Name: Concept of Viscosity
Uploaded: 2019-07-19
Duration: 4 min 40 s
Description: This video describes the chemistry behind viscosity and why it is different between various liquids. Let us learn this concept from this informative video.

Question

Write a method for measuring the vapour pressure of the liquid

Accepted Answer

Vapour pressure of the liquid at any temperature is defined as the pressure exerted by the vapour of the liquid when it is in equilibrium with the liquid. Vapour pressure increases with an increase in temperature. Manometric method is used to measure the vapour pressure of a liquid. We can use mercury or n-butyl phthalate as a manometric liquid because both the liquid has a low density and low volatility.

Bulb B is filled with the liquid or solution. The air in the connecting tube is then removed with the help of a vacuum pump. When we close the stopcock, internal pressure is generated, which is caused by vapour evaporating from the liquid or solution i.e., on evaporation, the vapour of the solution or liquid exerts pressure on the mercury column at the left limb thereby the mercury column in the right limb pushes up against the atmospheric pressure. Once the equilibrium is established, then there will be no change in height. From the height difference, we can calculate the vapour pressure. The formula used is,

$P = P_{a} + ∆ h$ , where

$P =$ Vapour pressure of the liquid

$P_{a} =$ Atmospheric pressure

$∆ h =$ The difference in the levels in the two limbs of the manometer.

Write a method for measuring the vapour pressure of the liquid

Important Questions on States of Matter : Liquid State

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