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 waterA 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
H2O and glass are greater than cohesive forces b/w H2O molecules
– Liquid adheres to the paper towel
Bibliography
• http://www.metacafe.com
• http://www.science.uwaterloo.ca/~cchieh/cact/c123/liquid.html
• http://ga.water.usgs.gov/edu/capillaryaction.htm
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• http://palimpsest.stanford.edu/don/dt/dt3713.html
• http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/CapillaryAction/
CapillaryAction.html
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