Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

If a gas expands at constant temperature, it indicates that

  • the kinetic energy of molecules decrease

  • the pressure of the gas increases

  • the kinetic energy of molecules remains the same

  • the kinetic energy of molecules remains the same


C.

the kinetic energy of molecules remains the same

KE space equals space 3 over 2 space RT
KE proportional to space straight T

here, the temperature of the gas remains constant, hence kinetic energy of molecules remains the same.
419 Views

2.

The angular shape of ozone molecule (O3) consists of 

  • 1 sigma and 2 pi bonds

  • 2 sigma and 2 pi bonds

  • 1 sigma and 1 pi bonds

  • 1 sigma and 1 pi bonds


D.

1 sigma and 1 pi bonds

Single bond contains = 1 σ bond
Double bond contains = 1 σ bond + 1 π bond
Triple bond contains = 1σ  bond + 2 π bond

The molecule of O3 is bent with an angle of 116.8o and equal O-O distance of 128 pm. The ozone molecule consists of 2 sigma bond and 1 pi bond.

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3.

If uncertanity in position and momentum are equal, then uncertaninty in velocity is 

  • fraction numerator 1 over denominator 2 straight m end fraction square root of straight h over straight pi end root
  • square root of fraction numerator straight h over denominator 2 straight pi end fraction end root
  • 1 over straight m square root of h over pi end root
  • 1 over straight m square root of h over pi end root

A.

fraction numerator 1 over denominator 2 straight m end fraction square root of straight h over straight pi end root

According to Heisenberg's uncertainty principle, it is impossible to determine simultaneously the position and momentum of moving a particle, ie.
left parenthesis increment straight x right parenthesis space straight x space left parenthesis increment straight p right parenthesis space greater or equal than fraction numerator straight h over denominator 4 straight pi end fraction
Here comma space increment straight x space equals space increment straight p space equals space straight m. increment straight v
increment straight v squared space equals space fraction numerator straight h over denominator straight m squared 4 straight pi end fraction
increment straight v space equals space fraction numerator 1 over denominator 2 straight m end fraction square root of straight h over straight pi end root

The uncertainty principle in terms of energy and time is given as

increment straight E. increment straight t space greater or equal than space fraction numerator straight h over denominator 4 straight pi end fraction

477 Views

4.

Number of moles of MnO4- required to oxidies one mole of ferrous oxalate completely in acidic medium will be 

  • 0.6 mole

  • 0.4 mole

  • 7.5 mole

  • 7.5 mole


A.

0.6 mole

MnO subscript 4 superscript minus space plus space 5 straight C subscript 2 straight O subscript 4 superscript 2 minus end superscript space plus space 24 space straight H to the power of plus space rightwards arrow space 3 space Mn to the power of 2 plus end exponent space plus space 10 CO subscript 2 space plus 12 space straight H subscript 2 straight O
because space Number space of space moles space of space MnO subscript 4 superscript minus space required space to space space oxidise space 5 space moles space of space straight C subscript 2 straight O subscript 4 superscript 2 minus end superscript space equals 3
therefore space Number space of space moles space of space MnO subscript 4 superscript minus space required space space to space oxidise space 1 space mole space of space straight C subscript 2 straight O subscript 4 superscript 2 minus end superscript space equals space equals 3 over 5 space equals space 0.6 space mol
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5.

The correct order of decreasing second ionisation enthalpy of Ti (22), V (23), Cr(24) and Mn (25) is 

  • Cr > Mn> V > Ti

  • V > Mn > Cr >Ti

  • Mn > Cr> Ti >V

  • Mn > Cr> Ti >V


A.

Cr > Mn> V > Ti

The amount of energy required to remove an electron from unipositive ions is called the second IP which generally increases in a period from left to right.
The second ionisation energies of the first transition series increase almost regularly with an increase in atomic number. However, the value for Cr is sufficiently higher than those of its neighbour ie, (Mn). This is due to the stable configuration of Cr3+ (3d5 exactly half filled.)


[Note: The half-filled and completely filled configuration are more stable.]

917 Views

6.

Equal volumes of three acid solutions of pH 3.4 and 5 are mixed in a vessel. What will be the H+ ion concentration in the mixture?

  • 1.11 x 10-4 M

  • 3.7 x 10-4

  • 3.7 x 10-3 M

  • 3.7 x 10-3 M


B.

3.7 x 10-4

[H]+ in mixture

[H]+ of 1st acid x its volume + [H+]
of IInd acid  x its volume + [H+] of 


equals fraction numerator IIIrd space acid space straight x space its space volume over denominator Total space volume end fraction

straight M space equals fraction numerator straight M subscript 1 straight V subscript 1 space plus straight M subscript 2 straight V subscript 2 space plus space straight M subscript 3 straight V subscript 3 over denominator straight V end fraction
Assume the volume of each solution is 1 L.
[H3O+] in solution of pH = 3 is 10-3M
[H3O+] in solution of pH = 4 is 10-4 M
[H3O+] in solution is pH is 5 is 10-5 M
Total space left square bracket straight H subscript 3 straight O to the power of plus right square bracket space equals space space fraction numerator 10 to the power of negative 3 end exponent space plus 10 to the power of negative 4 end exponent plus 10 to the power of negative 5 end exponent over denominator space 3 end fraction
space equals space 0.00037
equals 3.7 space straight x space 10 to the power of negative 4 end exponent space straight M

2181 Views

7.

For the gas phase, reaction,

PCl5 (g) ⇌ PCl3 (g) Cl2 (g)
Which of the following conditions are correct?

  • Δ H = 0 and ΔS > 0

  • ΔH >0 and ΔS > 0

  • Δ H < 0 and ΔS < 0

  • Δ H < 0 and ΔS < 0


B.

ΔH >0 and ΔS > 0

ΔH = ΔE + ΔnRT


Δn = number of moles of product - number of moles of reactants

ΔG = ΔH - TΔS

For a spontaneous process, ΔG must be negative


PCl5 (g) ⇌ PCl3 (g) Cl2 (g)
 In this  reaction
Δn = 2-1 = 1
Thus, ΔH is positive, ie, >0
If ΔH is positive, then  to maintain the value of ΔG negative, ΔS should be positive , ie, ΔS>0.

1482 Views

8.

Which of the following are not state functions?
I) q + W
II) q
III) W
IV) H-TS

  • (I) and (IV)

  • (II) (III) and (IV)

  • (I), (II) and (III)

  • (I), (II) and (III)


D.

(I), (II) and (III)

A state function is the property of the system whose value depends only on the initial and final state of the system and is independent of the path.

Therefore, 

Internal energy (ΔE) = q +W
It is a state function because it is independent of the path. It is an extensive property.

∴ Gibbs energy (G) = H -TS

It is also a state function because it is independent of the path. It is also extensive property. 
Heat (q) and work (W) are not state functions being path dependent.

639 Views

9.

If the concentration of OH- ions in the reaction Fe(OH)3 (s)  ⇌ Fe3+ (aq) + 3OH-(aq) is decreased by 1/4 times, then equilibrium concentration of Fe3+ will increase by 

  • 8 times

  • 16 times

  • 64 times

  • 64 times


C.

64 times

The concentration of solids taken to be unity.

Fe(OH)3 (s)  ⇌ Fe3+ (aq) + 3OH- (aq)

therefore,

K = [Fe3+][OH-]3

Hence, if OH- ion concentration is decreased by 1/4 times. then equilibrium concentration of Fe3+ will increase by 64 times.

1381 Views

10.

The sequence of ionic mobility in aqueous solution is 

  • K+ > Na+ > Rb+ > Cs+

  • Cs+ > Rb+ > K+ >Na+

  • Rb+ > K+> Cs+ > Na+

  • Rb+ > K+> Cs+ > Na+


B.

Cs+ > Rb+ > K+ >Na+

The smaller the size of ion, the greater the degree of hydration.

Mobility space of space ion space in space aqueous space solution
space space space space proportional to space fraction numerator 1 over denominator size space of space ion space in space aqueous space solution end fraction

Generally in a group size or radii of ions increases, So Li has the smallest size thus bind a maximum number of water molecules with itself and becomes largest in size (in aqueous solution). Hence, the order of ionic radii (size) of alkali metal ions in aqueous solution is 

Li+ > Na+ > K+> Rb+ >Cs+

Thus, the order of mobility 


Li+ > Na+ > K+> Rb+ >Cs+
675 Views