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Module 9 : Experiments in Chemistry

Lecture 39 : Properties and Equilibria: Viscosity and Partition Coefficient

39.1	Introduction
	Viscosity, one of the transport properties, arises because of intermolecular attractive and relatively long-range forces. Viscosity coefficient (), a specific constant characteristic of a liquid could be expressed by the following equation of Poiseuille.
		(39.1)
	where V is the volume of liquid delivered in time t, through a capillary of radius r and length L, with a hydrostatic pressure P. In an apparatus designed so that equal volumes of liquids can flow through the same capillary of length L and radius r, may be written as
		(39.2)
	If g remains constant in any given location and h, the height through which the liquid falls is kept constant, above equation becomes,
		(39.3)
	where k is the dimensional constant of the apparatus.
	If two liquids are compared using the same apparatus, it follows that
		(39.4)
	If , the coefficient of viscosity of one of the substances, is known from a previous measurement, then , the viscosity of the other liquid, can be calculated from the measured quantities, d₁, d₂ , t₁ and t₂.