Water is the most abundant substance and a very vital molecule found in living organisms.

It is colorless,
odorless, and tasteless. It is present as a fluid in all cells. Water acts as a heat-exchange agent and as a carrier
in the bloodstream, distributing oxygen, minerals, vitamins, and hormones. Water possesses unique chemical
properties that suit biological systems. This characteristic is the reason why most biochemical reactions take
place in an aqueous environment. Chemically, water is a polar covalent molecule. A molecule of water has
two hydrogen atoms covalently bonded to a single oxygen atom. The polarity and the hydrogen bonds
between its molecules affect the physical properties of water.

Water is an excellent solvent for polar substances. It can dissolve polar compounds, including ionic ones.
Such molecules are called hydrophilic or water-loving. All the major components in cells such as DNA,
proteins, and carbohydrates dissolve in water. On the other hand, it is immiscible with non-polar substances
like hydrocarbons due to hydrophobic interactions.

The strong hydrogen bonds het ween water molecules result in an unusually high heat capacity, heat of
vaporization, and heat of fusion as compared to other liquids. They lead to high boiling and melting points,
and to a high level of surface tension.

Due to water's relatively high specific heat, the human body can absorb or release considerable amounts of
heat without causing more than 1º of change in body temperature. Water serves as the body's thermal
"insulator" or "cushion," helping it maintain a steady temperature despite major changes in outside
temperature.

Liquid and solid water

Ice, like all solids, has a well-defined structure. A water molecule is surrounded by four other neighboring
molecules, two of which are hydrogen-bonded to the oxygen atom on the central water molecule. Each of
the two hydrogen atoms is similarly bonded to neighboring water molecules. When ice melts to form liquid
water, the uniform three-dimensional tetrahedral organization of the solid breaks down
(http://chemistry.about.com/od/waterchemistry/f/Why-Is-Water-The-Universal-Solvent.htm).

Surface tension

Water, as a liquid, has surface tension properties. Surface tension is directly related to the strength of
intermolecular attraction ainong molecules. Water has a high surface tension because of strong hydrogen
bonding among water molecules. An example illustrating surface tension is a needle floating on the surface of
water.

Water in the human body

About 60% of the adult human body consists of water. It is found within cells of the body (intracellular), and
outside the cells (extracellular). Drinking is one of the human body's main sources of water. Foods like fruits,
vegetables, and meats are considered secondary sources. A considerable amount of water, about 350-400
mL/day, is produced metabolically. This is the product of the oxidation of glucose derived from foods. The
amount of water exchanged within the different parts of the body is quite considerable. The kidneys filter
about 180 L/day, returning most of it into the bloodstream. Lymph flow amounts to 1-2.5 L/day, and the
turnover of fluids in the bowel may reach 8-9 L/day.

Water is important to the human body because it hydrates all the polar molecules and serves as a vehicle in
the transportaion of most organic compounds and nutrients, as well as waste materials. Blood and urine are
examples of aqueous body fluids (http://chemistry.about.com/od/waterchemistry/f/Why-Is-Water-The-
Universal-Solvent.htm).

MATERIALS

Distilled water

KCI

NaCl

Sucrose

Cooking oil

Ethanol

Vinegar

Acetone

Powdered milk

Kerosene

Nine test tubes

Pipette

Wax paper

Paper clip

Dropper

100 mL beaker

Spatula

Vortex (optional)
METHODOLOGY

A. Water Solubility

1. Label the test tubes with the names of the samples (KCl, NaCl, sucrose, cooking oil, vinegar, ethanol, milk,
kerosene).

2. Place 2 mL of distilled water in each of the labeled test tubes.

3. Add 2 mL of liquid reagent or a just about a pinch of solid reagent in each test tube.

4. Shake the test tube well. You can also use a vortex to ensure that the water and the reagent are mixed
properly.

5. Observe the solubility. Record your observations in Table 1.1.

B. Surface Tension

1. Place a drop of water on a piece of wax paper. Observe its shape.

2. Put some water in the beaker. Hold the paper clip below the surface of the water, then release it. Observe
what happens.

3. Remove the paper clip and wipe it dry. This time, place the paper clip carefully on the surface of the water.
Observe what happens.

4. Repeat procedure #3 using acetone. Compare the results.

What causes the water molecules to behave in this manner?

EXPERIMENT 1: Properties of Water

GUIDE QUESTIONS

1. Draw the structures of two water molecules bonded by H-bond.

2. Explain why water forms beads on a waxy surface but spreads out on a clean glass surface.
3. Why does ice float on water? What is the biological importance of ice floating on bodies of water such as
ponds, rivers, and lakes during winter?

4. Why is water called the "universal solvent?"

5. What are hypothermia and hyperthermia? What causes these conditions?

6. Discuss the damaging effects of water's high specific heat.