Study Set Content:
The pressure of the saturated vapor above the liquid is then known as the
equilibrium vapor pressure
The presence of a gas such as air above the liquid would decrease the rate of evaporation,
, but it would not affect the equilibrium pressure of the vapor.
– used for precise determination of vapor pressure
. Isopiestic method
measure change in potential as a solution as a solution of known vapor pressure and an unknown evaporate in a chamber maintained at constant humidity.
Thermoelectric method
Methods of Determining Vapor Pressure
1. Manometer
2. Isopiestic method
3. Thermoelectric method
The attractive force exerted upon the surface molecules of a liquid by the molecules beneath that tends to draw the surface molecules into the bulk of the liquid and makes the liquid assume the shape having the least surface area.
Surface Tension
Surface tension of a liquid is considered
d two dimensional
Therefore, the dimensions of surface tension are force per unit length: generally, the units used are
dynes.cm⁻ ¹
Generally, the surface tension of liquids decreases with an
increase in temperature
Measurement of surface tension:
: Capillary Method
Reciprocal of fluidity
Viscosity
Force of friction that tends to retard movement in a fluid body
. Viscosity
Resistance of a liquid to flow
Viscosity
– measurement of the fluid’s internal resistancetoflow(expressed as poise or Pa.s)
Absolute/Dynamic Viscosity
viscosity in relation to a standard
Relative viscosity
– absolute viscosity/dynamic viscosity divided by the density of the liquid at a specific temperature. (Stokes or Centistokes
. Kinematic Viscosity
Types of Viscosity
1. Absolute/Dynamic Viscosity
2. Relative viscosity
3. Kinematic Viscosity
– the viscosity of a Newtonian liquid can be determined by measuring the time required for the liquid to pass between two marks as it flows by gravity through a vertical tube (Ostwald Viscosimeter)
Capillary Viscometer
η1d2t2 = η2d1t1
Capillary Viscomete
– the sample is sheared in the space between the outer wall of a bob and the inner wall of a cup into which the bob fits
Cup and Bob Viscometer
