NEET chemistry

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Question
CBSEENCH11008479

The compressibility of a gas is less than unity at STP, therefore,

  • Vm > 22.4 L

  • Vm < 22.4 L

  • Vm = 22.4

  • Vm = 44.8 L

Solution

B.

Vm < 22.4 L

compressibility (Z) = PVnRTZ less than unity, thereforePVnRT <1or PV<nRT [At STP, P =1 atm, T = 273K, R =0.0821 L atm K-1]i.e or  1 atm x V < 1 x 0.0821 x 273or V <22.4 litres.

Sponsor Area

Question
CBSEENCH11008480

Among the following set of quantum numbers, the impossible set is

  • n l m s
    3 2 -3 -1/2
  • n l m s
    4 0 0 1/2
  • n l m s
    5 3 0 -1/2
  • n l m s
    3 2 -2 1/2

Solution

A.

n l m s
3 2 -3 -1/2

Principal quantum number = n
Azimuthal quantum number = l = 0 to (n-1)
Magnetic quantum number = m = -l to +1
Spin quantum number = s = +1/2 or -1/2
Now,

(i) In first option the given values are,

n=3; l=2; m=-3; s=-1/2

So according to Azimuthal quantum number

l = 0 to (n-1) = 0 to 2 = here it is 2 which is permissible

m = -l to +l = -2 to +2 = here it is 3 which is  not permissible

s = +1/2 or -1/2 = here it is -1/2 whch is permissible

(ii) In the second option given values are,

n = 4; l = 0, m = 0; s= 1/2

So according to Azimuthal quantum number

l = 0 to (n-1) = 0 to 3 = here it is 0 which is permissible

m =-l to +l = -3  to +3 = here it is 0 which is permissible

s = +1/2 or -1/2 = here it is 1/2 whch is permissible

(iii) In the third option given values are,

n =5; l = 3; m= 0; s= -1/2

So according to Azimuthal quantum number

l = 0 to (n-1) = 0 to 4 = here it is 3 which is permissible

m = -l to +l = -4 to +4 = here it is 0 which is permissible

s = +1/2 or -1/2 = here it is -1/2 whch is permissible

(iv) it the forth option given values are,

n=3; l =2; m=-2; s = 1/2

So according to Azimuthal quantum number

l = 0 to (n-1) = 0 to 2 = here it is 2 which is permissible

m = -l to +l = -2 to +2 = here it is 2 which is permissible

s = +1/2 or -1/2 = here it is -1/2 whch is permissible

Question
CBSEENCH11008481

Which of the following is least soluble in water?

  • C2H6

  • CH3OH

  • CH3NH2

  • C6H5OH

Solution

A.

C2H6

C2H6 is non-polar compound and other compounds are polar in nature. Hence, it is least soluble in water.

Question
CBSEENCH11008483

Among the following compounds, which compound is polar as well as exhibit sp2-hybridisation by the central atom.

  • H2CO3

  • SiF4

  • BF4

  • HClO3

Solution

A.

H2CO3

SiF4 and HClO3 have sp3 - hybridisation.

BF3 and H2CO3 have sp2 - hybridisation but BF3 is non-polar.

Therefore, the Correct answer is H2CO3 

Question
CBSEENCH11008484

The energy released when 6 moles of octane is burnt in air will be [Given, ΔHf for CO2 (g). H2O(g) and C8H18 (l), respectively are -490, -240 and +160J/mol]

  • -37.4 kJ

  • -20 kJ

  • -6.2 kJ

  • -35.5 kJ

Solution

D.

-35.5 kJ

C +O2   CO2; G = - 490 J ...(i)H2 + 12O2    H2O ; H =- 240 J ...(ii)8C + 9H2   C8H18; H = +160 J .... (iii)

On applying, 8 x Eq. (i)  + 9x Eq. (ii) -Eq. (iii), we get

C8H18 + 252O2   8CO2  + 9H2OHR0 = [8 x (-490)] + [9 x (-240)] + 160 = -5920 J mol-1

Hence, energy exchange when 6 moles of octane is burnt in air = - 5920 x 6 = -35520 J = -35.5 kJ