Question

The viscosity of liquid is maximum in:
A.Water
B.Glycol
C.Acetone
D.Ethanol

Answer 1

We can define viscosity as the resistance to flow. For liquids, the larger the intermolecular forces higher the viscosity. The other factors that affect viscosity are temperature and the molecular shape. Higher temperatures correspond to higher average kinetic energies and faster moving molecules.

Complete step by step answer:
We know that intermolecular forces are electrostatic in nature and include van der Waals forces and hydrogen bonds. We know that molecules in liquids are held to other molecules by intermolecular interactions that are weaker than the intramolecular interactions that hold the atoms together within molecules and polyatomic ions. We classify the major types of intermolecular interactions as,
Dipole-dipole interactions
London dispersion forces
Hydrogen bonds
We know viscosity is the resistance of a fluid to flow. The stronger the intermolecular forces between the molecules in a liquid, the more viscous a liquid becomes.
Hydrogen bonding is the strongest intermolecular attraction. So the liquid, with highest intermolecular attraction will have highest viscosity.
Hydrogen bonding can be found in liquids having $- OH$ groups.
In ethanol, there is only one $- OH$ group and it shows the presence of hydrogen bonding.
In glycol, there are two $- OH$ groups and it shows stronger intermolecular bonding than ethanol due to presence of two $- OH$ groups.
Acetone does not show hydrogen bonding. Therefore, option (C) is incorrect.
Water shows the presence of hydrogen bonding.
Among glycol, ethanol and water, the liquid with maximum viscosity is glycol because glycol exhibits stronger hydrogen bonding than ethanol and water due to the presence of two $- OH$ groups.

$\therefore$ Option (B) is correct.

Note:
We have to know that viscosity of the substance decreases with the increasing temperature. At high temperature, the force of attraction between the molecules decreases and due to the high kinetic energy in the molecules the intermolecular forces slips past each other in the layer and these results in decreased viscosity.The shape of the molecule also affects the viscosity, as the molecules with many branched or links will be harder to slide-by one another than small round molecules.
For example,
Carbon tetrachloride has a boiling point of $350\,K$ and propanol has a boiling point of $370\,K$. Carbon tetrachloride has a tetrahedral shape while propanol has a linear carbon chain. Propanol is likely harder to flow because of its shape. The viscosity of propanol is about twice that of carbon tetrachloride.