February 13, 2019 Wednesday
Bedtime Story
Colloid versus Mixture
Last night we saw that blood is a colloid
and not a suspension from the size of particles contained in it and their
tendency to remain afloat.
But blood can also be considered a mixture,
isn’t it?
Well no, at least not technically by the
chemical definition of mixture.
So how does a colloid differ from a
mixture?
Colloid differs from a mixture in that the
solution of a mixture which consists of a solvent and a solute exists in a
single phase.
On the other hand a colloid exists in two
phases – the dispersed phase of the suspended particles and the continuous
phase of the medium of suspension.
Let me clarify what is meant by the word
“phase”.
While it is true that different phases may
also mean different states of matter that is not the true sense of the meaning
of word “phase” that is being used here.
For instance, a glass vessels holding cold
water containing ice cubes can be said to be containing objects that are in
three or even four phases.
Here the ice cubes would constitute one
phase, water the second phase, the humid air atop the water the third phase and
the glass jar itself the fourth phase.
So this is one way of understanding the
word “phase”.
But in the more fundamental sense a phase
is defined as that region of thermodynamic system wherein all physical
properties of matter such as density, chemical composition and so on are
essentially uniform.
To understand why in a solution there
exists only a single phase unlike in a colloid I have to tell you a little bit
about the process of solvation.
In a solution when the solute dissolves in
a solvent the process is called solvation (the term used more commonly is
dissolving or dissolution).
Solvation of a solute in a solvent involves
interaction between the two at the level of chemical polarity.
Solvation is a very interesting process if
you try to imagine in your mind what I will be writing in the lines below.
In solvation the solvent molecules undergo
reorganization to accommodate molecules of solute through the actions of three
forces namely ionic bonding, hydrogen bonds and van der Waals forces.
I must emphasize here that in nature no
true or pure or clean ionic bonding exists (meaning complete transfer of
electron); all ionic compounds have some degree of covalent bonding or electron
sharing.
The result of such an interaction is the
formation of solvent complexes that comprise of ions of solute surrounded by
concentric shell of solvent.
The single most important property that
determines how well a solvent solvates a particular solute is its polarity.
So what is this polarity?
Stay tuned to the voice of an
average story storytelling chimpanzee or login at http://panarrans.blogspot.com
Good night Mon Ami and my fellow cousin ape.
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Another great educator and a teacher that I am aware of is
Professor Subhashish Chattopadhyay in Bangalore, India.
While I narrate stories, Professor Subhashish an electronic
engineer and a former professor at BARC, does and teaches real mathematics and
physics.
He started the participation of Indian students at the
International Physics Olympiad.
Do visit him here:
All his books can be downloaded for free through this link:
For edutainment and English education of your children, I
recommend this large collection of Halloween Songs for Kids:
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