Tag: chemistry

Questions Related to 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. ${C} _{2}{H} _{5}MgBr+{SO} _{3}$


Correct Option: B
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.

Which of the following reaction involves copper metal?

  1. Wurtz reaction

  2. Wurtz-Fittig reaction

  3. Ullmann reaction

  4. Frankland reaction


Correct Option: C
Explanation:

Wurtz & Wurtz-Fittig reactions involve Sodium (Na) metal.


Frankland reaction involves Zinc or Magnesium (Zn or Mg) metal.

Ullmann reaction involves Copper (Cu) metal.

Option C is correct.

On reacting with which of the following chemicals sulphur undergoes combination reaction?

  1. metals

  2. nonmetals

  3. acids

  4. alkalies


Correct Option: A,B
Explanation:

 On reacting with metals and non metals sulphur undergoes combination reaction.
$\displaystyle Fe+S \rightarrow FeS$
$\displaystyle Cl _2+2S \rightarrow S _2Cl _2$
Note:
A combination reaction (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product).

The number of equivalents of $Na _{2}S _{2}O _{3}$ required for the volumetric estimation of one equivalent of $Cu^{2+}$ is:

  1. $1/3$

  2. $1$

  3. $3/2$

  4. $2/3$


Correct Option: B
Explanation:

Number of equivalents of reacting species in a chemical reaction are same.

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. $166.67$


Correct Option: D
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 $

A solid $PQ$ has rock salt type structure in which $Q$ atoms are the corners of the unit cell. If the body-centered atoms in all the unit cells are missing, the resulting stoichiometry will be

  1. $PQ$

  2. $P{Q} _{2}$

  3. ${ P } _{ 3 }{ Q } _{ 4 }$

  4. ${ P } _{ 4 }{ Q } _{ 3 }$


Correct Option: C

In a solid $AB$ of $NaCl$ structure, A atoms occupy the corners of the cubic unit cell. If all the corner atoms are removed then the formula of the unit cell will be

  1. $A _{4}B _{4}$

  2. $B$

  3. $A _{3}B _{4}$

  4. $AB$


Correct Option: C

Number of electrons involved in the electrodeposition of 63.5 g of Cu from solution of $ CuSO _{4} $ is:

  1. $ 6.022\times 10^{23} $

  2. $ 3.011\times 10^{23} $

  3. $ 12.044\times 10^{23} $

  4. $ 6.022\times 10^{23} $


Correct Option: C
Explanation:
$ Cu^{2+}+2e^-\rightarrow Cu $ 

1 mole Cu = 63.5 g
 
For deposition of 1 mole of Cu, 2 moles of $e^-$ is required.

$ \therefore$ Number of electrons $ =12.044\times 10^{23} $      
                                    
Hence, option C is correct.

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^{-}$


Correct Option: A
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 $3$]

Which particles are gained and lost during a redox reaction?

  1. Protons

  2. Neutrons

  3. Electrons

  4. Positrons


Correct Option: C
Explanation:

  • Indirect redox reactions only take place if in between the electrodes is an environment that is conducive for electric current (meaning that charged particles are present that can freely move around, like the ions of dissolved or molten salts). There is no direct contact between the particles of the oxidation and the reduction. The transfer of the electrons is realised via-via, mostly via metal wiring or other conductive material. 
Exteriorly the conducting wires take care for the electron transport from RED to OX, without direct contact between the reactants.