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 chemistry substances in common use salts and their properties study of some important salts salts used in daily life

Reaction, $Cl _2 + 2NaOH \rightarrow P$            

What are the products?

  1. $NaCl + NaOCl + H _2$
  2. $NaCl + NaOCl + H _2O _2$
  3. $NaCl + NaOCl + H _2O$
  4. $NaCl + NaOCl + O _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The reaction of non-metals with bases is complex. Example: When chlorine reacts with a base like sodium hydroxide, it gives multiple products like sodium hypochlorite, sodium chloride and water.

$Cl _2 + 2NaOH \rightarrow NaCl + NaOCl + H _2O$

Multiple choice zoology environmental pollution primary air pollutants air pollution - types and sources not for breathing not for drinking

Read the following statements regarding the PAN (peroxyacyl nitrates) and select the correct ones.
(i) It is a secondary pollutant present in photochemical smog.
(ii) It is produced by photochemical reactions between hydrocarbons and nitrogen oxides in the presence of sunlight of UV radiations.
(iii) It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas. 
(iv) It is a lachrymatory substance, causing irritation of eyes.

  1. (i) and (ii)`

  2. (iii) and (iv)

  3. (i), (ii), and (iii)

  4. (i), (ii), (iii) and (iv)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Secondary pollutants are pollutants which form in the atmosphere. These pollutants are not emitted directly from a source (like vehicles or power plants). Instead, they form as a result of the pollutants emitted from these sources reacting with molecules in the atmosphere. Secondary pollutants are concerning as they can be formed from many different compounds. Photochemical smog is made up of various secondary pollutants like ozone, peroxyacyl nitrates (PANs), and nitric acid.

A hazy condition of the atmosphere caused by the reaction of hydrocarbons with molecules of nitrogen oxide in sunlight, which produces complex organic molecules of peroxyacetyl nitrates (PAN). In humid conditions these molecules produce smog. Such phenomena are common in large urban areas (e.g. the Los Angeles basin and Athens) where there are stable atmospheric conditions and a high level of hydrocarbon input from incomplete combustion in car engines. Natural photochemical reactions occur in the high atmosphere with the absorption of radiation by oxygen to produce ozone. 
Peroxyacetyl nitrate (PAN; CH3C(O)OONO2) is an important constituent of photochemical smog. It is also a ubiquitous chemical present throughout the global troposphere. PAN is thermally unstable, however, and decomposes at higher temperatures to reform peroxyacetyl radicals and NO2, that is, the reverse of reaction.
Peroxyacyl nitrates (also known as Acyl peroxy nitrates, APN or PANs) are powerful respiratory and eye irritants present in photochemical smog. They are lachrymators, causing eye irritation at concentrations of only a few parts per billion. At higher concentrations they cause extensive damage to vegetation.
So the correct option is '(i), (ii), (iii) and (iv)'.

Multiple choice bio-chemistry biological oxidation classical idea of redox reactions oxidation reduction redox reaction

Which of the following is a redox reaction?

  1. $C{ a }CO _{ 3 }\quad \rightarrow \quad { { C }{ a }O+{ CO } _{ 2 } }$
  2. $H _{ 2 }+Cl _{ 2 }\quad \rightarrow \quad 2HCl$
  3. ${ C }{ a }O+2HCl\quad \rightarrow \quad { C }{ a }{ Cl } _{ 2 }+{ H } _{ 2 }O$
  4. ${ N }{ a }OH+HCl\quad \rightarrow \quad { N }{ a }{ Cl }+{ H } _{ 2 }O$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A redox reaction involves the change in oxidation states of atoms. In option B, elemental hydrogen and chlorine react to form hydrogen chloride, where hydrogen is oxidized from 0 to +1 and chlorine is reduced from 0 to -1. The other options represent thermal decomposition or double displacement reactions without changes in oxidation numbers.

Multiple choice bio-chemistry biological oxidation classical idea of redox reactions oxidation reduction redox reaction

Which reaction is not a redox reaction?

  1. $Mg+2HNO _3\rightarrow Mg(NO _3) _2+H _2$
  2. $2Mg(NO _3) _2\rightarrow 2MgO+4NO _2+O _2$
  3. $SO _2+NO _2\rightarrow SO _3+NO$
  4. $SO _3+H _2O\rightarrow H _2SO _4$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A redox reaction is characterized by a change in the oxidation states of the reacting species. Option D is a combination reaction between sulfur trioxide and water to form sulfuric acid, where sulfur remains in the +6 oxidation state, oxygen remains in the -2 state, and hydrogen remains in the +1 state throughout. The other three options involve changes in oxidation states, making them redox processes.

Multiple choice bio-chemistry biological oxidation classical idea of redox reactions oxidation reduction redox reaction

$HOCl(aq)$ is the molecule that kills bacteria wen chlorine is added to water. 
The following reaction produces this molecule
${Cl} _{2}(g)+{H} _{2}O(l)\rightleftharpoons HOCl(aq)+{H}^{+}(aq)+{Cl}^{-}(aq)$
Which statement about this reaction is correct?

  1. Chlorine is both oxidised and reduced

  2. Chlorine is oxidised but not reduced

  3. Hydrogen is both oxidised and reduced

  4. Hydrogen is oxidised but not reduced
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Oxidation and reduction are two types of chemical reactions that often work together. Oxidation and reduction reactions involve an exchange of electrons between reactants.

  • Reduction and oxidation occur simultaneously in a type of chemical reaction called a reduction-oxidation or redox reaction.
  • Oxidation Involves Loss of electrons
  • Reduction Involves Gain of electrons.
As we can see the above case with the chlorine .
hence chlorine is both oxidised and reduced

Multiple choice bio-chemistry biological oxidation classical idea of redox reactions oxidation reduction redox reaction

Which of the following reaction is non-redox?

  1. $2NaNO _{3}\rightarrow 2NaNO _{2}+O _{2}$
  2. $CaO+SiO _{2}\rightarrow CaSiO _{3}$
  3. $Fe+H _{2}SO _{4}\rightarrow FeSO _{4}+H _{2}$
  4. $4Ag+8CN^{-}+O _{2}+2H _{2}O\rightarrow 4[Ag(CN) _{2}]^{-}+4OH^{-}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In option B, CaO + SiO2 -> CaSiO3, the oxidation states of Ca (+2), O (-2), and Si (+4) remain unchanged. This is an acid-base reaction, not a redox reaction.

Multiple choice bio-chemistry biological oxidation classical idea of redox reactions oxidation reduction redox reaction

Which of the following is a non - redox process ?

  1. $ SO _{4}^{2-}\rightarrow SO _{3} $
  2. $ Cr _{2}O _{7}^{2-}\rightarrow CrO _{4}^{2-} $
  3. $ PO _{4}^{3-}\rightarrow P _{2}O _{7}^{4-} $
  4. $ C _{2}O _{4}^{-2}\rightarrow CO _{2} $
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

In Redox reaction oxidation state changes  


(a) In $ SO _{4}^{-2}, $ Its $ S^{+6} $
In $ SO _{3}, $ Its $ S^{+6}$
$ \therefore$ In $SO _{4}^{-2}\rightarrow SO _{3},$ there is no change 
in oxidation state of $ O^{+5}$
$ \therefore $ Non- redox reaction 

(b) In $ Cr _{2}O _{7}^{-2} $
Lets oxidation state of Cr be x 
$ \therefore 2(x)+7(-2) = -2 $
$ \therefore 2x+(-14) = -2 $
$ \therefore 2x = 12 $
$ \therefore x = 16 $

In $ CrO _{4}^{-2} $ 

Let oxidation Sate of Cr be y
$ y+4(-2) = -2 $
$ y-8 = -2 $
$ y = +6 $
$ \therefore $ oxidation of Cr remain same 
$ \therefore $ Non- redox Readtion

(C) In $ PO _{4}^{-3}, $ Its $ P^{+} $
and In $ P _{2}O _{7}^{-4} $
Let oxidation sate of P be x 
$ 2x+7(-2) = -4 $
$ 2x-14 = -4 $
$ \therefore 2x = 10 $  $ \therefore $ Non - redox Reaction 
$ \therefore x = 5 $

(d) In $ C _{2}O _{4}^{-2},$ Its $ C^{+3}$
In $ Co _{2},$ Its $ C^{+4} $  $ \therefore $ Redox reaction 

Hence, the correct options are $\text{A}$, $\text{B}$ and $\text {C}$

Multiple choice polyhalogen compounds haloalkanes and haloarenes chemistry

Consider the following reaction $C _2H _5I \xrightarrow[x]{\triangle} $ (Pleasant smelling liquid) X is?

  1. Sodium

  2. Dry silver oxide

  3. Ethyl chloride

  4. Dry silver powder
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Since, the product is a pleasent smelling liquid, it must be an ether. $C _2H _5I$ forms diethyl ether on reaction with dry silver oxide.

Hence $X$ is an dry silver oxide.

Multiple choice polyhalogen compounds haloalkanes and haloarenes chemistry

Dehydrohalogenation of alkyl halides is a common preparation method of:

  1. alkenes

  2. alkanes

  3. haloalkenes

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

Dehydrohalogenation is an organic reaction in which alkyl halide when boiled with alcoholic alkali gives corresponding alkene. It is known as elimination reaction.

Multiple choice polyhalogen compounds haloalkanes and haloarenes chemistry

Alkaline hydrolysis of 1,1,1-trichloro derivative (A) of an alkane gives a molecule (B) which produces red coloration with aqueous ${ FeCl } _{ 3 }$. The compound (A) is ?

  1. ${ CH } _{ 3 }{ CH } _{ 2 }{ CCl } _{ 3 }$
  2. ${ CH } _{ 3 }{ CCl } _{ 3 }$
  3. ${ CH }{ Cl } _{ 3 }$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Alkaline hydrolysis of a trichloro derivative will give a carboxylic acid. The carboxylic acid that gives red colouration with aqueous $FeCl _{3}$ is acetic acid $CH _{3}COOH$. Hence, the compound  A is $CH _{3}CCl _{3}$.
Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

When manganese dioxide is treated with HCl, the oxidising agent in the reaction is__________.

  1. $MnO _2$
  2. $HCl$
  3. $H _2O$

  4. The reaction is not a redox reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When Manganese dioxide reacts with $HCl$, it gives chlorine gas, water and $MnCl _2$. $MnO _2$ is the oxidising agent as it oxidises $HCl$ to $Cl _2$ which loses the hydrogen atom.

Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

On reacting $MnO _2$ with $HCl$,
1. $Mn^{4+}$ is reduced to      
2. $Cl^{-}$ is oxidised to

  1. $Mn^{3+}, Cl^{4+}$
  2. $Mn^{2+}, Cl$
  3. $Mn, Cl$
  4. $Mn$ is not reduced nor $Cl$ is oxidised
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Manganese dioxide on reacting with hydrochloric acid, undergoes redox reaction. $MnO _2$ is the oxidising agent while $HCl$ is the reducing agent. $Mn^{4+}$ is thus reduced to $Mn^{2+}$ whereas, $Cl^{-}$ is oxidised to $Cl$.