Chemistry

Chemical Reactions and Equations

674 Questions

Chemical reactions and equations form a foundational chemistry topic where students identify reaction products, balance chemical formulas, and classify reaction types. It covers critical mechanisms like Markovnikov's rule, precipitation, and endothermic or exothermic processes. These questions are highly common in general science sections of state and central government competitive exams.

Endothermic reactionsPrecipitation reactionsDehydrohalogenation of alkyl halidesChemical equation balancingReaction product identification

Chemical Reactions and Equations Questions

Multiple choice reactions of haloarenes haloalkanes and haloarenes chemistry

Grignard reagent is usually prepared by :

$R-X+Mg\xrightarrow {E{ t } _{ 2 }O} RMgX$               Grignard reagent

$Ar-X+Mg\xrightarrow {E{ t } _{ 2 }O} ArMgX$           Grignard reagent

Grignard reagent acts as a strong base. Grignard reagent carry out nucleophilic attack in absence of acidic hydrogen. Grignard reagent form complex with its ether solvent. Complex formation with molecule of ether is an important factor in the formation and stability of Grignard reagent.

Which of the following Grignard reagents are not possible ?

  1. $HS - CH _{2} - CH _{2} - CH _{2}MgBr$
  2. $HO - CH _{2} - CH _{2} - CH _{2}MgBr$
  3. $NH _{2} - CH _{2} - CH _{2} - CH _{2}MgBr$

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

(A)$\overset {\delta +}{H}-S-CH _2CH _2CH _2-MgBr \xrightarrow [reaction]{acid-base} BrMgS-CH _2CH _2CH _3$


(B) $H-O-CH _2CH _2CH _2MgBr \xrightarrow [reaction]{acid-base} BrMgO-CH _2CH _2CH _3$


(C) $\overset {\delta +}{H}-\underset {|}{N}-CH _2CH _2-CH _2-MgBr \xrightarrow [reaction]{acid-base} BrMg-\underset {|}{N}-CH _2CH _2CH _3$
         $\delta^+ H$                                                                                        $H$

So, all of these Grignard reagent can take their own acidic hydrogen. Therefore all of these Grignard reagents are not possible.

Multiple choice reactions of haloarenes haloalkanes and haloarenes chemistry

Which of the following Grignard reagent can be prepared? 

  1. $Br-Mg-{CH} _{2}-{CH} _{2}-{CH} _{2}O-H$
  2. $Br-Mg-{CH} _{2}-{CH} _{2}-SH$
  3. $BrMg-{CH} _{2}-{CH} _{2}-{NH} _{2}$
  4. $BrMg - CH _2- CH _2 - \underset{CH _3}{\underset{|}{N} -} CH _3$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Grignards reagent form via the reaction of an alkyl or aryl halide with magnesium metal.The reaction is conducted by adding the organic halide to a suspension of magnesium in an ethyal solugnt,which produce the reaction proceeds through a single electron transfer as:
$R-X+mg\longrightarrow R-X^-+Mg^+$
$R-X^-\longrightarrow R+X^-$
$R+Mg^+\longrightarrow RMg^+$
$RMg^++X^-\longrightarrow RMgX$
Thus,by the above way of preparing grignard reagent,compounds with carbonyl group $(C=O)$,$-SH$ group and $-NH _2$ group cannot be prepared .
Multiple choice reactions of haloarenes haloalkanes and haloarenes chemistry

In which of the following reactions, products are not correctly matched in:

  1. $RMgX +{CO _{2}}\xrightarrow[(ii)H^{\bigoplus }]{(i)CO _{2}}$Carboxylic acid
  2. $RMgX + C _{2}H _{5}OH \rightarrow$ Alkane
  3. $RMgX+CH _{3}CH _{2}Cl\rightarrow$ Alkene

  4. <span class="MathJax_Preview">
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Reaction:
$RMgX+CH _{3}CH _{2}Cl\rightarrow R-R$ alkane.

Multiple choice reactions of haloarenes haloalkanes and haloarenes chemistry

Propane dithioic acid is prepared by which of the following reactions, followed by hydrolysis:

  1. ${C} _{3}{H} _{7}MgBr+{CS} _{2}$
  2. ${C} _{2}{H} _{5}MgBr+{CS} _{2}$
  3. ${C} _{3}{H} _{7}MgBr+{SO} _{2}$
  4. ${C} _{2}{H} _{5}MgBr+{SO} _{3}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Propane dithioic acid is prepared by the reaction of the following, followed by hydrolysis of ${C} _{2}{H} _{5}MgBr+{CS} _{2}$
Hence option B is correct.
Multiple choice redox and stoichiometry applications of redox reaction oxidation- reduction reactions redox reactions chemistry

A volume of $100 ml$ of $ H _{2}O _{2}$ is oxidized by 100 ml of $ 1 M \ KMnO _{4}$ in acidic medium $ (MnO _{4}^{-}$ reduced to $ Mn^{2+}).$ A volume of $100 ml$ of same $H _{2}O _{2}$ is oxidized by $'V'$ ml of $1 M \ KMnO _{4}$ in basic medium ($ MnO _{4}^{-}$ reduced to $ MnO _{2}).$ The value of $'V'$ is

  1. $500$
  2. $100$
  3. $33.33$
  4. $166.67$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In acidic medium, 

$ N _{1}V _{1} = N _{2}V _{2} $

$ n _1\times M _{1}\times V _{1} = n _2\times M _{2}\times V _{2} $

$ 5\times 1\times 100 =  2\times M _{2} \times 100$ 

$ M _{2} = 2.5\,M $

Now in basic medium,

$ N _{1}V _{1} = N _{2}V _{2} $

$ 2\times 2.5 \times 100=  3\times 1\times V $

$ \therefore V = \dfrac{200\times 2.5}{3} $

$V = 166.66\,ml $

Multiple choice redox and stoichiometry applications of redox reaction oxidation- reduction reactions redox reactions chemistry

Write balanced half reactions for the following redox reaction:
$Cr _2O _7^{2-} + Fe^{2+}\rightarrow  Cr^{3+} + Fe^{3+}$

  1. Reduction: $6e^-+ 14H^+ + Cr _2O _7^{2-} \rightarrow Cr^{3+} + 7H _2O $

    Oxidation: $ \\ Fe^{2+} \rightarrow Fe^{3+} + e^{-}$
  2. Oxidation: $6e^-+ 14H^+ + Cr _2O _7^{2-} \rightarrow Cr^{3+} + 7H _2O $

    Reduction: $ \\ Fe^{2+} \rightarrow Fe^{3+} + e^{-}$
  3. Reduction: $4e^-+ 14H^+ + Cr _2O _7^{2-} \rightarrow Cr^{3+} + 7H _2O $

    Oxidation: $ \\ Fe^{2+} \rightarrow Fe^{3+} + e^{-}$
  4. Oxidation: $6e^-+ 14H^+ + Cr _2O _7^{2-} \rightarrow Cr^{3+} + 6H _2O $

    Reduction: $ \\ Fe^{2+} \rightarrow Fe^{3+} + e^{-}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given Redox reaction is

$Cr _2O _7^{2-}+Fe^{+2} \longrightarrow Cr^{+3}+Fe^ {3+}$
Oxidation half reaction:- $Fe^{+2} \longrightarrow Fe^{+3}+e^-$
                                          [as oxidation number increases from $2$ to $3$]
Reduction half reaction:- $Cr _2O _7^{2-}+6e^-+14H^+ \longrightarrow 2Cr^{+3}+7H _2O$
                                          [as oxidation number decreases from $6$ to $3$]

Multiple choice redox and stoichiometry applications of redox reaction oxidation- reduction reactions redox reactions chemistry

Two half reactions are given as follows:
$2e^{-} + H^{+} + H _5IO _6 \rightarrow IO^{3-} + 3H _2O $
$Cr \rightarrow Cr^{3+} + 3e^{-}$
Final balanced reaction is:

  1. $3H^{+} + 3H _5IO _6 + 2Cr \rightarrow 2Cr^{3+} + 3IO^{3-} + 9H _2O$
  2. $5H^{+} + 3H _5IO _6 + 2Cr \rightarrow 2Cr^{3+} + 3IO^{3-} + 10H _2O$
  3. $3H^{+} + 3H _5IO _6 + 4Cr \rightarrow 4Cr^{3+} + 3IO^{3-} + 9H _2O$
  4. $3H^{+} + 3H _5IO _6 + 3Cr \rightarrow 3Cr^{3+} + 3IO^{3-} + 9H _2O$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiply each given half reactions by a number to balance electrons on both sides.

$[2e^-+H^++H _5IO _6 \longrightarrow IO^{-3}+3H _2O] \times 3 \longrightarrow (1)$
$[Cr \longrightarrow Cr^{+3}+3e^- ] \times 2 \longrightarrow (2)$
Now adding equation (1) and (2) we get balanced equation
$3H^++3H _5IO _6+2Cr \longrightarrow 2Cr^{+3}+3IO^{3-}+9H _2O$ .

Multiple choice redox and stoichiometry applications of redox reaction oxidation- reduction reactions redox reactions chemistry

In alkaline medium, $ClO _2$ oxidizes $H _2O _2$ to $O _2$ and is itself reduced to ${ClO} _2^{\displaystyle-}$. Number of moles of $H _2O _2$ oxidized by 1 mole of $ClO _2$ is :

  1. 1

  2. 1.5

  3. 0.5

  4. 3.5
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The balanced reaction is as follows:
$H _2O _2 + 2 ClO _2 \rightarrow 2ClO _2^ + O _2 + 2 H^{+}$
So, number of moles of $H _2O _2$ oxidized by 1 mole of $ClO _2$ is 0.5.

Multiple choice redox and stoichiometry applications of redox reaction oxidation- reduction reactions redox reactions chemistry

For the reaction of $MnO _2\,+\,C _2O _{4}^{2-}\,+\,H^+\,\rightarrow\,Mn^{2+}\,+\,CO _2\,+\,H _2O$ the correct whole number stoichiometric coefficients of $MnO _4$ , $C _2$$O _4$ and $H^+$ are respectively :

  1. 2 , 5 , 16

  2. 16 , 5 , 2

  3. 5 , 16 , 2

  4. 2 , 16 , 5
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Balance redox half-reactions: MnO4- + 8H+ + 5e- → Mn^2+ + 4H2O (reduction, gain 5e-); C2O4^2- → 2CO2 + 2e- (oxidation, lose 2e-). LCM of 5 and 2 is 10, so 2 MnO4- (gains 10e-) and 5 C2O4^2- (loses 10e-). H+ balance requires 16 H+ for 2 MnO4-.

Multiple choice chemistry amines chemical reactions of diazonium salts chemical properties of diazonium salts diazonium salts

Sandmeyer reaction is better than Gattermann reaction because:

  1. sandmeyer reaction uses salt of copper while Gattermann reaction uses copper powder.

  2. only one salt is produced in Sandmeyer reaction while Gattermann reaction produces two salts.

  3. sandmeyer reaction gives better yield than Gattermann reaction.

  4. all of the above.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sandmeyer gives a higher yield.So,it is better than Gattermann reaction.

Multiple choice chemistry amines chemical reactions of diazonium salts chemical properties of diazonium salts diazonium salts

Which of the reaction would you choose for the most beneficial conversion shown below?
$ArN _2^+X \rightarrow ArCl$

  1. Sandmeyer Reaction

  2. Gattermann Reaction
  3. Directly reacting with $HCl$

  4. Both A and B
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sandmeyer and Gattermann reactions are two processes used mostly for the above conversion.But Sandmeyer is more beneficial as it gives a higher yield.

Multiple choice chemistry amines chemical reactions of diazonium salts chemical properties of diazonium salts diazonium salts

3- Amino-2, 3-dimethyl butan-2-ol when treated with $ NaNO _{2}/HCl$ gives product (X). (X) on treatment with $LiAlH _{4}$ forms (Y). (Y) on heating with $conc. H _{2}SO _{4}$ forms (Z). The molecular weight of (Z) is :

  1. 81

  2. 82

  3. 83

  4. 84
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

3- Amino-2, 3-dimethyl butan-2-ol is diazotized with sodium nitrite in presence of HCl at low temperature to obtain 3,3-dimethylbutan-2-one (compound X).
The carbonyl group is then reduced to obtain 3,3-dimethylbutan-2-ol (compound Y). This is followed by dehydration to obtain 2,3-dimethylbut-2-ene (compound Z).

Multiple choice action of alkalis on some metals and metal oxides analytical chemistry properties of acids and bases acids, bases and salts chemistry

Which of the following equation represents action of alkali on oxide?

  1. $ZnO+2NaOH\rightarrow Na _2ZnO _2+H _2O$
  2. $Zn\begin{pmatrix}OH\end{pmatrix} _2+2NaOH\rightarrow NaZnO _2+2H _2O$
  3. $PbO+2NaOH\rightarrow Na _2PbO _2+2H _2O$

  4. Both A and C
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Oxides of certain metals react with acid and alkali to give salt and water.
$ZnO+2NaOH\rightarrow Na _2ZnO _2+H _2O$ is the only correct equation.