How Important Is Water???

Water (H2O) 70% of your body is made of water 2/3 of the molecules in your body are water molecules

I. Structure of Water (H2O) Hydrogen atoms have a “positive” charge and oxygen atoms have a “negative” charge. This makes water a polar molecule.

Polar Molecules –have a positive charge on one end and negative charge on the other. Polar molecules and ionic compounds dissolve best in water because they are attracted to the ends of water molecules with the opposite charge. Water is a polar molecule! Since opposite electrical charges are attracted to each other, water molecules tend to “stick” together.

Ionic compounds - are compounds made up of ions Ionic compounds - are compounds made up of ions. These ions are atoms that have a positive or negative charge. Salt (Na+Cl-) is an ionic compound and dissolves in water because each atom has a charge.

Nonpolar Molecules – do not dissolve well in water because the water molecules are more attracted to each other than the nonpolar molecule; nonpolar molecules do not have an electrical charge; nonpolar substances dissolve in oil

Polar Compounds/Ionic Compounds

II. Universal Solvent Water is capable of dissolving a variety of different substances, which is why it is such a good solvent. Water is called the "universal solvent" because it dissolves more substances than any other liquid. Because these substances can dissolve in water, they can more easily move into and out of cells.

III. Properties of Water 1. high specific heat– water heats slowly and retains heat longer than most substances; this allows the temperature of water to remain relatively constant

Why does water not overheat? Water heats slowly and can absorb a lot of heat with only a small increase in temperature Water can retain heat for longer periods of time so temperatures don’t drop as quickly Why does water not freeze?

 IF water tends to overheat in the body, cells maintain homeostasis by releasing excess heat through water evaporation = sweating.

2. cohesion – means water molecules stick to each other. This attraction between water molecules causes a condition known as surface tension. Surface tension prevents the surface of water from breaking easily

3. adhesion – means water molecules stick to other materials; this process creates what is known as capillary action; it allow water to move up the roots & stems of plants against the pull of gravity

acids – a solution that has an excess of H+ (hydrogen) ions III. Acids and Bases H2O H+ + OH- ( HOH ) hydrogen ion hydroxide ion acids – a solution that has an excess of H+ (hydrogen) ions base – a solution that has an excess of OH- (hydroxide) ions

PH Scale: pH – potential of hydrogen; it measures the hydrogen ion concentration in a liquid

EX: A pH of 4 is how much more /Basic /Basic Each whole number on the pH scale represents a factor of 10. EX: A pH of 4 is how much more acidic than a pH of 6? A pH of 2 is how much more acidic than a pH of 5? 100 1000