Hydrogen bonding and properties of waterEdexcel International A Level Chemistry: Subtopic test

1. 1
   Water is an unusual substance. Ice floats on the surface of liquid water, whereas the solid form of most substances sinks in its own liquid. Each water molecule in ice is held in position by hydrogen bonds.

   (a)

   How does the density of ice at 273 K compare with the density of liquid water at 273 K?

   [1 mark]

   • AIce is more dense than liquid water
   • BIce and liquid water have the same density
   • CIce is less dense than liquid water
   • DIce is more dense, because its molecules are held in fixed positions

   (b)

   How many hydrogen bonds can each water molecule form with its neighbours in ice?

   [1 mark]

   • AFour
   • BTwo
   • COne
   • DSix

   (c)

   Explain why ice floats on liquid water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The boiling temperatures of the hydrides of the Group 16 elements are: hydrogen sulfide, H₂S, 213 K; hydrogen selenide, H₂Se, 232 K; hydrogen telluride, H₂Te, 271 K; water, H₂O, 373 K.

   (a)

   Which statement best explains the increase in boiling temperature from H₂S to H₂Te?

   [1 mark]

   • AHydrogen bonds between the molecules get stronger
   • BThe covalent bonds in the molecules get stronger
   • CThe electronegativity of the central atom increases
   • DThe number of electrons per molecule increases, so London forces get stronger

   (b)

   If water followed the trend in London forces shown by the other three hydrides, its boiling temperature would be expected to be

   [1 mark]

   • Ahigher than 271 K
   • Blower than 213 K
   • Cbetween 213 K and 232 K
   • Dequal to 373 K

   (c)

   Explain why the actual boiling temperature of water is much higher than the value predicted from the trend in the other hydrides.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Methane, CH₄, and water have similar relative molecular masses (16 and 18). Methane melts at 91 K and boils at 112 K. Water melts at 273 K and boils at 373 K. At 273 K the density of ice is 0.92 g cm⁻³ and the density of liquid water is 1.00 g cm⁻³.

   (a)

   Explain why water has much higher melting and boiling temperatures than methane.

   [3 marks]

   (b)

   A sealed steel bottle is completely filled with 500 g of liquid water at 273 K and placed in a freezer. Calculate the volume of the ice that would form and use your answer to explain why the bottle may crack.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Hydrogen sulfide, H₂S, has 18 electrons per molecule, whereas water has 10. Hydrogen sulfide melts at 188 K and boils at 213 K. Water melts at 273 K and boils at 373 K. Water is also unusual because its solid is less dense than its liquid.

   (a)

   A student says: 'Water has a higher boiling temperature than hydrogen sulfide because the O–H bonds are stronger than the S–H bonds.' Evaluate this statement.

   [6 marks]

   (b)

   Explain why ice is less dense than liquid water, and describe what happens to the hydrogen bonds when ice melts.

   [6 marks]

   Total for question 4: 12 marks

End of questions