2A.4 Intermolecular forces and anomalous properties of water Quiz: Pearson Edexcel Chemistry, Unit 2

The 20 questions

1. Which intermolecular force is present in all molecules?

   • Permanent dipole-dipole forces, which act only between molecules that have a permanent polarity overall
   • Hydrogen bonds, which form only between molecules that contain H bonded directly to N, O or F atoms
   • London forces, or instantaneous dipole-induced dipole interactions
   • Ionic attractions, which hold oppositely charged ions together in a giant lattice of the solid

2. Which molecules can form hydrogen bonds with each other?

   • NH3, H2O and HF
   • BF3, PCl5 and SF6
   • CH3Cl, CCl4 and CO
   • CH4, H2 and CO2

3. Why does water have a higher boiling temperature than hydrogen sulfide, H2S?

   • Water has a larger molar mass than H2S, so its molecules have more electrons and stronger attractions overall
   • Water forms hydrogen bonds between molecules, which are stronger than the permanent dipole forces in H2S
   • Water molecules are ionic, so they are held together more strongly by electrostatic attraction in the liquid
   • H2S molecules form covalent bonds with each other in the liquid, which are weaker than the attractions between water molecules

4. Why is ice less dense than liquid water?

   • Ice has ionic bonds between its molecules that pack more tightly together than the bonds in liquid water
   • Ice contains more molecules per unit volume than liquid water does, so it is packed more densely overall
   • Hydrogen bonds hold the molecules in an open lattice with more space between them
   • Ice has covalent bonds that are shorter than the bonds in liquid water, so the molecules sit closer together

5. Why do boiling temperatures of alkanes increase with chain length?

   • Longer chains are more polar than shorter chains, so they attract one another more strongly in the liquid
   • Longer chains have more hydrogen bonds between their molecules, which need a large amount of energy to break apart
   • Longer chains contain more ions per molecule, which increases the electrostatic attraction between the molecules
   • Longer chains have more electrons and a larger surface area, so the London forces between molecules are stronger

6. Why does branching in an alkane lower its boiling temperature?

   • Branching reduces the surface contact between molecules, weakening the London forces
   • Branching makes the molecules ionic, so they are held together by strong electrostatic attraction instead of forces
   • Branching adds hydrogen bonds between molecules, which makes the branched alkane harder to boil overall
   • Branching adds more electrons to each molecule, which increases the London forces between the molecules greatly

7. Why are alcohols less volatile than alkanes with a similar number of electrons?

   • Alcohols contain ionic bonds that hold the molecules together, which makes them much harder to vaporise
   • Alcohols have more London forces than alkanes of similar size, because the O-H group adds to the surface area
   • Alkanes form hydrogen bonds with each other, which makes them harder to boil than alcohols of similar size
   • Alcohols form hydrogen bonds between molecules, which need more energy to break

8. Why is the boiling temperature of HF higher than that of HCl?

   • HCl molecules form hydrogen bonds with each other, which is why HCl boils at a higher temperature than HF
   • HF is ionic, so its ions are held together more strongly by electrostatic attraction than the HCl molecules are
   • HF forms hydrogen bonds, whereas HCl has only permanent dipole and London forces
   • HF has more protons than HCl, so its molecules have stronger London forces that need more energy to break

9. Which compound has the highest boiling temperature?

   • Butane
   • Propan-1-ol
   • 2-methylbutane
   • Pentane

10. Which alkane has the lowest boiling temperature: pentane, 2-methylbutane or 2,2-dimethylpropane?

    • 2,2-dimethylpropane
    • 2-methylbutane, a branched alkane with a moderate surface area and London forces of medium strength
    • Pentane, a straight-chain alkane with the largest surface area of the three and the strongest London forces
    • Hexane, a straight-chain alkane with more carbon atoms and therefore the strongest London forces of all

11. Predict whether dimethyl ether, CH3OCH3, can form hydrogen bonds with other dimethyl ether molecules.

    • Yes, through the C-H bonds, which are polar enough to form hydrogen bonds with the oxygen atoms of other molecules
    • No, because it has no hydrogen atoms bonded directly to oxygen
    • Yes, through the lone pairs on carbon, which can accept hydrogen atoms from the neighbouring molecules in the liquid
    • Yes, through the O-H bonds, which are polar enough to form hydrogen bonds with the oxygen atoms of other ether molecules

12. Which molecule can form hydrogen bonds with water?

    • CH3Cl
    • CH4
    • CH3OH
    • CH3CH3

13. Explain why NH3 has a higher boiling temperature than PH3.

    • NH3 is ionic, so its ions attract each other more strongly than the molecules of PH3 attract each other
    • PH3 has hydrogen bonds that are stronger than those in NH3, which is why PH3 has the higher boiling point
    • NH3 has more protons than PH3, so its London forces are stronger and it needs more energy to boil overall
    • NH3 has hydrogen bonds between its molecules, whereas PH3 has only weaker dipole-dipole and London forces

14. Explain why methanol dissolves in water much better than halogenoalkanes do.

    • Water has no intermolecular forces at all, so it dissolves nothing that has any capacity for hydrogen bonding
    • Methanol's O-H group forms hydrogen bonds with water, but halogenoalkanes cannot form hydrogen bonds with water
    • Halogenoalkanes are ionic, so they cannot mix with water, which is a covalent liquid made of separate molecules
    • Methanol has a larger molar mass than halogenoalkanes of similar size, so it dissolves more easily in water

15. Predict the trend in boiling temperatures from HCl to HI and explain it.

    • It decreases from HCl to HI, because the molecules become less polar as the halogen atoms grow larger
    • It increases from HCl to HI, because the larger molecules have more electrons and stronger London forces
    • It stays the same from HCl to HI, because all of the hydrogen halides are covalent molecules of a similar type
    • HCl has the highest boiling temperature of the four, because its bond is the most polar of the hydrogen halides

16. Explain why ethanol has a higher boiling temperature than ethane.

    • Ethanol has more protons than ethane, so its molecules have stronger London forces and need more energy to boil
    • Ethane has a higher molar mass than ethanol, so it has stronger attractions and boils at a higher temperature
    • Ethane forms hydrogen bonds that are stronger than the hydrogen bonds between molecules of ethanol in the liquid
    • Ethanol has hydrogen bonds between molecules, which need more energy to overcome than the London forces in ethane

17. Which factor is most important when predicting whether a liquid has a high boiling temperature?

    • The atomic number of the heaviest element in the molecule only, which sets the boiling temperature directly
    • The strength of the intermolecular forces between its molecules
    • The number of covalent bonds inside each molecule, which determines how strongly the liquid holds together overall
    • The colour of the liquid at room temperature, which correlates with the strength of its intermolecular forces

18. Explain why water is a liquid at room temperature while H2S is a gas.

    • Water's hydrogen bonds raise its boiling temperature far above room temperature, whereas H2S has only weak dipole and London forces
    • Water has more protons than H2S, so its molecules are more massive and therefore stay together as a liquid at room temperature
    • H2S has hydrogen bonds that make it volatile, so it boils at a low temperature and forms a gas at room temperature easily
    • Water is ionic, so its ions are held in a lattice that keeps it liquid at room temperature and resists any boiling process

19. Which molecule has the lowest boiling temperature?

    • Butane, C4H10
    • Ethane, C2H6
    • Propane, C3H8
    • Methane, CH4

20. Which hydrogen halide has the highest boiling temperature?

    • HCl
    • HBr
    • HF
    • HI

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