Intermolecular ForcesEdexcel International A Level Chemistry: Topic test

1. 1
   A student studies four compounds: methylamine, CH₃NH₂, methoxymethane, CH₃OCH₃, fluoromethane, CH₃F, and ethane, CH₃CH₃.

   (a)

   Between which of these liquids do hydrogen bonds form between the molecules of the same compound?

   [1 mark]

   • Amethoxymethane
   • Bmethylamine
   • Cfluoromethane
   • Dethane

   (b)

   Which statement about London forces is correct?

   [1 mark]

   • AThey exist only between polar molecules
   • BThey arise from permanent dipoles in molecules
   • CThey are always stronger than hydrogen bonds
   • DThey arise because an instantaneous dipole in one molecule induces a dipole in a neighbouring molecule

   (c)

   Explain how a hydrogen bond forms between two molecules of methylamine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Propan-1-ol, propan-2-ol and methoxyethane, CH₃OCH₂CH₃, are isomers with the molecular formula C₃H₈O. Their boiling temperatures are: propan-1-ol 370 K; propan-2-ol 356 K; methoxyethane 280 K.

   (a)

   Which statement explains why propan-1-ol has a higher boiling temperature than methoxyethane?

   [1 mark]

   • APropan-1-ol molecules form hydrogen bonds with each other, but methoxyethane molecules cannot
   • BPropan-1-ol molecules have more electrons, so the London forces are stronger
   • CThe covalent bonds in propan-1-ol are stronger and must be broken on boiling
   • DMethoxyethane molecules have no permanent dipole

   (b)

   Which statement best explains why propan-2-ol boils at a lower temperature than propan-1-ol?

   [1 mark]

   • APropan-2-ol molecules cannot form hydrogen bonds
   • BPropan-2-ol molecules have fewer electrons
   • CPropan-2-ol molecules are more compact, so there is less surface contact and weaker London forces
   • DThe O–H bond in propan-2-ol is non-polar

   (c)

   Butan-1-ol boils at 391 K. Explain why this is higher than the boiling temperature of propan-1-ol.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Glucose, C₆H₁₂O₆, is a white solid that dissolves readily in water but is almost insoluble in hexane. Cooking oil consists of non-polar molecules that mix with hexane but not with water.

   (a)

   Explain why glucose dissolves readily in water.

   [3 marks]

   (b)

   Explain why cooking oil dissolves in hexane but not in water.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Ethane-1,2-diol, HOCH₂CH₂OH (34 electrons per molecule), is used as antifreeze. It boils at 470 K and mixes completely with water. Butane, C₄H₁₀ (34 electrons per molecule), boils at 273 K, and ethanol, C₂H₅OH (26 electrons per molecule), boils at 351 K.

   (a)

   Explain why ethane-1,2-diol has a much higher boiling temperature than butane.

   [6 marks]

   (b)

   Explain why ethane-1,2-diol mixes completely with water, and why it boils at a higher temperature than ethanol.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   The boiling temperatures of the Group 14 hydrides are: methane, CH₄, 112 K; silane, SiH₄, 161 K; germane, GeH₄, 185 K; stannane, SnH₄, 221 K. All four are non-polar, tetrahedral molecules.

   (a)

   Which statement explains the increase in boiling temperature from methane to stannane?

   [1 mark]

   • AHydrogen bonding becomes stronger down the group
   • BThe covalent bonds in the molecules become stronger down the group
   • CThe number of electrons increases, so the London forces become stronger
   • DThe permanent dipoles become larger down the group

   (b)

   Which substance has only London forces between its molecules?

   [1 mark]

   • Abromine, Br₂
   • Bhydrogen fluoride, HF
   • Cammonia, NH₃
   • Dchloromethane, CH₃Cl

   (c)

   Explain why the covalent bonds in silane are not broken when silane boils.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Propanone, CH₃COCH₃ (32 electrons per molecule), is a polar liquid used in nail-varnish remover. It mixes completely with water and boils at 329 K. Butane, C₄H₁₀ (34 electrons per molecule), is non-polar and boils at 273 K.

   (a)

   Which statement explains why propanone mixes completely with water?

   [1 mark]

   • APropanone molecules contain O–H groups that form hydrogen bonds with water
   • BPropanone and water both have only London forces between their molecules
   • CPropanone molecules form hydrogen bonds with one another and so with water
   • DA hydrogen atom of a water molecule forms a hydrogen bond with a lone pair on the oxygen atom of propanone

   (b)

   Why can propanone molecules not form hydrogen bonds with each other?

   [1 mark]

   • AThe oxygen atom has no lone pairs
   • BThey have no hydrogen atom bonded directly to oxygen, nitrogen or fluorine
   • CThe C=O bond is non-polar
   • DThe molecules are too large

   (c)

   Explain why propanone has a higher boiling temperature than butane, even though butane has more electrons.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A sealed bottle contains 500 g of water at 0 °C, with a density of 1.00 g cm⁻³. The water freezes to ice with a density of 0.920 g cm⁻³.

   (a)

   Calculate the volume of the ice and the percentage increase in volume on freezing.

   [3 marks]

   (b)

   Explain, in terms of hydrogen bonding, why ice is less dense than liquid water.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Four compounds, each with 26 electrons per molecule, have these boiling temperatures: propane, C₃H₈, 231 K; chloromethane, CH₃Cl, 249 K; ethylamine, C₂H₅NH₂, 290 K; ethanol, C₂H₅OH, 351 K.

   (a)

   Explain the order of the boiling temperatures of these four compounds.

   [6 marks]

   (b)

   Predict and explain the solubility in water of ethanol, chloromethane and propane, and name a suitable solvent for propane.

   [6 marks]

   Total for question 8: 12 marks

End of questions