Q.Alcohols are more soluble in water in comparison of hydrocarbons of comparable molecular weight. Explain.

Showing the 12 most recent of 21 on this concept.

1. CBSE 2026Set ANNUAL1 mark
   Q.Alcohols are more soluble in water than hydrocarbons of comparable molecular masses. Why?

   ›Reveal solutionSolution

   Solubility in water depends on the ability to form hydrogen bonds with water; alcohols have a polar -OH group that hydrogen-bonds with water, whereas hydrocarbons are non-polar and cannot.

   Water is a highly polar, hydrogen-bonding solvent. A solute dissolves well in water when it can interact with water molecules through similarly strong intermolecular forces (like dissolves like).

   • Alcohols contain a polar -OH group. The oxygen's lone pairs and the O-H hydrogen can both participate in hydrogen bonding with surrounding water molecules, allowing alcohol molecules to be effectively surrounded and stabilised by the solvent (solvation). This makes alcohols appreciably soluble in water, especially the shorter-chain ones. …

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2. CBSE 2026Set ANNUAL1 mark
   Q.Write true or false: Intermolecular hydrogen bond is formed between two different molecules of the same or different compounds.

   ›Reveal solutionSolution

   True. Intermolecular hydrogen bonding occurs between two distinct molecules, while intramolecular hydrogen bonding occurs within one molecule.

   A hydrogen bond forms when a hydrogen atom, covalently bonded to a highly electronegative atom (like F, O, or N), is attracted to a lone pair on another electronegative atom. This attraction can occur:

   • Intermolecularly: between the hydrogen of one molecule and the electronegative atom of a DIFFERENT molecule (which can be of the same compound, e.g., water-water hydrogen bonding, or a different compound, e.g., water-ethanol hydrogen bonding). …

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3. CBSE 2025Set ANNUAL1 mark
   Q.Solubility of water in alcohol is due to ______ bond.

   ›Reveal solutionSolution

   Water dissolves in alcohol because both form intermolecular hydrogen bonds through their -OH groups.

   Both water (H-O-H) and alcohols (R-O-H) have a highly polar O-H bond, with oxygen able to act as a hydrogen-bond acceptor and the O-H hydrogen able to act as a hydrogen-bond donor. When water and alcohol are mixed, new O-H...O hydrogen bonds form between the water and alcohol molecules, similar in strength to the hydrogen bonds broken w …

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4. CBSE 2024Set 56/3/11 markMCQ
   Q.For the following question, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The boiling point of ethanol is higher than that of dimethyl ether. Reason (R) : Ethanol molecules are associated through hydrogen bonding whereas in dimethyl ether, it is not possible.

   ›Reveal solutionSolution

   The key idea is that hydrogen bonding between ethanol molecules creates stronger intermolecular forces than the dipole-dipole forces in dimethyl ether, raising ethanol’s boiling point. The Assertion is true, the Reason is true, and the Reason correctly explains the Assertion — so the answer is (A).

   Let’s unpack this step by step.

   1. What the question is really asking

      You have two organic compounds with the same molecular formula, $\ce{C2H6O}$: ethanol ($\ce{CH3CH2OH}$) and dimethyl ether ($\ce{CH3OCH3}$). Despite having identical molar masses, their boiling points differ sharply — ethanol boils at $78.4^\circ \text{C}$, dimethyl ether at $-24.8^\circ \text{C}$. The Assertion states this fact; the Reason claims the cause is hydrogen bonding in ethanol but not in ether. We need to check both statements and their logical link.

   2. Why boiling point depends on intermolecular forces

      Boiling point is the temperature at which the vapour pressure of a liquid equals atmospheric pressure. To boil, molecules must overcome the attractive forces holding them together in the liquid phase. Stronger intermolecular forces → more energy needed → higher boiling point. The three main types (in increasing strength) are: London dispersion forces (present in all molecules), dipole-dipole interactions (in polar molecules), and hydrogen bonding (a special, very strong dipole-dipole interaction involving H bonded to N, O, or F).

   3. Hydrogen bonding in ethanol — the critical difference

      In ethanol, the —OH group has a hydrogen atom covalently bonded to a highly electronegative oxygen. This creates a large partial positive charge on the H and a large partial negative charge on the O. The H of one ethanol molecule is strongly attracted to the O of another, forming a hydrogen bond. These bonds link ethanol molecules into extended networks, so you need a lot of thermal energy to break them apart and vaporise the liquid.

   4. Why dimethyl ether cannot hydrogen-bond

      Dimethyl ether has an oxygen atom, but every hydrogen is bonded to carbon — not to oxygen. The C–H bond is not polar enough to create the strong partial positive charge needed for hydrogen bonding. The only intermolecular forces in dimethyl ether are weaker dipole-dipole interactions (from the C–O–C dipole) and London forces. That’s why it boils at a much lower temperature. …

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5. CBSE 2024Set ANNUAL1 markMCQ
   Q.The reason for high boiling points of alcohols as compared to isomeric ethers is :

   (a) Solubility of alcohols in water

   (b) High reactivity

   (c) Association of molecules due to hydrogen-bonding

   (d) van der Waals forces

   ›Reveal solutionSolution

   Alcohols have much higher boiling points than isomeric ethers because alcohol molecules are held together by intermolecular hydrogen bonding, while ether molecules are not.

   An alcohol (R-OH) has a polar O-H bond, and the hydrogen (attached to the highly electronegative oxygen) can form a hydrogen bond with the lone pair of oxygen on a neighbouring alcohol molecule. This causes alcohol molecules to associate into chains/clusters through extensive intermolecular hydrogen bonding.

   An ether (R-O-R'), though isomeric in molecular formula and having a similar dipole moment, has no O-H bond, so its molecules cannot hydrogen-bond to each other (only weaker dipole-dipole and van der Waals forces act between ether molecules).

   …

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6. CBSE 2024Set ANNUAL1 markMCQ
   Q.Ethanol and dimethyl ether form a pair of functional isomers. The boiling point of ethanol is higher than that of dimethyl ether, due to the presence of –

   (a) H-bonding in dimethyl ether

   (b) H-bonding in ethanol

   (c) $CH_3CH_2$ group of ethanol

   (d) $CH_3$ group of dimethyl ether

   ›Reveal solutionSolution

   Ethanol's -OH group lets it hydrogen-bond with other ethanol molecules; dimethyl ether has no O-H bond and so cannot hydrogen-bond at all.

   Ethanol ($CH_3CH_2OH$) has an $-OH$ group, allowing intermolecular hydrogen bonding between its molecules — a strong dipole-dipole interaction that raises the boiling point significantly. Dimethyl ether ($CH_3-O-CH_3$) has its oxygen bonded to two carbon atoms, with no O–H bond at all, so it cannot hydrogen-bond (option a is therefore wrong — dimethyl ether has no H-bonding). Its inter …

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7. CBSE 2024Set ANNUAL1 markMCQ
   Q.In which of the following is hydrogen bond not formed?

   (a) CH3COOH

   (b) NH3

   (c) C2H5OH

   (d) CH3COCH3

   ›Reveal solutionSolution

   Acetone lacks an O–H/N–H/F–H bond, so it cannot form (self-associating) hydrogen bonds, unlike the other three.

   • CH3COOH (acetic acid): has O–H → forms strong hydrogen bonds (even dimerizes).
   • NH3: has N–H → forms hydrogen bonds.
   • C2H5OH (ethanol): has O–H → forms hydrogen bonds. …

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8. CBSE 2024Set sz1 markMCQ
   Q.Select the correct one: In which of the following compounds does hydrogen bond occur?

   (a) SiH4

   (b) LiH

   (c) HI

   (d) NH3

   ›Reveal solutionSolution

   Hydrogen bonding occurs in NH3 because nitrogen is small and electronegative enough to polarize the N-H bond strongly, unlike Si in SiH4, Li in LiH, or I in HI.

   A hydrogen bond forms when a hydrogen atom, covalently bonded to a small and highly electronegative atom (N, O, or F), is attracted to a lone pair on a similar electronegative atom of a neighbouring molecule.

   Checking each option: SiH4 -- silicon has low electronegativity (comparable to hydrogen), so Si-H bonds are not polar enough. LiH -- this is an ionic hydride (Li+ H-), not a case of hydrogen bonding between molecules. HI -- although iodine is electronegative, it is too large and its electronegativity too low for the H-I bond to support hydrogen bonding (HI is in fact one of the weakest hydrogen halide acids in this regard). NH3 -- nitrogen is small and sufficiently electronegative, so the N-H bond is polar en …

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9. CBSE 2023Set ANNUAL1 markMCQ
   Q.Alcohol boils at higher temperature than the corresponding hydrocarbon due to

   (a) intermolecular hydrogen bond

   (b) intra molecular hydrogen bond

   (c) van der waal's force of attraction

   (d) dipole-dipole interaction

   ›Reveal solutionSolution

   The –OH group lets alcohol molecules hydrogen-bond to one another, an attraction hydrocarbons of similar mass simply cannot form.

   Alcohol molecules associate with each other through intermolecular hydrogen bonding, since the O–H bond is highly polar (O is electronegative) and each molecule has both an H-bond donor (O–H) and acceptor (lone pairs on O). Considerable extra thermal energy is required to break these hydrogen bonds before the molecules can escape into the vapour ph …

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10. CBSE 2022Set ANNUAL1 markMCQ
    Q.Alcohol are soluble in water because -

    (a) they have higher molecular weight than water.

    (b) they form Hydrogen Bond with water.

    (c) they displace water.

    (d) None of these.

    ›Reveal solutionSolution

    Alcohols dissolve in water because their -OH group can hydrogen-bond with water molecules.

    An alcohol molecule, R-OH, carries a polar -OH group in which the O-H bond is highly polarised. This -OH group can form hydrogen bonds with the -OH of water molecules (both as a hydrogen-bond donor and acceptor), just as water molecules hydrogen-bond with each other. This intermolecular hydrogen bonding lets the alcohol molecules mix intimately with water, so lower alcohols (methanol, ethanol, propanol) are miscible with water in all proportions. As the hydrocarbon (R) part of the alcohol becomes larger, the non-polar part dominates, hydrogen bonding contribution becomes relatively less significant, and solubility in w …

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11. CBSE 2022Set TERM21 mark
    Q.Solubility of alcohols in water is due to their ability to form ................. bonds with water molecules.

    ›Reveal solutionSolution

    Alcohols dissolve in water because the -OH group forms hydrogen bonds with water molecules.

    The -OH group of an alcohol is polar: the oxygen carries a partial negative charge and the H a partial positive charge. Water molecules are similarly polar. When an alcohol is mixed with water, the O-H of the alcohol can hydrogen-bond with the O of water (and vice versa), pulling alcohol molecules into solution.

    …

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12. CBSE 2022Set ANNUAL1 mark
    Q.Why is $H_2O$ a liquid and $H_2S$ a gas?

    ›Reveal solutionSolution

    Oxygen's small size and high electronegativity allow water molecules to hydrogen-bond strongly with each other, raising its boiling point well above room temperature; sulfur's much lower electronegativity and larger size mean H₂S cannot hydrogen-bond significantly, so only weak van der Waals forces hold its molecules together, keeping it a gas at room temperature.

    The role of hydrogen bonding

    A hydrogen bond forms when a hydrogen atom bonded to a highly electronegative, small atom ($F$, $O$, $N$) is attracted to a lone pair on a similarly electronegative atom in a neighbouring molecule. Its strength depends strongly on the electronegativity and size of that atom.

    Comparing O and S

    • Oxygen: electronegativity $\approx 3.44$ (Pauling scale), small atomic radius. The $O-H$ bond in water is highly polar, and oxygen's small size lets neighbouring molecules approach closely enough for a strong hydrogen bond. Each water molecule can form up to 4 hydrogen bonds (2 as donor via its 2 H atoms, 2 as acceptor via its 2 lone pairs), building an extensive 3D hydrogen-bonded network that requires substantial thermal energy to break — giving water its unusually high boiling point ($100^\circ C$) for such a small molecule. …

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