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NEET Chemistry Solved Question Paper 2015

Multiple Choice Questions

4.0 g molecular PCl₅ were heated in a vessel of 6 L volume. At equilibrium state , 50% of PCl₅ is dissociated. The equilibrium constant for the reaction is :

0.66 mol L^-1
0.33 mol L^-1
0.44 mol L^-1
0.88 mol L^-1

0.33 mol L^-1

PCl₅ $⇌$ PCl₃ + Cl₂

Moles before

dissociation C 0 0

Moles after

dissociation C(1 - $α$ ) C $α$ C $α$

K_c = $\frac{[{PCl}_{3}] [{Cl}_{2}]}{[{PCl}_{5}]} = \frac{C^{2} α^{2}}{C (1 - α)} = \frac{{Cα}^{2}}{(1 - α)}$

Given , C = $\frac{4}{6}$ and $α$ = 0.5 $[∵ C = \frac{mole}{litre}]$

K_c = $\frac{4 \times (0.5)^{2}}{6 \times (1 - 0.5)} = 0.33 mol L^{- 1}$

One mole of FeC₂O₄ is oxidised by x moles of Cr₂ $O_{7}^{2 -}$ in acidic medium , x is:

0.5

Cr₂ $O_{7}^{2 -}$ + 14H⁺ + 6e^- $\to$ 2Cr³⁺ + 7H₂O

FeC₂O₄ $\to$ Fe³⁺ + 2CO₂ + 3e^- ] x 2

________________________________________

$\underset{1 mole}{{Cr}_{2} O_{7}^{2 -}}$ + $\underset{2 moles}{2 {FeC}_{2} O_{4}}$ + 14H⁺ $\to$ 2Cr³⁺ + 2Fe³⁺ + 4CO₂

+ 7H₂O

Thus, one mole of FeC₂O₄ is oxidised by 0.5 mole of

Cr₂ $O_{7}^{2 -}$ in acidic medium.

The number of $σ$ bonds in P₄O₁₀ is:

The number of $σ$ bonds in P₄O₁₀ is 16. There are also four $π$ bonds presents in P₄O₁₀ molecule.

The decreasing nucleophilicity of the following is:

I. CH₃S^- II. CH₃O^-

III. ^-OH IV. EtO^-

II > III > 1V > I
III > IV > I > II
IV > III > I > II
II < I < IV < III

IV > III > I > II

Acidity is explained as

CH₃SH > CH₃OH > H₂O > EtOH

Basicity : CH₃S^- < CH₃O^- < ^-OH < EtO^-

When nucleophilic centre is different (CH₃S^-and CH₃O^-) and they are from the same group, nucleophilicity is opposite to basicity.

$∴$ Nucleophilicity EtO^- > ^-OH > CH₃S^- > CH₃O^-
Hence, the answer is (c)

For a chemical reaction, temperature is raised from 25° C to 35° C. The value of equilibrium constant, K_p is doubled . The heat of reaction ( $Δ$ H) for the reaction will be :

13.834 kcal
11.714 kcal
10.726 kcal
4.312 kcal

10.726 kcal

Given that , T₁ = 25°C = 298 K
T₁ = 35^°C = 308 K

$\frac{K_{P_{2}}}{K_{P_{1}}}$ = 2R = 2calK^-1mol^-1

From van't Hoff equation ,

2.303log $\frac{K_{P_{2}}}{K_{P_{1}}}$ = $\frac{ΔH}{R} [\frac{T_{2} - T_{1}}{T_{1} T_{2}}]$

2.303 log 2 = $\frac{ΔH}{2} [\frac{308 - 298}{308 \times 298}]$

or , $ΔH$ = 12726 cal = 10.726 kcal

Consider the following pairs of ions:

I. Sc³⁺ and Ti⁴⁺ II. Mn²⁺ and Fe²⁺

III. Fe²⁺ and Co³⁺ IV. Cu⁺ and Zn²⁺

Among these pairs ofions, isoelectronic pairs would include:

II, III and IV
I, III and IV
I, II and IV
I, II and III

I, III and IV

I. Electrons in so³⁺ = 18 and in Ti⁴⁺ = 18
II. Electrons in Mn²⁺ =23 and in Fe²⁺ = 24
III. Electrons in Fe²⁺ = 24 and in Co³⁺ =24
IV. Electrons in Cu⁺ = 28 and in Zn²⁺ = 28

A litre solution containing NH₄Cl and NH₄OH has hydroxide ion concentration of 10^-6mol L^-1. Which of the following hydroxide could be precipitated when the solution is added to 1L solution of 0.1M metal ions?

Ba(OH)₂ (Ksp = 5 x 10^-3)

Ni(OH)₂ (K_sp = 1.6 x 10^-16)

Mn(OH)₂ (K_sp = 2 x 10^-13)

Fe(OH)₂ (K_sp = 8 x 10^-16)

I and IV
III and IV
II and IV
II , III and IV

II and IV

When 1L each solution are mixed

[OH]^- = 10^-6 M (buffer solution)

Mⁿ⁺ = 0.05M

for Q = [0.5][10^-6]² = 5 x 10^-14

Q > K_sp for Fe²⁺ and Ni²⁺

Thus , Fe(OH)₂ and Ni(OH)₂ are precipitate.

Arrange the following (I to IV) in the order of increasing masses:

I. 0.5 mole of O₃

II. 0.5 g atom of oxygen

III. 3.011 x 10²³ mlecules of O₂

IV. 5.6 l of CO₂ at STP

II < IV < III < I
IV < III < I < II
II < I < IV < III
I < II < III < IV

II < IV < III < I

I. 0.5 mole O₃ = 24 g O₃

II. 0.5 g atom of oxygen = 8 g O₂

III. $\frac{3.011 \times 10^{23}}{6.022 \times 10^{23}} \times 32$ = 16 g of O₂

IV. $\frac{5.6}{22.4} \times$ 44 g CO₂ = 11 g CO₂

Forty millilitre of CO was mixed 100 mL of O₂ and the mixture was exploded. On cooling, the reaction mixture was shaken with KOH. What volume of gas is left?

80 ml of O₂
60 ml of O₂
80 ml of CO₂
50 ml of CO₂

80 ml of O₂

$\underset{40 ml}{CO} + \underset{20 ml}{\frac{1}{2} O_{2}} \to \underset{40 ml}{{CO}_{2}} \overset{KOH}{\to} absorbed$

volume of O₂ left = (100-20) = 80 ml

10.

10 moles of ideal gas expand isothermally and reversibly from a pressure of 10 atrn to 1 atm at 300K. What is the largest mass which can lifted through a height of 100 meter?