2.2 The Properties of Water

The Water Molecule The Chemical compound for Water is H 2 O Overall, Water is Neutral, because it has same amount of protons (+) as it does electrons (-). From: 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 a 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 Adhesion Less Dense as a Solid Heat Capacity

Solution and Suspensions Water is usually part of a mixture. There are two types of mixtures: – Solutions – Suspensions

Solutions Ionic compounds disperse as ions in water Ionic compounds disperse as ions in water Evenly distributed Evenly distributed SOLUTE SOLUTE – Substance that is being dissolved SOLVENT SOLVENT – Substance into which the solute dissolves

Solution

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 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