Mr. JT
Solid Water Expansion
A. Purpose:
The purpose of this experiment is to show that when water freezes, the
molecules slow down and pull apart from one another.
"As liquid water cools, the molecules move more slowly and pack closer
together, taking up less space. This decrease in volume results in the water
becoming denser. As a result, cold seawater will sink below warmer seawater.
Fresh water also gets denser as it gets colder, but only down to a temperature
of about 4°C (39°F). Below 4°C, fresh water actually gets less dense as it
cools. Why does this happen? It is because of the hydrogen bonding. In the
liquid phase, water molecules are free to get very close to one another to take
full advantage of the hydrogen bonds. As the water begins to freeze, the
molecules actually move apart from one another in order to fit into the
arrangement they must have in the solid phase. Since the molecules are farther
apart from one another in the solid phase, solid water is less dense than
liquid water." (Wile)
The hydrogen bond is really a special case of dipole forces. A hydrogen bond is
the attractive force between the hydrogen attached to an electronegative atom
of one molecule and an electronegative atom of a different molecule. Usually
the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial
negative charge. The hydrogen then has the partial positive charge.
To recognize the possibility of hydrogen bonding, examine the Lewis
structure of the molecule. The electronegative atom must have one or more
unshared electron pairs as in the case of oxygen and nitrogen, and has a
negative partial charge. The hydrogen, which has a partial positive charge
tries to find another atom of oxygen or nitrogen with excess electrons to share
and is attracted to the partial negative charge. This forms the basis for the
hydrogen bond. (Cluster)
A hydrogen bond in chemistry and biochemistry is a type of intermolecular force
between charges located on different molecules or different parts of one large
molecule. Although stronger than most other intermolecular forces, hydrogen
bonds are much weaker than both the ionic and covalent bond.
As the name implies, one part of the bond involves a hydrogen atom. The
hydrogen must be attached to a strongly electronegative heteroatom, such as
oxygen or nitrogen. This electronegative element has the effect of removing the
electron cloud surrounding the hydrogen nucleus, leaving the atom with a
positive partial charge[?]. Because the hydrogen atom
is small on the molecular scale, this partial charge represents a very strong
charge density. A hydrogen bond involves the positive proton (hydrogen nucleus)
becoming attracted to a lone pair of negatively charged electrons on another
heteroatom, the hydrogen bond acceptor.
Despite the implications of the above description, the hydrogen bond is not a
simple electrostatic attraction. It possesses some degree of directionality,
and can be shown to have some of the characteristics of a covalent. This covalency is stronger the more electronegative the donor
atom is, and hence is seen most strongly in the molecule hydrogen fluoride
(HF).
This experiment hopes to show the difference between water when it is frozen
and when it is in a liquid form
This experiment is of interest because it shows how
the water molecules expand instead of compacting
Hypothesis: If the water molecules
expand when frozen, then the water will be above the mark.
B. Equipment:
1. A tall, clear or translucent plastic drinking cup or a 20-oz. empty water
bottle
2. Water
3. A piece of masking tape
C. Procedures:
1. Fill the cup or bottle ¼ of the way with water.
2. Mark the water level by placing a piece of masking tape on the container so
that the top side of the tape lines up with the level of the water.
3. Place the container in the freezer on a flat surface. If using a bottle, do
not put a lid on top.
4. Allow the container to stay in the freezer overnight.
5. Note the level of the ice as compared to the position of the masking tape.
6. Allow the water to thaw in a sink and clean up.
D. Observations:
1. The 20-oz bottle used was filled ¼ of the way with bottled, purified water.
2. A small amount of water was spilled during the filling process.
3. The water level was marked by placing a piece of masking tape on the
container so that the top side of the tape lined up with the level of the
water. This was easy to accomplish.
4. The container was places in the freezer on a flat surface. The bottled was left unstopped. The freezer had a temperature of 28 degrees
and was on setting Number 3.
5. The container stayed in the freezer overnight, approximately 14
hours.
6. The level of the ice was compared to the position of the masking tape.
7. The ice level was almost two inches above the taped line.
8. The water was thawed in a sink and cleaned up without any further spillage.
E. Conclusions:
The conclusion for this experiment is that the water in liquid form expands
when turning in to a solid this happens when the water molecules get below the
temperature of 39oF at this point the molecules must arrange themselves to go
in to a solid form, since this causes them to maintain a distance between
molecules the solid form of water is less dense also causing it to expand.
A way to improve this experiment would be to use a bottle with a lid so that
the effect of the molecules can be seen in a more drastic manner.
An idea for further research would be to use salt water at different levels of
salinity to show what level of salinity water can freeze at.
F. Bibliography:
Online source:
Domain: http://www.elmhurst.edu
Document:
/~chm/vchembook/161Ahydrogenbond.html (Water Cluster)
Online source:
Domain: http://www.ebroadcast.com.au
Document:
/lookup/encyclopedia/hy/Hydrogen_bond.html
Rosenoff, Steven. Classroom/Internet
Lecture.
Seligson, Sherri.
Exploring Creation With Marine Biology. Apologia Educational Ministries, Inc. 2005.
Wile, Dr. Jay L.
Exploring Creation With Physical Science. Apologia Educational Ministries, Inc. 2000.
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