating ammonium dichromate and barium azide separately we get $N _2$ in both cases.

$(NH _4) _2Cr _2O _7 \rightarrow Cr _2O _3 + 4H _2O +N _2$.

$Ba(N _3) _2 \rightarrow Ba + 3N _2$.

Hence option A is correct.