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All questions of Liquid Phase – Intermolecular Forces (GC) for MCAT Exam

Direction (Q. Nos. 13-16) This section contains 4 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONE or  MORE THANT ONE  is correct.
Q.
In which of the following I is more volatile than II?
 
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A,B'. Can you explain this answer?

Hansa Sharma answered

I. Intermolecular H-bonding makes boiling point higher than that of I. Thus, I is more volatile 

II. Ortho nitrophenol is more volatile than para nitrophenol because O-Nitrophenol has intramolecular hydrogen bonding whereas para nitrophenol has inter molecular H bonding and so boils relatively at higher temperature
(c) BP of H2O > > H2S
(d) BP of CH3CH2OH (due to H-bonding) > > CH3— O — CH3 

The H-bond is shortest in 
  • a)
    S— H---S 
  • b)
    N— H ... O 
  • c)
    F— H ... F
  • d)
    F— H ... O
Correct answer is option 'C'. Can you explain this answer?

A hydrogen bond is a weak type of force that forms a special type of dipole-dipole attraction which occurs when a hydrogen atom bonded to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons.
F is the most electronegative atom. Hence hydrogen bond is shortest in F - H ........F.

Out of
Q. unstable compound is/are 
  • a)
    I and II 
  • b)
    Only I 
  • c)
    Only II
  • d)
    Only III
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
I. CCI3CH (OH)2 with two — OH groups on same carbon atom is stable due to intramolecular H-bonding.


Among the following sets, highest boiling points are of the species.
I. HF, HCI, HBr, HI
II. H2O, H2S, H2Se, H2Te
III. NH3,PH3, AsH3,SbH3
  • a)
    HF, H2O, NH3
  • b)
    HCI, H2S, PH3
  • c)
    HBr, H2Te, AsH3
  • d)
    HI, H2S, AsH3
Correct answer is option 'A'. Can you explain this answer?

F, O and N are electronegative elements. Thus, HF molecules are associated by intermolecules H-bonding giving it a liquid state and thus highest boiling point out of HF, HCl.HBr and HI.
Similarly, H2O has highest boiling point, and NH3 has highest boiling point.

Number of water molecules directly attached to one water molecule is
  • a)
    1
  • b)
    2
  • c)
    3
  • d)
    4
Correct answer is option 'D'. Can you explain this answer?

Gaurav Saini answered

One water molecule is directly attached to four water molecules. Thus, coordination number of water is 4.

Consider the following compounds
I. HCI
II. HF
III. CH3COOH
IV. CH4
V. CH3OH
VI. CH3COO-
Q. 
H-bonding is not present in
  • a)
    I, III and IV
  • b)
    I, IV and VI
  • c)
    II, III and V
  • d)
    None
Correct answer is option 'B'. Can you explain this answer?

Explanation:

Compounds:
- I. HCI
- II. HF
- III. CH3COOH
- IV. CH4
- V. CH3OH
- VI. CH3COO-Q

H-bonding:
- Hydrogen bonding occurs when a hydrogen atom is bonded to highly electronegative atoms like fluorine, oxygen, or nitrogen.
- It involves a strong dipole-dipole attraction between a hydrogen atom and a lone pair of electrons on a highly electronegative atom.

Analysis:
- Compound I (HCl) and compound IV (CH4) do not have hydrogen atoms directly bonded to highly electronegative atoms like fluorine, oxygen, or nitrogen, so they do not exhibit hydrogen bonding.
- Compound VI (CH3COO-Q) is a salt and does not have hydrogen atoms available for hydrogen bonding.

Conclusion:
- So, the compounds where hydrogen bonding is not present are I, IV, and VI.
- Therefore, the correct answer is option B (I, IV, and VI).

Which of the following correctly represents H-bonding?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

Nilesh Chawla answered
H-bonding is between polar and electronegative 0, N and F C-atom or H attached to C is not polar. Thus, (a), (c), (d) are incorrect.

Hydrogen bonding plays a central role in the following phenomenon
[JEE Advanced 2014]
  • a)
    ice floats in water
  • b)
    higher Lewis basicity of primary amines than tertiary amines in aqueous solution
  • c)
    formic acid is more acidic than acetic acid
  • d)
    dimerisation of acetic acid (in benzene
Correct answer is option 'A,B,D'. Can you explain this answer?

Rahul Bansal answered
Hydrogen bonding is responsible for the open-cage structure of ice which explains why the density of ice is less than water. 
Primary amines can stabilize themselves by forming hydrogen bonds. Although tertiary amines can also participate in H-bonding the extent is much lesser. 
The + I effect of the CH3  is responsible for the weakening in acidic strength. 
Dimerisation here is indeed because of H-bonding: 

In which of the following boiling point of Column I is not higher than that of Column II?
  • a)
    a
  • b)
    b
  • c)
    c
  • d)
    d
Correct answer is option 'C'. Can you explain this answer?

Bibek Desai answered
(a) Intermolecular H-bonding, boiling point increases with molecular weight for compounds within the same family.
(b) H-bonding is absent is CH3CH2CH3.
(c) Methanol is the larger molecule but H2O has more H-bonding because of two O—H bonds.
Thus, boiling point of H2O(ll) > CH3OH(l).
(d) Molecular weight of butanol is much higher and overcomes attractive forces of butanol.

In the following compounds, select the points of interm olecular H-bonding (linear),
  • a)
    1, 2, 3
  • b)
    1, 3, 4
  • c)
    1,2,4
  • d)
    1,4
Correct answer is option 'D'. Can you explain this answer?

Arindam Unni answered

1. Enoiic H, acidic and polar takes part in H-bonding.
2. 3° alcohol least acidic maximum basic.
3. Carbonyl oxygen is not involved.
4. Acidic and polar H, takes part in H-bonding.

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