Topic: Properties of Liquids Do 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: D H2O(l) is 1250x greater than D H2O(g) at 25  C (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 marble drop 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

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 H 2 O are called SURFACTATS Disrupt hydrogen bonds between H 2 O molecules See videovideo

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(H 2 O-glass)  Force(H 2 O- H 2 O) CONVEX CONCAVE meniscus meniscus Force(Hg- glass