Chemistry Podcast

Friday, 4 February 2022

What is Viscosity in Chemistry

What is Viscosity in The Field of Chemistry

What is Viscosity
Do you know! “What is viscosity in chemistry“. To understand about viscosity, we take example of some liquids like Honey and Water. As we know honey is thicker than water. So honey flow with very slow speed on floor than water, as water is very less thick so it flows quickly. 
Hence we can say that liquids with high thickness (like honey) flow slowly and have high viscosity while a liquid with low thickness (like water) flows quickly and have low viscosity.

Example of Viscosity

To understand viscosity very well, just take few examples of viscosity in daily life.
  • Cooking Oil
  • Honey
  • Lubricant
  • Engine Oil
  • Brake Oil
  • Liquid Soap
These highly viscous liquids are some examples of viscosity in science. You known viscosity very well, even before listening this term viscosity in your physics & chemistry class.

Definition of Viscosity

Viscosity can be defined as the fluids resistance to flow.

What is Viscosity

In chemistry, Viscosity of a fluid is the measure of its resistance to gradual deformation by the tensile stress or shear stress. We can also say that viscosity is the internal resistance of the fluid. Fluids which have high viscosity resists to move as its molecular makeup gives this fluid a too much internal friction to motion, while fluids which have low viscosity resists less to move as its molecular makeup gives this fluid a less internal friction to motion.
So, we can say that molecular makeup decides internal friction between them and which ultimately provides viscosity of fluid. Honey has high internal friction than water so honey have high viscosity than water.

What is Meaning of Viscous

To understand viscosity. First, we learn what is the meaning of word “Viscous”. So, viscous is property of material i.e. material having a thick, sticky consistency between solid and liquid and also having a high viscosity. 

Who Poses Viscosity

Along with liquids or fluids, gases also have viscosity but it is very difficult to notice viscosity of gases at ordinary conditions.
We learn this chemistry topic under chemistry terminology category and Physical Chemistry Notes by Chemistry Notes Info in simple way, we can say that, “Viscosity is the resistance of a fluid to change in its shape”,  viscosity is resistance to flow. Fluidity is the reciprocal of viscosity, So now we can say that honey has high viscosity and low fluidity while water has low viscosity and high fluidity.
Viscosity play very important role in determining characteristics of fluids used in lubrication and transportation, spraying, surface coating, injection molding etc.

Formula of Viscosity

Viscosity of any liquid can be calculated with viscosity formula. And viscosity formula is given below to calculate viscosity of any fluid or liquid.
Viscosity = Force×Time ∕Area

Newton’s Viscosity Law

According to the Newton’s viscosity law’, Shear stress between the two adjacent fluid layers is directly proportional to the velocity gradients between these two layers.

Unit of Viscosity

Unit of Viscosity is Newton second per Square meter (Ns/m2)
SI unit of viscosity is Pascal second (Pas)

Relation of viscosity with temperature

Viscosity of the liquids decreases quickly with increase in the temperature, while viscosity of the gases increases with increase in the temperature.
Temperature ->27 °C77 °C
Viscosity of Water0.85×10-3 pascal second0.36×10-3 pascal second
Viscosity of Air1.85×10-5 pascal second2.08×10-5 pascal second

Types of Viscosity

Viscosity is classified in two types. which are as follows-

1. Dynamic Viscosity

Dynamic viscosity is defined as the measure of the ratio of 'shear stress to shear rate' of the fluid.

Formula of Dynamic Viscosity
Dynamic Viscosity - Types of viscosity in science chemistry physics

2. Kinematic Viscosity
Kinematic viscosity is defined as the measure of ratio of 'viscous force to inertial force' on the fluid.

Formula of Kinematic Viscosity

Measurement of viscosity
Viscosity is measured by various types of Rheometers or Viscometers.

1 comment:

Anonymous said...

Very Nice Explanation.

hydrometer (show relative density(specific gravity) on hydrometer graduated scale).
Density of substance = reading at hydrometer x density of water at that temp. of substance

weighing balance
ostwald viscometer
graduated cylinder

Relative density = hydrometer
Specific gravity is the density of a substance divided by the density of water.
Since (at standard temperature and pressure) water has a density of 1 gram/cm3,
and since all of the units cancel, specific gravity is usually very close to the same value as density (but without any units).

Specific gravity = Density of substance/density of water = weight of substance/weight of water

How tightly packed = how much / how big
Density = Mass / Volume

Instruments used to measure viscosity
Capillary Viscometer (The earliest methods for measuring viscosity were based on using capillary tubes and measuring the time it took for a volume of liquid to pass through the length of the tube.- Ostwald or Ubbelohde viscometers)
Zahn Cup (which is a small container with a handle, and a small hole in the bottom. The time it takes to empty the cup through the hole is correlated to viscosity. The Zahn cup is often used in the paint industry.)
Falling Sphere Viscometer (Falling Sphere Viscometer)
Vibrational Viscometer (Vibrational Viscometers measure the damping of an oscillating electromechanical resonator immersed in a fluid. This technique is often used in-process to give continuous readings in a product stream, batch vessel, or in other process applications.)
Rotational Viscometer (The rotational viscometer measures the torque required to turn an object in a fluid as a function of that fluid’s viscosity. This method is frequently used in quality control, and in production laboratories.)

Determination of viscosity of liquid using ostwald viscometer
V1 =((D1T1)/(D2T2))xV2
V1 = Viscosity of unknown liquid (Whoes to be calculated)
D1 = Density of unknown liquid
t1 = Time of flow of unknown liquid
V2 = Viscosity of standard liquid
D2 = Density of standard liquid
t2 = Time of flow of standard liquid

Distilled water
Ostwald viscometer
Electronic balance


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