Although steel is denser than water, a steel needle or paper clip placed carefully lengthwise on the surface of still water can be made to float. Explain at a molecular level how this is possible.
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Chemistry 2e · 10.2 Properties of Liquids
Properties of Liquids: practice problems
4 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.
Exercises 25
You may have heard someone use the figure of speech “slower than molasses in winter” to describe a process that occurs slowly. Explain why this is an apt idiom, using concepts of molecular size and shape, molecular interactions, and the effect of changing temperature.
Exercises 27
The surface tension and viscosity of water at several different temperatures are given in this table.
Water Surface Tension (mN/m) Viscosity (mPa s) 0 °C 75.6 1.79 20 °C 72.8 1.00 60 °C 66.2 0.47 100 °C 58.9 0.28 (a) As temperature increases, what happens to the surface tension of water? Explain why this occurs, in terms of molecular interactions and the effect of changing temperature.
(b) As temperature increases, what happens to the viscosity of water? Explain why this occurs, in terms of molecular interactions and the effect of changing temperature.
Exercises 29
Water rises in a glass capillary tube to a height of 17 cm. What is the diameter of the capillary tube?
Key terms · 5
- adhesive force
- force of attraction between molecules of different chemical identities
- capillary action
- flow of liquid within a porous material due to the attraction of the liquid molecules to the surface of the material and to other liquid molecules
- cohesive force
- force of attraction between identical molecules
- surface tension
- energy required to increase the area, or length, of a liquid surface by a given amount
- viscosity
- measure of a liquid’s resistance to flow
Learn 10.2 on the whiteboard
The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.