2.2 The Properties of Water

The Water Molecule The Chemical formula for Water is H 2 O Overall, Water is Neutral, because it has same amount of protons (+) as it does electrons (-). The breakdown: Oxygen has: 8 (+) and 8 (-) 2x Hydrogen has: 2 (+) and 2 (-) Total: 10 (+) 10(-) NEUTRAL!

...HOWEVER, There’s more to H 2 O With 8 protons, water’s Oxygen atom has a stronger pull on the electrons in the molecule than the single protons found in each Hydrogen atom.

THE RESULT: electrons spend more time around the oxygen atom than the 2 hydrogen atoms. Therefore, water has a partial negative charge at one end, and a partial positive charge on the other. Due to this “uneven sharing” of electrons, the water molecule is said to be POLAR. – Water molecules are partially negative by the Oxygen atom. – Water molecules are partially positive by the 2 Hydrogen atoms.

Because of their partial positive and negative charges, polar molecules such as water can attract each other. The attraction between a hydrogen atom with a partial positive charge and another atom with a partial negative charge is known as a Hydrogen Bond.

Because water is a polar molecule, it is able to form multiple hydrogen bonds, which account for these special water properties: Cohesion and Adhesion Less Dense as a Solid High Heat Capacity Water is a Universal Solvent

Cohesion – an attraction between molecules of the same substance. Water on Wax paper

Adhesion – an attraction between molecules of different substances. Water on a Glass surface

Water is less dense as a Solid What does this mean? ICE FLOATS!

Water has a High Heat Capacity Or simply, Water can hold onto lots of Heat Energy This is important for a few reasons Oceans temps stay relatively stable for aquatic life. 2. A Cell’s activity generates lots of heat, heat that is readily absorbed and managed by WATER.

Rarely does Water exist in its pure form It is typically part of a Mixture. There are 2 main types of mixtures: 1. Solutions 2. Suspensions

1.Solutions – type of mixture in which all components are evenly distributed. There are 2 parts to any solution 1. Solvent – substance that does the dissolving. 2. Solute – substance that is dissolved in a solution Water is known as a Universal Solvent

Solutions continued Example – When Table Salt (the solute), is placed in water (the solvent), the water dissolves it. A solute dissolves in the solvent.

2. Suspensions –

Suspensions don’t dissolve but separate Substances that don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended Water keeps the pieces suspended so they don’t settle out.

Acids, Bases, and pH The separation of water molecules into ions causes solutions to be acidic, basic, or neutral. H 2 O  H + and OH - The pH scale measures how acidic or basic a solution is. – pH of 7—Neutral: Equal concentrations of H + and OH - – pH below 7—Acidic: Relatively high concentration of H + – pH above 7—Basic: Relatively high concentration of OH -

Acids, Bases and pH One water molecule in 550 million naturally dissociates into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) Hydrogen Ion Hydroxide Ion Acid Base Acid Base H 2 O  H + + OH -

The pH Scale concentration of H + ions Indicates the concentration of H + ions 0 – 14 Ranges from 0 – 14 7 is neutral pH of 7 is neutral 0 up to 7 is acid pH 0 up to 7 is acid … H + above 7 – 14 is b pH above 7 – 14 is basic… OH - 10X Each pH unit represents a factor of 10X change in concentration pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6 pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6

Acids Strong Acids have a pH of 1-3 Strong Acids have a pH of 1-3 Produce lots of H + ions Produce lots of H + ions

Bases Strong Bases 11 to 14 Strong Bases have a pH of 11 to 14 lots of OH - ions Contain lots of OH - ions and fewer H+ ions

Buffers Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). Produced naturally by the body to maintain homeostasis Produced naturally by the body to maintain homeostasis Weak Acid Weak Base