JEE 2018 :: Chemistry (2018) :: Solved questions (2018)

• Chemistry (2018) - Solved questions (2018)

The ammonia prepared by treating ammonium sulphate with calcium hydroxide is completely used by NiCl₂. 6H₂O to form a stable coordination compound. Assume that both the reactions are 100% complete. If 1584 g of ammonium sulphate and 952 g of NiCl₂ .6H₂O are used in the preparation, the combined weight (in grams)of gypsum and the nickel -ammonia coordination compound thus produced is  ......

(Atomic weights is g mol-1:H=1,N=14, O=16, S=32, Cl=35.5, Ca=40, Ni=59)

Answer:

Explanation:

Balanced equations of reactions used in the problem are follows,

(i)  $(NH_{4})_{2}SO_{4}+Ca(OH)_{2}\rightarrow CaSO_{4}.2H_{2}O+2NH_{3}$

          1 mol (132g)                                        1 mol (172 g)           2 mol (2×17=34g)

(ii)    $Nicl_{2}.6H_{2}O+6NH_{3}\rightarrow [Ni(NH_{3})_{6}]Cl_{2}+6H_{2}O$

              1mol (238g)       6mol (102g)                  1 mol (232 g)

  Now, in Eq .(i)

     If, 1584 g of ammonium sulphate is used.

i.e, 1584 g of (NH₄)₂ SO₄ = $\frac{1584}{132}=12 mol$

So, accordingto the Eq .(i)  given above 12 moles of (NH₄)₂ SO₄ produces 

(a) 12  moles of gypsum

 (b) 24 moles of ammonia

         Here , 12 moles of gypsum= 12×172=2064 g

and   24 moles of NH₃=24 × 17=408 g

 Further , as given in question,

      24 moles of NH₃ produced in reaction (i) is completly utilised by 952 g or 4 moles of NiCl_2. 6H₂O to produce 4 moles of [Ni(NH₃)₆ ]Cl₂.

  So 4 moles of [Ni (NH₃)₆ ]Cl₂ =4× 232 =928 gms

Hence, total mass of gypsum and nickel ammonia coordination compound [Ni(NH₃)]₆Cl₂

                                         =2064+928=2992

A reversible cyclic process for an ideal gas is shown below. Hence , P , V and T are pressure, volume and temperature respectively , The thermodynamic parameters q,w, H and U are heat, work, enthalpy and internal energy, respectively.

The correct options is (are)

Answer:

Explanation:

In the given curve AC represents isochoric process as volume at both the points is same i.e., V₁

Similarly , AB represents isothermal process ( as both the points are at T₁ temperature )  and BC represents  isobaric process as both the points are at p₂ pressure.

       Now (i) for option (a)

                          $q_{AC}=\triangle U_{BC}=nC_{v}(T_{2}-T_{1})$

where, n= number of moles,

     C_v= specific heat capacity at constant volume

   However, W_AB ≠ P₂ ( V₂ -V₁) instead 

            $w_{AB}=nRT_{1}ln(\frac{V_{2}}{V_{1}})$

   So, this option is incorrect.

(ii) For option (b)

           $q_{BC}=\triangle H_{AC}=nC_{p}(T_{2}-T_{1})$

   where , C_p= specific heat capacity at constant  pressure.

Likewise,

     $w_{BC}=-P_{2}(V_{1}-V_{2})$

Hence, the option is correct.

(iii)  For option (c)

        as $nC_{p}(T_{2}-T_{1})<nC_{v}(T_{2}-T_{1})$

So         $\triangle H_{CA}<\triangle U_{CA}$

 and    $q_{AC}=\triangle U_{BC}$

Hence, this option is also correct.

(IV)   For option (d)

         Although    $q_{BC}=\triangle H_{AC}$

    but  $\triangle H_{CA}>\triangle U_{CA}$

  Hence, this option is incorrect.

Based on the compounds of group 15 elements, the correct statement(s) is (are)

Answer:

Explanation:

Statement wise  explanation is

(i) Statement (a)  Bi₂O₅  is metallic oxide while N₂O₅ is a non-metallic oxide.

           Metallic oxides being ionic are basic in nature while non metallic oxides being covalent are acidic in nature. This confirms more basic nature of Bi₂O₅ in comparison to N₂O₅ .Hence this is correct statement.

(ii) Statement (b)  The electronegativity difference between N(3) and F(4) is less as compared to the electronegativity difference between Bi(1.7) and F(4). More electronegativity difference leads to ionic compounds. Thus, NF₃  must be more covalent in nature as compared to BiF₃ .Hence, this statement is also correct.

(iii) Statement (c) In NH₃ intermolecular hydrogen bonding is present, which is altogether absent in PH₃ .Thus , PH₃ boils at lower temperature than NH₃. Hence, this is also a correct statement.

(IV) Statement (d)  Due to smaller size of N the lone pair-lone pair repulsion is  more in N-N single bond as compared to P-P single bond. This results to weaker N-N single bond as compared to P-P single bond. Hence, this statement is incorrect.

The correct statement(s) regarding the binary transition metal carbonyl compounds is (are)  [Atomic numbers :  Fe=26, Ni= 28]

Answer:

Explanation:

(i)  Statement (a) The total number of valence shell electrons at metal centre in Fe (CO)₅  or Ni(CO)₄ is  8 instead of 16 as shown below.

Hence, this statement is incorrect

(ii) Statement (b) Carbonyl complexes are predominantly low spin complexes due to strong ligand fields. Hence, this statement is correct

(iii) Statement (c) For central metal lowering of oxidation state results to increase in electron density on it. This in turn results to increase in the extent of synergic bonding. Thus, we can say "metal carbonyl bond strengthens when oxidation state of the metal is lowered".

 Hence, it is a correct statement.

(IV) Statement (d) Increase in positive charge on metal (i.e., increase in oxidation state) results to decrease in synergic bonding strength.

   This, in turn, makes the C-O bond stronger instead of weaker. Hence this statement is also incorrect.

Consider the following reaction and statments

$[Co(NH_{3})_{4}Br_{2}]^{+}+Br^{-}\rightarrow [Co(NH_{3})_{3}Br_{3}]+NH_{3}$

I. Two isomers are produces if the reactant complex ion is a cis-isomer.

II.Two isomers are produced if the reactant complex ion is a trans- isomer.

III.  Only one isomer is produced if the reactant complex ion is a trans-isomer.

IV. Only one isomer is produced if the reactant complex ion is a cis-isomer

 The correct statements are

Answer:

Explanation:

If the reactant is cis isomer than following reaction takes place.

i.e. two isomers are produced. If the reactant is trans  isomer than following reaction takes place.

i.e only 1 isomer is produced .Thus, statement  (I) and (III) are correct  resulting to option (b) as the correct answer.

• Chemistry (2018) - Solved questions (2018)