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 p- block elements-i study of aluminium chloride study of aluminium structure of some compounds

An inorganic compound $A$ shows the following reaction:
(i) It is white solid, exists as dimer and fumes in the wet air.
(ii)It sublimes at $180^{ \circ  }C$ and forms monomer if heated to $400^{ \circ  }C$.
(iii) Its aqueous solution turns blue litmus to red and gives a white precipitate with $AgNO _3$ solution, which is soluble in $NH _4OH$.
Addition of $NH _4OH$ and NaOH separately to the solution of $A$ gives a gelatinous precipitate which in however soluble in excess of $NaOH$.
The compound $A$ is:

  1. $Al(OH) _3$
  2. $Al _2Cl _6$
  3. $Al _2O _3$
  4. $Al _2(SO _4) _3$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

(B) Compound $B$ is ${Al} _{2}{Cl} _{6}$.

(i) ${Al} _{2}{Cl} _{6}$ is a white solid, exists as dimer and fumes in wet air.
(ii) It sublimes at 180°C and converts into $Al{Cl} _{3}$ at 400°C.
(iii) Its aqueous solution is acidic, so it turns blue litmus to red.
${Al} _{2}{Cl} _{6} + 6{H} _{2}O \; \longrightarrow \; \underset{\text{(weak base)}}{2Al{(OH)} _{3}} + \underset{\text{(strong acid)}}{6HCl}$.
It gives white ppt. with $AgN{O} _{3}$ which is soluble in $N{H} _{4}OH$.
(iv)$Al{Cl} _{3} + 3NaOH \; \longrightarrow \; \underset{\text{(white ppt.)}}{2Al{(OH)} _{3}} + 3NaCl$
$Al{(OH)} _{3} + \underset{\text{(excess)}}{NaOH} \; \longrightarrow \; \underset{\text{(soluble)}}{NaAl{O} _{2}} + 2{H} _{2}O$
But in case of $N{H} _{4}OH$, the ppt. of $Al{(OH)} _{3}$ does not dissolve in excess of $N{H} _{4}OH$.

Multiple choice evs animals- nature's gift animal and habitat wonderful world of bholu food material and source

Sealing wax is

  1. Vegetable wax

  2. Hard paraffin wax

  3. Shellac

  4. Lanolin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sealing wax is a wax material of a seal which, after melting, hardens quickly forming a bond that is difficult to separate without noticeable tampering. Typically these are a mixture of wax and resin; usually beeswax and shellac.

So, the correct answer is 'Shellac'.

Multiple choice chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

While obtaining pure copper sulphate by crystallization, the solution is saturated is indicated by :

  1. change in color

  2. change in consistency

  3. formation of bubbles

  4. formation of crystals near rod
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

During purification of copper sulphate by crystallization, the impure sample is mixed with water and then heated to saturation. The saturation is indicated by dipping glass rod in solution from time to time. Small crystals are formed near the glass rods which indicates saturation.

Multiple choice chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

Copper sulphate crystals are of which color after purification?

  1. White

  2. Black

  3. Blue

  4. Yellow
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

To crystallise copper sulphate, it is dissolved in water and a small quantity of dilute sulphuric acid is added to prevent the hydrolysis of copper sulphte. The impurities left behind in the solution are removed by filtration. The filtrate is concentrated to the crystallisation point and then cooled. On cooling, transparent blue crystals of copper sulphate separate.

Multiple choice chemistry separation of matter crystals and crystallisation filtration and crystallisation other methods of separation

Crystals can be grown by _________.

  1. cooling a saturated solution

  2. heating a saturated solution

  3. stirring a saturated solution

  4. planting in a well watered fertile soil
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Cooling a saturated solution. (Heating is stopped at the point when a hot saturated solution is formed. If the resulting solution is allowed to cool to room temperature, the dissolved solid will precipitate out as pure crystals.)

Multiple choice chemistry air and water pollution control smoke, dust and other air pollutants, acid rain air pollutants and its effects air and air pollution

What is the odour of $H _2S$?

  1. Rotten fish

  2. Rotten egg

  3. Pungent

  4. Rotten cabbage
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hydrogen sulfide is the chemical compound with the formula $H _2S$. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs. It is very poisonous, corrosive, and flammable.

Option (B) is the answer.

Multiple choice botany living world of plants - plant physiology historical events in photosynthesis history of photosynthesis introduction to photosynthesis

The term dephlogisticated air was given by

  1. Von Mayer

  2. Van Helmont

  3. Warburg

  4. Priestely
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The term dephlogisticated air was given by Priestely. He performed the experiment to prove that the plants are responsible for the recycling of the gas present in the air which is used during burning and respiration. 
The experiments which were performed are as follows:
1) There was a bell-shaped jar placed upon a burning candle and a live mouse.
2) When the mouse and the candle were placed under the bell jar, the mouse used all the oxygen from the air. This resulted in the extinguishing of the candle due to the absence of oxygen in the air.  The mouse also dies after some time due to the absence of oxygen. 
3) Then a mint plant was placed in the bell jar along with a live mouse and the burning candle. 
4) The plant help in recycling the oxygen in the air by using carbon dioxide. This causes the replenishing of the oxygen in the air which is lost by the respiration by mouse and the burning of the candle.

Thus, the plant can perform photosynthesis and replenish the oxygen in the air which is used by the animals for breathing. 
Multiple choice chemistry p- block elements-ii hydrogen chloride chlorine - 17 group p-block elements

When three parts of conc. HCl and one part of conc. $HNO _{3}$ is mixed, a compound 'X' is formed. The correct option related to 'X' is:

  1. 'X' is known as aqua-regia

  2. 'X' is used for dissolving gold

  3. 'X' is used for decomposition of salts of weaker acids

  4. both (a) and (b)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aqua regia is also called as royal water is a mixture of nitric acid and hydrochloric acid in the  molar ratio of 1:3. Aqua regia is a yellow-orange fuming liquid.Aqua regia is used for the decomposition of weak acids.

Hene option D is correct.

Multiple choice chemistry p- block elements-ii hydrogen chloride chlorine - 17 group p-block elements

There are two colourless solutions (A) and (B), both give white ppt with $AgNO _3$ which dissolves in $aq \, NH _3$. Also (A) on reaction with $H _2O$ gives orange turbidity while (B) gives white turbidity. Identify (A) and (B). 

  1. (A) $SbCI _3 ;\, \, \,$ (B) $BiCI _3$
  2. (A) $BiCI _3 ;\, \, \,$ (B) $SbCI _3$
  3. (A) $SeCI _3; \, \, \,$ (B) $BiCI _3$
  4. (A) $BiCI _3; \, \, \,$ (B) $SeCI _3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$SbCI _3$ or $BiCI _3 + AgNO _3 \longrightarrow \underset {white\, \, ppt }{ AgCI\downarrow}$ (due to $CI^-$)

              $AgCI + 2NH _3 (aq) \longrightarrow [\underset{soluble}{Ag(NH _3) _2}] CI$

                      $SbCI _3 + H _2O \longrightarrow \underset{orange}{SbOCI}\downarrow + 2HCI$

                  $SbOCl + 2HCI \longrightarrow \underset{soluble}{SbCI _3}+H _2O$

                      $BiCI _3 + H _2O \longrightarrow \underset{white}{BiOCI\downarrow}+ 2HCI$

                  $BiOCI + 2HCI \longrightarrow \underset{soluble}{BiCI _3}+H _2O$
Turbidity can be dissolved in dil. $HCl$.

Multiple choice chemistry p- block elements-ii hydrogen chloride chlorine - 17 group p-block elements

Aqua-regia dissolves gold. 
which is correct?

  1. Aqua regia, or nitro-hydrochloric acid is a highly corrosive mixture of acids , a fuming yellow or red solution.

  2. The mixtures is formed by freshly mixing concentrated nitric acid and hydrochloric acid hoptimally in a volume ratio of 1:3.

  3. it can dissolve the noble metalsgold and platinum

  4. all of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aqua regia, or nitro-hydrochloric acid is a highly corrosive mixture of acids, a fuming yellow or red solution. The mixtures is formed by freshly mixing concentrated nitric acid and hydrochloric acid hoptimally in a volume ratio of 1:3. It was named so because it can dissolve the noble metalsgold and platinum
Hence answer 1 is correct.

Multiple choice chemistry p- block elements-ii hydrogen chloride chlorine - 17 group p-block elements

    Appearance  Reaction with dilute $HCl$  Reaction with dilute $HNO _3$
 Unknown metal #1  Dull gray solid with white oxide coating Dissolved with bubbles of clear gas   Dissolved with bubbles of clear gas
 Unknown metal #2  Solid; lustrous, smooth silver-gray surface  No reaction  Dissolved with bubbles of orange gas

Identify metal #1.

  1. Mercury

  2. Copper

  3. Zinc

  4. Iron

  5. Silver
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Zinc being an active metal readily reacts with hydrochloric acid at room temperature to form soluble zinc chloride and hydrogen.

   $Zn+2{ H }Cl\rightarrow Zn{ Cl } _{ 2 }+{ H } _{ 2 }$
Zinc reacts with dilute nitric acid  and libreates nitric oxie.
$3Zn+{ 8HNO } _{ 3 }\rightarrow { 3Zn(NO _{ 3 }) } _{ 2 }+4{ H } _{ 2 }O+2NO$