West Bengal Joint Entrance Examination Board conducts the WBJEE exam for admission to engineering and pharmacy courses in different colleges in the state of West Bengal. WBJEE 2017 Chemistry paper solutions are given on this page. BYJU’S provides accurate solutions that are prepared by subject experts. These solutions will help students to get an idea about the difficulty level and question pattern of the WBJEE exam. Students can download the PDF format for free to practise the paper offline.
Question 1: For same mass of two different ideal gases of molecular weights M1 and M2, plots of log V vs log P at a given constant temperature are shown. Identify the correct option
Solution:
Answer: (a)
Ideal gas equation PV = nRT ….(1)
Mole(x) = wt/Mw = W/M
So we can write from eq. (1) PV = (W/M) RT …..(2)
Since here w, R and T -> constant
So let w RT = k (new constant)
Now from equation (2) we get
PV = K/M ….(3)
Taking log of both side log (PV) = log (K/M)
⇒ log P + log V = log (K/M)
⇒ log V = –log P + log (K/M) …..(4) [y = mx + c]
Here + log (K/M) -> intercept
Now we can write the intercept for ideal gas (1) and (2) by the help of equation (1)
Ideal gas having M1 molar weight -> intercept = log (K/M1)
Ideal gas having M2 mw -> intercept = + log (K/M2)
From the graph we see, log (K/M2)>log(K/M1)
⇒ K/M2>K/M1
⇒ M1 > M2
Hence correct option is (a).
Question 2: Which of the following has the dimension of ML0T–2 ?
Solution:
Answer: (b)
Surface tension = Work done per unit area
= dw/dA = F.dx/dA…..(1) {since dw = fdx}
dx -> distance /length -> m
dA -> Area -> m2
Since F = Ma = kg m/sec2….(2)
Eq. (2) -> Eq. (1)
Surface tension = (kg m/sec2) × m/m2 = kg sec–2
Therefore the dimension of the surface tension is
[M1L0T–2]
Hence correct option (b).
Question 3: If the given four electronic configurations
(i) n = 4, l = 1 (ii) n = 4, l = 0 (iii) n = 3, l = 2 (iv) n = 3, l = 1
are arranged in order of increasing energy, then the order will be
Solution:
Answer: (a)
According n + l rule, n + l value increases, energy of orbital also increases
Hence (1) n + l = 4 + 1 = (5) ⇒ 4p orbital
(2) n + l = 4 + 0 = (4) ⇒ 4s orbital
(3) n + l = 3 + 2 = (5) ⇒ 3d orbital
(4) n + l = 3 + 1 = (4) ⇒ 3p orbital
If for any two cases n + l values are equal, then whose orbital which have lower n value, their orbital energy also lower.
Hence overall order of energy = 1 > 3 > 2 > 4
So correct option is (a).
Question 4: Which of the following sets of quantum numbers represents the 19th electron of Cr (Z = 24)?
Solution:
Answer: (b)
Electronic configuration of Cr (Atomic number 24)
Here 19e- enter in 4s orbital because 4s orbital have lower energy compared to 3d orbital
Hence correct option is (b).
Question 5: 0.126 g of an acid is needed to completely neutralize 20 ml 0.1 (N) NaOH solution. The equivalent weight of the acid is
Solution:
Answer: (d)
Number of eq. of acid = No. of eq. of base
= N × V/1000 = 0.1 × 20/1000 = 2 × 10–3
N = No. of eq. of solute /V(litre)
⇒2×10–3 equivalents have mass = 0.126 g
Hence, mass of 1 equivalent = 0.126/2 ×10-3 = 63 g
So correct option is (d).
Question 6: In a flask, the weight ratio of CH4 (g) and SO2(g) at 298 K and 1 bar is 1 : 2. The ratio of the number of molecules of SO2(g) and CH4(g) is
Solution:
Answer: (c)
Wt. ratio WCH4 : WSO2 = 1:2
Moles (n) = wt/Mw
Mw of SO2 = 64 g mol-1
Mw of CH4 = 16 g mol-1
nSO2/nCH4 = (WSO2 ×MCH4 )/ (MSO2 ×WCH4 )
So mole ratio of SO2: CH4 = 1 : 2
Hence correct option is c.
Question 7: C6H5F18 is a F18 radio-isotope labeled organic compound. F18 decays by positron emission. The product resulting on decay is :
Solution:
Answer: (a)
Positron emission by 9F18 follows as
9F18 -> 8O18 + +1e0
When an element emit a positron [Beta particle (β+)] decreases the no. of proton by one. and increases the neutron by one. While mass number A remains the same.
So resulting product is as ⇒ C6 H6 O18
Hence correct option is (a).
Question 8: Dissolving NaCN in de-ionized water will result in a solution having
Solution:
Answer: (d)
On dissolving NaCN
NaCN + H2O -> NaOH (strong base) +HCN ->Weak acid
Hence pH > 7
So correct option is (d).
Question 9: Among Me3N, C5H5N and MeCN (Me = methyl group) the electronegativity of N is in the order
Solution:
Answer: (a)
As the % S increases electronegativity increases.
Hence order of E.N. MeCN > C5H5N > Me3N
So correct option is (a).
Question 10: The shape of XeF5– will be
Solution:
Answer: (c)
Shape of XeF5-:
No. of electron pair = (8+5+1)/2 = 7 -> sp3d3 hybridisation
⇒ np +l p = 7
l p = 7–5 = 2
⇒ l p = 2
Shape of molecule which have sp3d3 hybridisation and 2lp
⇒ l p present at axial to minimize the repulsion
⇒ Hence shape is planar & geometry pentagonal bipyramidal
Geometry -> Pentagonal bipyramidal
Shape -> planar
Question 11: The ground state magnetic property of B2 and C2 molecules will be
Solution:
Answer: (a)
MOT diagram of C2 molecule ⇒ 6C -> 1s22s22p2
Unpaired electron = 0
MM = 0 BM
No. of unpaired electron = 2
MM = √(n(n+2) = √(2(2+2) = √8
M.M = 2.83 BM
Hence C2 diamagnetic & B2 paramagnetic
So correct option is (a).
Question 12: The number of unpaired electrons in [NiCl4]2–, Ni(CO)4 and [Cu(NH3)4]2+ respectively are
Solution:
Answer: (b)
(1)[NiCl4]2– -> Ni+2 -> 3d8
Since Cl- is a weak ligand, so there is no pairing of electrons
No. of unpaired electron = 2
Since Co is a strong ligand, so there is pairing of electrons occurs
No. of unpaired electrons = 0
No. of unpaired electrons = 1
Hence correct option is (b).
Question 13: Which of the following atoms should have the highest 1st electron affinity?
Solution:
Answer: (a)
Electro affinity ⇒ E.A. of an atom is defined as the amount of energy released when an electron is attached to a neutral atom or molecule in the gaseous state to form a negative ion.
x(g) + e- -> xg- + energy
E.A. of “F” is 2nd highest amongst periodic table after “Cl”
Question 14: PbCl2 is insoluble in cold water. Addition of HCl increases its solubility due to
Solution:
Answer: (a)
Solubility of PbCl2 increases in cold water on the addition of HCl due to the formation of soluble complex like [PtCl3]- (aq.).
PbCl2 react with HCl as follows
PbCl2(s) + Cl- -> [PbCl3]- (aq)
PbCl2(s) + 2Cl- -> [PbCl4]2– (aq)
Thus the addition of excess amount of Cl- ions change the PbCl2 as soluble complex of [PbCl4]2-.
Hence solubility increases .
Question 15: Of the following compounds, which one is the strongest Bronsted acid in aqueous solution?
Solution:
Answer: (a)
As the oxidation state of Central atom increases Electron negativity increases and acidity increases.
I effect increases, acidity increases
Hence correct option is (a).
Question 16: The correct basicity order of the following lanthanide ions is
Solution:
Answer: (d)
Due to the lanthanoid contraction, increase in atomic number the basicity decrease from La3+ to Lu3+.
So correct order of basicity follow as La3+ > Ce3+ > Eu3+ > Lu3+.
Hence correct option is (d).
Question 17: When BaCl2 is added to an aqueous salt solution, a white precipitate is obtained. The anion among CO32– , SO32– and SO42– that was present in the solution can be :
Solution:
Answer: (d)
Reaction of BaCl2 with CO32– , SO32– & SO42– follow as
Hence correct option is (d).
Question 18: In the IUPAC system, PhCH2CH2CO2H is named as
Solution:
Answer: (a)
Hence correct option (a).
Question 19: The isomerisation of 1-butyne to 2-butyne can be achieved by treatment with
Solution:
Answer: (d)
Isomerisation of 1-butyne to 2-butyne can be achived by treatment with ethanolic KOH.
Question 20: The correct order of acid strengths of benzoic acid (X), peroxybenzoic acid (Y) and p-nitrobenzoic acid (Z) is
Solution:
Answer: (c)
[Most acidic due to –R & –I effect of –NO2 group]
Acidity ∝ -R>-H>-I
Hence correct order of acidity is 3 > 1 > 2
So correct option is (c)
Question 21: The yield of acetanilide in the reaction (100% conversion) of 2 moles of aniline with 1 mole of acetic anhydride is
Solution:
Answer: (b)
The reaction of 2 moles with 1 mole of acetic anhydride follows as
Wt. of acetanilide = moles × Mw = 1 × 135
= 135 g
Hence correct option is (b).
Question 22: The structure of the product P of the following reaction is
Solution:
Answer: (c)
Reaction mechanism follows as
Question 23: ADP and ATP differ in the number of
Solution:
Answer: (a)
ADP ⇒ Adenosine diphosphate ⇒ 2 phosphate group
ADP ⇒ Adenosine Triphosphate ⇒ 3 phosphate group
⇒ So difference only one phosphate group
Hence correct option is (a).
Question 24: The compound that would produce a nauseating smell/odour with a hot mixture of chloroform and ethanolic potassium hydroxide is
Solution:
Answer: (c)
Carbyl – amine reaction
When CHCl3 + KOH (alcoholic), React with 10 amine
Or aromatic amine: Isocyanide product will form, reaction follow as –
Hence correct option is (c).
Question 25: For the reaction below
the structure of the product Q is:
Solution:
Answer: (b)
Reaction mechanism follow as :
Question 26: You are supplied with 500 ml each of 2N HCl and 5N HCl. What is the maximum volume of 3M HCl that you can prepare using only these two solutions?
Solution:
Answer: (c)
We have to prepare maximum volume solution of 3N. {3 M is same as 3 N for HCl due to valency factor = 1}
Hence we take 500 ml of 2N solution & x ml of 5N solution
N1V1 + N2V2 = N3V3
⇒500 × 2 + x × 5 = 3 (x + 500)
1000+5x = 3x+1500
x = 250 ml
Hence final volume of the solution = x + 500 = 250 + 500 = 750 ml
Question 27: Which one of the following corresponds to a photon of highest energy?
Solution:
Answer: (a)
Energy of photon (E) = h ν = hc/λ
(1) E = hc/λ = (6.626 ×10-34J S×3×108m sec-1)/300×10-9m
E = 6.626 ×10-19J
(2) E = h ν =6.626 ×10–34 J. sec × 3 × 108 sec–1
E = 1.9878 ×10-25J
(3) E = chν = 6.626 × 10–34 J sec×30×102 m–1×3 ×108 m sec–1
= 5.9634 ×10–22 J
(4) E = 6.626 × 10–27 J
Among these, maximum energy = 6.626×10–19 J
Hence correct option is (A)
*v is representing "nu" here.
Question 28: Assuming the compounds to be completely dissociated in aqueous solution, identify the pair of the solutions that can be expected to be isotonic at the same temperature :
Solution:
Answer: (c)
For isotonic at some temperature π1 = π2
i1c1RT = l2c2RT …..(1)
Option (c) 0.03 M NaCl & 0.02 M MgCl2
Now from equation (1)
2 × 0.03 = 0.06
3× 0.02 = 0.06
So i1c1 = i2c2.
Hence it is isotonic.
Question 29: How many faradays are required to reduce 1 mol of Cr2O72– to Cr3+ in acid medium?
Solution:
Answer: (d)
Hence reduction of 1 mol required 6 electron
So no. of the Faraday’s = 6F
Question 30: Equilibrium constants for the following reactions at 1200 K are given :
2H2O(g) ⇌ 2H2(g) + O2(g) ; K1 = 6.4 × 10–8
2CO2(g) ⇌ 2CO(g) + O2(g); K2 = 1.6 × 10–6
The equilibrium constant for the reaction
H2(g) + CO2(g) ⇌ CO(g) + H2O(g) at 1200 K will be
Solution:
Answer: (d)
K3 = 5
Hence correct option is (d).
Question 31: In a close-packed body-centred cubic lattice of potassium, the correct relation between the atomic radius (r) of potassium and the edge-length (a) of the cube is
Solution:
Answer: (d)
Here, we have √3a = 4r
r = √3a/4
(Where a = edge length, r = radius of lattice sphere)
Question 32: Which of the following solutions will turn violet when a drop of lime juice is added to it?
Solution:
Answer: (b)
Lime Juice is acidic in nature as it contains “citric acid”. The citric acid present in lime juice will liberate I2 from the iodide which will give purple or violet colour.
Reaction follow as
Question 33: The reaction sequence given below gives product R
The structure of the product R is
Solution:
Answer: (d)
Reaction mechanism of the reaction follows as
This reaction is an example of “Borodine” Huns Diecker reaction.
Question 34: Reduction of the lactol S
with sodium borohydride gives
Solution:
Answer: (c)
The reduction reaction of lactol (s) with sodium borohydride (NaBH4)
Hence correct option is (c).
Question 35: What will be the normality of the salt solution obtained by neutralizing x ml y (N) HCl with y ml x (N) NaOH, and finally adding (x + y) ml distilled water?
Solution:
Answer: (b)
Normality = wt × 1000/eq.wt ×v(ml) = No. of M.eq/volume of solution (ml)
Reaction between NaOH & HCl follow as
It is an acid-base reaction hence final product is salt & H2O
Question 36: During electrolysis of molten NaCl, some water was added. What will happen?
Solution:
Answer: (b,c,d)
Electrolysis of molten NaCl
Molten NaCl (An electrolyte) means free Na+ ions & Cl- ion, so it is conducts current with the help of ions. As electric current is passed in the cell, Cl- ions are attracted to the anode (positive) & Na+ ions attracted to cathode (negative).
Anode to cathode follow as :
Cathode Na+ + e- -> Na(a)
Anode Cl- -> ½ Cl2 + e-
Overall reaction Na+ +Cl- -> Na + ½ Cl2
If we add some water then, H2 will liberate & NaOH will form in the solution and reaction follows as
Exothermic reaction
Na(s) + H2O -> NaOH + (1/2)H2 +Q (energy)
Hence correct option is (b,c,d).
Question 37: The role of fluorspar, which is added in small quantities in the electrolysis reduction of alumina dissolved in fused cryolite, is
Solution:
Answer: (b,c)
The electrolysis of Al2O3 is carried out in the steel tank linked inside with graphite. The graphite lining serves as cathode. The anode is also made of graphite rods hanging in the molten mass the electrolyte consist of alumina dissolved in fused cryolite (Na3AlF6) & CaF2. Cryolite lower the melting point of alumina to 950°C and CaF2 increase the fluidity of the mass, so that the liberated aluminium metal may sink at the bottom of the cell. Therefore, it makes the fused mixture very conducting & lower the fusion temperature of the metal. When an electric current is passed through this mixture the Al is collected at the cathode in the molten state & sinks at the bottom & it is tapped off.
Hence correct option is (b,c).
Question 38:The reduction of benzenediazonium chloride to phenyl hydrazine can be accomplished by
Solution:
Answer: (a,b)
Reaction diazonium salt with following reagent follow as :
Hence correct option are (a,b)
Question 39: The major product(s) obtained from the following reaction of 1 mole of hexadeuterobenzene is/are
Solution:
Answer: (a)
Hence correct option is (a).
Question 40: Identify the correct statement(s) :
The findings from the Bohr model for H-atom are
Solution:
Answer: (a,b,c)
(A) Angular momentum = nh/2π where [n = 1, 2, 3]
(B) rn = 0.529 ×n2/z Å
For H, z = 1
⇒ n = 1 (according question)
r = 0.529Å
(C) En = – 13.6 × z2/n2 eV/atom
En ∝ 1/n2
(D) From the above reaction
E1 = – 13.6 eV/atom
E2 = – 13.6 ×z2/22 = –3.4 eV/atom
E3 = – 13.6/9 = 1.51 ev atom
E2 – E1 = 10.2 ev/atom
E3 –E2 = 0.89 ev /atom
So (E2–E1) > (E3–E2) > (E4–E3) ……
As the difference between the successive energy level decreases, “n” increases.
Hence, correct option is (a,b,c).