Chemistry

Water, Acids and Bases

Inorganic Chemistry

The study of inorganic compounds water acids bases

Water

Chemical formula = H2O 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 surroundedby 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 (C12H22O11)

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 6.023 x 1023

A mole of sucrose contains 6.023 x 1023 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 H2O H3O+ + OH-

by convention: H2O H+ + OH- pH of pure water is 7 (10-7 M)

+

+-

hydronium hydroxide

Ionization of Water

pH

Scale 0-14 logarithmic scale

pH = - log10 [H+] acid pH< 7 base pH>7 neutral pH = 7

pure water at RT: pH = -log 10-7M

= -(-7) = 7

Neutral Solution

In a neutral solution [H+] = [OH-] = 10-7 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: HCl H+ + Cl - acid precipitation, with pH < 5

acid indigestion use antacids

Bases

substances that reduce [H+] in solution

pH above 7 NH3 + H+ NH4 +

NaOH Na+ + OH-

ammonia ammonium ion

sodium hydroxide sodium 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+] = 10-5 M [OH-] = 10-9 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