Water Activity in Food
Preservation
-solutions
-ions
-properties of water
Salts are IONIC COMPOUNDS
-Ions form between metals and nonmetals.
-All atoms will react until the atoms have 8 electrons in their valence
(outer) shells.
-Watch the animation of sodium reacting with chlorine to form table
salt, sodium chloride (NaCl):
http://www.visionlearning.com/library/module_viewer.php?mid=55
-Other examples of ionic bonding:
http://www.teachmetuition.co.uk/Chemistry/Chemicalstructureandbonding/ionic_bonding.
htm
Properties of Water
http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbonds.html
Water molecule
Water as a Solvent
http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html
Dissolving animation
Water Activity (Aw) and Free Water in
Food Preservation
http://physioweb.med.uvm.edu/bodyfluids/osmosis.htm
Water activity osmosis (follow links to sample problems)
http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf
Salt and free water
REVIEW QUESTIONS
•
What holds ionic compounds together (example: salts?)
•
Water is a molecule with polar covalent bonds. What does polar
mean?
•
Why is water such a good solvent for salts?
•
What does Aw stand for?
•
How can the water activity be decreased?
•
Water moves or diffuses from an area of high water activity to an area
of low water activity.
-At the beginning of the meat experiment, where was
the water activity the highest: inside of the meat or
outside in the bag?
-Would water move from inside meat to outside bag, or
from bag into meat? WHY?????