2. Jens
Martensson
Freezing point, temperature at which a liquid
becomes a solid. For a given substance, the
freezing point of its liquid is the same as the
melting point of its solid form, and depends on
such factors as the purity of the substance and the
surrounding pressure.
The freezing point of water at a pressure of one
atmosphere is 0°C (32°F); that of liquid nitrogen is
-209.89°C (-345.8°F).
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What is freezing
point ?
3. Jens
Martensson
Example …
Snow form a tiny ice crystals in
• Clouds stick together to become
snow flakes. If enough crystals stick
together ,they will become heavy
enough to fall to the ground.
• SNOW is formed when temperatures are
low and there is moisture in the
atmosphere in the form of tiny ice
crystals.
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Martensson
The researchers propose that, since the organisms cannot reproduce below this
temperature, -20 °C Scientists placed single-celled organisms in a watery medium, and
lowered the temperature. As the temperature fell, the medium started to turn into ice
and as the ice crystals grew, the water inside the organisms seeped out to form more
ice. This left the cells first dehydrated, and then vitrified. Once a cell has vitrified,
scientists no longer consider it living as it cannot reproduce, but cells can be brought
back to life when temperatures rise again. This verification phase is similar to the state
plant seeds enter when they dry out. is the lowest temperature limit f‘.The interesting
thing about vitrification is that in general a cell will survive, where it wouldn't survive
freezing, if you freeze internally you die. But if you can do a controlled vitrification you
can survive,' says Professor Andrew Clarke of NERC's British Antarctic Survey , lead
author of the study. 'Once a cell is vitrified it can continue to survive right down to
incredibly low temperatures. It just can't do much until it warms up.'or life on Earth.
More complex organisms are able to survive at lower temperatures because they are
able to control the medium the cells sit in to some extent.
Freezing temperature in living
organisms …
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Martensson
• 'Bacteria, unicellular algae and unicellular fungi – of which there are a huge amount
in the free-living because they don't rely on other organisms ,' Clarke explains.
• 'Everything else, like trees and animals and insects, has the ability to control the fluid
that surrounds their internal cells. In our case it's blood and lymph. In a complicated
organism the cells sit in an environment that the organism can control. Free-living
organisms don't have this; if ice forms in the environment they are subject to all the
stresses that implies.'
Control of freezing temperature in
other organisms…
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Martensson
• Lowering the freezing point of water is easy. All you have to do is add salt, sugar or
any other solute. Going in the opposite direction and raising the freezing
temperature of water is not nearly as easy. In fact, some scientists doubt that it even
be done. However, even though it may be true that you can‘t raise the freezing point
by adding a solute, researchers have discovered other ways to the freezing point of
super cooled water. These methods work only with pure water.
• how to raise the freezing point of liquid?:
• Start With Super cooled Water and Add Alchol: The process by which water
freezes is complicated by the fact that water is a polar molecule, which means that,
even though its net charge is zero, it has a positive and negative end, like a magnet.
Water molecules bind electrically to each other and to impurities in the water by
forming hydrogen bonds, and they coalesce into ice more easily if the water contains
impurities. If you can find a way to suspend a droplet of pure water in the air without
having it touch anything, it could remain in the liquid state at temperatures well
below 0 degrees Celsius (32 degrees Fahrenheit). Such super cooled water can stay
in the liquid state until the temperature falls to -40 C (-40 F).
How to raise freezing point of
water...
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Martensson
• Adding alcohol to the water, however, changes its behavior. When cooled, alcohol
forms ice-like hexagons, and the water droplets coalesce around these instead of
floating freely around each other. The hexagonal structures provide the same type of
stability as solid impurities. By adding alcohol, scientists have found they can raise
the freezing point of pure water to 0 C.
• Lowering the freezing point ;
• The solute you add, but you can't lower the freezing point indefinitely. In fact, the
zero he amount you can lower the freezing point of water depends on the
concentration of point of the Fahrenheit scale (-17.8 C) is defined as the freezing
temperature of a saturated solution of salt water. No more salt will dissolve in a
saturated solution, so 0F is the lowest temperature to which you can lower the
melting point of water with salt. However, it is possible to supercool water to get it
to remain in the liquid state at even lower temperatures. University of Utah
researchers have determined the temperature at which water absolutely has to
freeze to be -48 C (-55 F).
Raise freezing point by alcohol…
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Martensson
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Freezing point as an experiment…
• Perform rapid and inexpensive
measurements.
• Simple and reliable performance industry
preffered freezing point method.
• Eco friendly ,non toxic,non corrosive and
safer to handle and store.
• Foods can be frozen in less time then they
can be dried or canned .
• The most wiedly referenced and practiced
technique for osmolality testing- freezing
point Osmometers have been commercially
available for over 50 years.
• Best menthod to maintain color, texture
,flavor and nutritive value .
Disadvantages
It needs samples of low visscocity.
• May not be suitable for molality
colloidal solutons.
• Storage space limited bY capacity of
freezer.
• Texture of some foods is undesireable
to achieve BECAUSE OF FREEZING
POINT.
• Small fluctuations in storage
temperature can result in thawing into
large lumps .
. Hazardeous conditions of extremely low
temperatures.
Advantages
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Martensson
• FOR EXAMPLE ;
• Find the freezing point when 100g OF MgCL2 are dissolved in 100.0g of H2O.
• Tf =iKfm
• 100g MgCl2 (mol /95.21)
=1.05 moles
Finding molality ;
Moles of solute(mol) / mass of solvent (kg)
100g of H2O (Kg/1000g)
= .100kg
Determining freezing point of solution…
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