11.3 Properties of Liquids By: Mira Amin, Katie Blackburn, Neil Marfatia

Viscosity Viscosity – the resistance of a liquid to flow –Stronger the intermolecular forces,  greater the viscosity  slower it flows –Common unit = poise (P) = 1 g/cm-s Usually reported in centipoise (cP) =.01 P Depends on attractive forces b/w molecules –Viscosity increases with molecular weight –Viscosity decreases with temperature

Surface Tension Molecules at the surface experience net inward force –Pulls molecules from surface into interior  lowers surface area –Packs molecules closer together Surface Tension – energy required to increase the surface area of a liquid by a unit amount (units: J/m^2) –Stronger the intermolecular forces, higher the surface tension –Water has high surface tension b/c of strong hydrogen bonds

Allows water striders to “walk” on water Coin floats on water A soap bubble balances surface tension forces against internal pneumatic pressure. Dew forming on a leaf

Surface Tension Cohesive forces – intermolecular forces that bind similar molecules to one another –Ex: hydrogen bonding in water Adhesive forces – intermolecular forces that bind a substance to a surface –Ex: formation of a meniscus Capillary action – rise of liquids up very narrow tubes –Helps water and dissolved nutrients travel upward through plants

Capillary Action

Chapter Questions 1) How do viscosity and surface tension of liquids change as intermolecular forces become stronger? –b) as temperature increases? 2) Distinguish between adhesive forces and cohesive forces –b) explain the cause for the U-shaped meniscus formed when water is in a glass tube –c) how is the capacity of paper towels to absorb water related to capillary action?

Chapter Answers Higher viscosity and surface tension –As temp. increases, viscosity and surface tension decrease Cohesive forces bind similar molecules together, while adhesive forces bind a substance to a surface –Meniscus forms b/c adhesive forces b/w H 2 O and glass are greater than cohesive forces b/w H 2 O molecules –Liquid adheres to the paper towel

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