Chemistry Water, Acids and Bases

Inorganic Chemistry The study of inorganic compounds  water  acids  bases

Water Chemical formula = H 2 O  Properties Cohesive, form H bonds Adhesive, clings to surfaces Polar

Cohesion and Adhesion among water molecules plays a key role in the transport of water against gravity in plants clinging of one substance to another, contributes too, as water adheres to the wall of the vessels. sequoias wood cut

Surface Tension a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.  Water has a greater surface tension than most other liquids  Water behaves as if covered by an invisible film  Some animals can stand, walk, or run on water without breaking the surface

Polarity of Water The molecule has opposite charges on opposite sides polar molecules form H bonds with other polar molecules

Activity Explain why water sticks to your skin when you take your finger out of the water. Explain why these leaves float instead of submerging. Name the property that makes water molecules attach to each other due to its surface charge.

answers Adhesion & cohesion Surface tension Polarity

Water is the Solvent of Life solution = solvent + solute(s)  ex: cup of coffee hot water (solvent) sugar (solute) coffee grounds (solute) Aqueous solution  The solvent is water ramsey.k12.nj.us

Water Forms Hydrogen Bonds With Ions  The Na+ cations form hydrogen bonds with partial negative oxygen regions of water molecules.  The Cl- anions form hydrogen bonds with the partial positive hydrogen regions of water molecules.  Hydration shell - each dissolved ion is surrounded by a sphere of water molecules

Polar molecules are also soluble in water. Even large molecules, like proteins, can dissolve in water if they have ionic and polar regions.

Hydrophilic  any substance that has an affinity for water Some are water-soluble  water molecules are attracted to molecules with an electrical charge (ionic or polar bonds)  H-bond formation may form

Hydrophobic Substances that have no affinity for water  Non-ionic & non-polar compounds are repelled by water Water-insoluble Hydrophobic molecules are major ingredients of cell membranes Some vegetables and fruits with non-polar pesticides

Mole concept Counting individual or even collections of molecules is not practical Instead, we can use the concept of a mole to convert weight of a substance to the number of molecules in that substance and vice versa

Mole (mol) Is equal in number to the molecular weight of a substance, but up scaled from daltons to grams  Ex. a mole of sucrose (C 12 H 22 O 11 ) C = 12 daltons x 12 H = 1 dalton x 22 O = 16 daltons x 11 Sucrose molecular weight = 342 daltons one mole of sucrose = 342 g

Avogradro’s number The actual number of molecules in a mole x  A mole of sucrose contains x molecules weighs 342g

Molarity the concentration of a material in solution  one molar solution has one mole of a substance dissolved in one liter of solvent, typically water. Example: to make a 1 molar (1 M) solution of sucrose add water to 342 g of sucrose until the total volume is 1 liter and all the sugar is dissolved

2 H 2 O H 3 O+ + OH- by convention: H 2 OH+ + OH- pH of pure water is 7 (10 -7 M) hydronium hydroxide Ionization of Water

pH Scale 0-14  logarithmic scale  pH = - log 10 [H+] acid pH< 7 base pH>7 neutral pH = 7  pure water at RT: pH = -log M = -(-7) = 7

Neutral Solution In a neutral solution [H+] = [OH-] = M, and the pH = 7. Values for pH decline as [H+] increase. While the pH scale is based on [H+], values for [OH-] can be easily calculated from the product relationship [H+] + [OH-] = 14

Acids substances that increase [H+] in solution pH below 7  ex: HClH+ + Cl -  acid precipitation, with pH < 5 acid indigestion use antacids

Bases substances that reduce [H+] in solution pH above 7  NH 3 + H+ NH 4 +  NaOH Na+ + OH- ammoniaammonium ion sodium hydroxidesodium hydroxyde ion ion

Activity Rain has a pH of 5.  Is it an acid, base or neutral?  What is the concentration of H ions?  What is the concentration of OH ions?

answers Rain has a pH of 5.  acid  [H+] = M  [OH-] = M

Buffer prevents sudden pH changes in biological fluids accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted H2CO3 HCO3- + H+ carbonic acid bicarbonate ion hydrogen (donor of H+) (receptor of H+) (ion) The End