Chemistry

Chemical Compounds and Reactions

329 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 chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

The resulting solution obtained at the end of electrolysis of concentrated aqueous solution of $NaCl:$

  1. Turns blue litmus into red

  2. Turns red litmus into blue

  3. Remains colourless with phenolphthalein

  4. The colour of red or blue litmus does not change
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

During the electrolysis of aqueous sodium chloride solution, the products are $NaOH , Cl _2$ and $H _2$.
$NaCl(aq) + H _2O(l) \rightarrow Na^+ (aq) +OH^-(aq) +\frac{1}{2} H _2(g) +\frac{1}{2}Cl _2(g)$
Due to formation of base, it turns res litmus into blue.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Two platinum electrodes were immersed in a solution of $CuSO _4$ and electric current was passed through the solution. After some time, it was found that colour of $CuSO _4$ disappeared with evolution of gas at the electrode. The colorless solution contains:

  1. Platinum sulphate

  2. Copper hydroxide

  3. Copper sulphate

  4. Sulphuric acid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$CuSO _4(aq)\, \xrightarrow{Electrolsis} \, Cu^{2+}(aq)\, +\, SO _4^{2-}(aq)$

At cathode: $Cu^{2+}(aq)\, +\, 2e^-\, \rightarrow\, Cu\, (reduction)$

The blue color of $CuSO _4$ disappears due to the deposition of Cu on Pt electrode.

At anode: $H _2O\, \rightarrow\, 2H^{\oplus}\, +\, 2e^-\, \frac{1}{2} O _2(g)$

Since oxidation potential of $H _2O$ > oxidation potential of $SO _4^{2-}$, so oxidation of $H _2O$ occurs and $O _2(g)$ is evolved at anode.

The colourless solution is due to the formation of $H _2SO _4$ as follows:

$2H^{\oplus}\, (from\, anode)\, +\, SO _4^{2-}\, \rightarrow\, H _2SO _4$

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

In the hardening stage of plaster of paris, the compound formed is :

  1. $CaSO _{4}$
  2. orthorhombic $CaSO _{4} . 2H _{2}O$
  3. $CaSO _{4} . H _{2}O$
  4. monoclinic $CaSO _{4} . 2H _{2}O$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\underset{\text{plaster of paris}}{CaSO _4.1/2H _2O} \xrightarrow[\text{setting}]{H _2O} \underset{\begin{matrix}\text{gypsum}\\text{orthorhombic}\\text{dihydrate}\end{matrix}}{CaSO _4.2H _2O} \xleftarrow[\text{hardening}]{} \underset{\begin{matrix} \text{gypsum} \\text{monoclinic dihydrate}\end{matrix}}{CaSO _4.2H _2O}$
The plaster of paris absorbs water to form orthorhombic calcium sulfate dihydrate which sets to form a hard mass containing monoclinic $CaSO _4.2H _2O$.

Multiple choice chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

Which of the following gives blue flame when burn and is not very soluble in water?

  1. $\displaystyle { O } _{ 2 }$
  2. $\displaystyle { CO } _{ 2 }$
  3. $\displaystyle { N } _{ 2 }$
  4. $\displaystyle { H } _{ 2 }{ SO } _{ 4 }$
  5. $\displaystyle He$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Nitrogen burns with a blue flame and is not very soluble in water.

Multiple choice chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

Which of the following forms a white precipitate when added to a solution of $NaCl$?

  1. $N _2$
  2. $KI$
  3. $CCl _4$
  4. $AgNO _3$
  5. $CaCO _3$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Silver nitrate $\displaystyle AgNO _3$ forms a white precipitate of $AgCl$ when added to a solution of $NaCl$. 

$\displaystyle AgNO _3 + NaCl \rightarrow AgCl \uparrow + NaNO _3$

Multiple choice chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

An orange solid (X) on heating, gives a colourless gas (Y) and a only green residue (Z). Gas (Y) on treatment with Mg, produceds a white solid substance................

  1. $Mg _{3}N _{2}$
  2. $MgO$
  3. $Mg _{2}O _{3}$
  4. $MgCl _{2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$(NH _4) _2Cr _2O _7  \rightarrow N _2 + Cr _2O _3 + 4H _2O$
$3Mg + N _2 \rightarrow Mg _3N _2$
Orange solid is $(NH _4) _2Cr _2O _7$
Colourless gas is $N _2$
Green residue is $Cr _2O _3$

Multiple choice chemistry separation of matter sedimentation, decantation and filtration other methods of separation separation methods

Evaporation of solution of $CuSO _4$ helps in:

  1. making it more concentrated
  2. crystallization of $CuSO _4$
  3. evaporation of salt $CuSO _4$
  4. both $A$ and $B$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

On evaporation of $CuSO _4$ solution, the amount of solvent will decrease and its concentration increases and it will leads to the crystallization of $CuSO _4$.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

Which of the following is the preferred electrolyte for silver plating?

  1. $AgCl+HCl$
  2. $Ag{NO} _{3}+H{NO} _{3}$
  3. ${Ag} _{2}{SO} _{4}$
  4. $AgCN+NaCN$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Silver plating is an electroplating process utilizing an electrolyte containing silver cyanide solution and some free cyanide ions and operating at pH value not less than $8$. Free cyanide prevents precipitation of silver cyanide salt from the solution, provides electrical conductivity of the electrolyte and helps in the dissolution of silver anodes.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

 In the silver plating of copper, $K[Ag(CN) _2]$ is used instead of $AgNO _3$. The reason is:

  1. a thin layer of Ag is formed on Cu

  2. more voltage requirement
  3. $Ag^+$ ions are completely removed from solution
  4. less availability of $Ag^+$ ions, as Cu cannot displace Ag from $[Ag(CN) _2]^-$ ion
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Option D is correct 

less avaibality of $Ag+$ions as, $Cu$ cannot displace $Ag$ from $[Ag(CN) _2]$
$Cu$ can replace $Ag$ in $AgNO _3$. But In coordination compound $Ag$ can't be replaced.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

A solution of ${ AgNO } _{ 3 }$ is a good electrolyte but is not used for electroplating an article with silver because :

  1. rapid deposition of silver takes place resulting in uneven coating

  2. slow deposition of silver takes place resulting in uneven coating

  3. poor conduction of silver

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A solution of $AgNO _3$ is a good electrolyte but is not used for electroplating an article with silver because it undergoes very fast redox process and electroplating done through this process is not uniform.

Multiple choice oxoacids of halogens p- block elements-ii p-block elements the p-block elements chemistry

Bleaching powder and bleach solution are produced on a large scale and is used in several house-hold products. The effectiveness of bleach solution is often measured by iodometry. Bleaching powder contains a salt of an oxoacid as one of its components. The anhydride of that oxoacid is:

  1. $Cl _{2}O$
  2. $Cl _{2}O _{7}$
  3. $ClO _{2}$
  4. $Cl _{2}O _{6}$
  5. $Cl _2O _3$
  6. $Cl _2O _5$
  7. $Cl _3O _9$
  8. $Cl _3O _5$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Bleaching powder is $Ca(OCl)Cl$.


So, bleaching powder contains a salt of $HOCl$.

$Cl _2O$ is an anhydride of $HOCl$.

$Cl _2O+H _2O\Rightarrow 2HOCl$.

Hence, option A is correct.

Multiple choice oxoacids of halogens p- block elements-ii p-block elements the p-block elements chemistry

Select correct statements (s):

  1. $ClO _2\ and \ Cl _2O$ are used as bleaching agents for paper pulp and textiles.
  2. $OCl^-$ salts are used as detergents.
  3. $OCl^-$ disproportionates in alkaline medium.
  4. $BrO^- _3$ is oxidised to $Br^-$ in acidic medium.
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

A. The oxides of chlorine such as $ClO _2$  and $Cl _2O$ are used as bleaching agents for paper pulp and textiles. Thus, the option A is correct.

B. $OCl^-$ salts cannot be used as detergents. Thus, the option B is incorrect.

C. In alkaline medium, $OCl^-$ disproportionates. $3ClO^- \xrightarrow {\Delta} 2Cl^-+ClO _3^-$. Thus, the option C is correct.

D. In acidic medium, $BrO _3^-$ is reduced to $Br^-$. $KBrO _3 + 3H _2SO _3 \rightarrow KBr + 3H _2SO _4$ Thus, the option D is incorrect.

Multiple choice oxoacids of halogens p- block elements-ii p-block elements the p-block elements chemistry

Bleaching action of $CaOCl _2$ is due to :

  1. Nascent oxygen
  2. $Ca$
  3. $Cl$
  4. $HCl$
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

Calcium oxychloride ($CaOCl _2$) is known as bleaching powder. When it is treated with excess of dilute acids, chlorine is evovled which is responsible for the bleaching action of bleaching powder. Due to the evolution of nacent oxygen, it acts an an oxidising and bleaching agent.

Multiple choice oxoacids of halogens p- block elements-ii p-block elements the p-block elements chemistry

Bleaching powder loses its power on keeping for long time because :

  1. it changes to calcium hypochlorite.

  2. it changes to calcium chloride and calcium hydroxide.

  3. it absorbs moisture.

  4. it changes to calcium carbonate and chlorine.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bleaching powder reacts with carbon dioxide in air to give chlorine and calcium carbonate.

$2Ca(ClO) _2 + 2CO _2 \rightarrow 2CaCO _3 + 2Cl _2 + O _2$