Topic: Properties of LiquidsDo Now:

Properties of Liquids• Definite volume

• Indefinite shape

• Particles close together, but can move little bit – Liquids can flow

• Density liquids much greater than gases – Ex: DH2O(l) is 1250x greater than

DH2O(g) at 25C (room temp)

• Liquids can be compressed but change in volume very slight & requires enormous pressure

• Viscosity

• Surface Tensions – Today we will learn about these physical

properties:

Viscosity

• Viscosity = resistance to flow

• Viscosity depends on: –strength of IMF (force between

molecules)–sizes & shapes of molecules–& temperature

• stronger the IMF, the higher the viscosity–as temperature , viscosity –as temperature , viscosity

Where does the Where does the marble drop marble drop fastest?fastest?

Slowest?Slowest?

water

glycerol

See demo (slide 10 of 13)

•engine oil prevents direct metal to metal contact

•thin film oil on surfaces prevents metal from flaking

•if oil too thick, won’t circulate at low temps

•if oil too thin, will lose film strength at high temps

Surface Tension

• Particles at surface of liquid exist in unbalanced environment– No attraction from above to balance attractions

from below

• Surface seeks smallest possible area

• Net attractive force

pulling down

DEMO

Surface Tension

• Surface Tension = E required to ↑surface area = measure of inward pull

• Strong intermolecular attractions

High surface tension

http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_08.JPG

http://www.esb.utexas.edu/mabrybio211/chapter03/08-Surface-Tension-Water.jpg

Washing with cold water

The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unnecessary.

• Increasing heat lowers temperature

• Compounds that lower surface tension of H2O are called SURFACTATS

• Disrupt hydrogen bonds between H2O molecules

• See video

http://www.weeds.iastate.edu/reference/visuals/additives/img007.gif

Don't touch the tent!

Common tent materials are somewhat rainproof in that the surface tension of water will bridge the pores in the finely woven material. But if you touch the tent material with your finger, you break the surface tension and the rain will drip through.

Soaps and detergents

help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.

Capillary Action

• Water forms concave meniscus in glass tube

• Attractive forces between water and glass is greater than attractive forces between water molecules

• Upward movement of liquid in narrow tube = capillary action

Force(Hg-glass) Force(Hg-Hg)

Force(H2O-glass) Force(H2O- H2O)

CONVEX CONCAVE

meniscus meniscus

Force(Hg-glass