Solutions

SoluteA solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

Solvent

Salt in salt water Sugar in soda drinksCarbon dioxide in soda drinks

Water in salt water Water in soda

“Like Dissolves Like”

Fats Benzene Steroids Hexane Waxes Toluene

Polar and ionic solutes dissolve best in polar solvents

Nonpolar solutes dissolve best in nonpolar solvents

Inorganic Salts Water Sugars Small alcohols Acetic acid

Solubility Trends The solubility of MOST solids

increases with temperature. The rate at which solids dissolve

increases with increasing surface area of the solid.

The solubility of gases decreases with increases in temperature.

The solubility of gases increases with the pressure above the solution.

Therefore…Solids tend to dissolve best when:

o Heatedo Stirredo Ground into small particles

Gases tend to dissolve best when:o The solution is cold

o Pressure is high

Solubility Chart

Saturation of Solutions A solution that contains the maximum

amount of solute that may be dissolved under existing conditions is saturated.

A solution that contains less solute than a saturated solution under existing conditions is unsaturated.

A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

An electrolyte is: A substance whose aqueous solution conducts an electric current.A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current.

Definition of Electrolytes and Nonelectrolytes

The ammeter measures the flow of electrons (current) through the circuit.

If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the

bulb does not glow, the solution is non-conducting.

Electrolytes vs. Nonelectrolytes

1.Pure water2.Tap water3.Sugar solution4.Sodium chloride solution5.Hydrochloric acid solution6.Lactic acid solution7.Ethyl alcohol solution8.Pure sodium chloride

Try to classify the following substances as electrolytes or

nonelectrolytes…

ELECTROLYTES: NONELECTROLYTES:

Tap water (weak) NaCl solution HCl solution Lactate solution (weak)

Pure water Sugar solution Ethanol solution Pure NaCl

Answers to Electrolytes

Ionic Compounds “Dissociate”

NaCl(s) AgNO3(s) MgCl2(s) Na2SO4(s) AlCl3(s)

Na+(aq) + Cl-(aq)Ag+(aq) + NO3

-

(aq)Mg2+(aq) + 2 Cl-

(aq)2 Na+(aq) + SO42-

(aq)Al3+(aq) + 3 Cl-

(aq)

The reason for this is the polar nature of the water molecule…

Positive ions associate with the negative end of the water dipole (oxygen).Negative ions associate with the positive end of the water dipole (hydrogen).

Ions tend to stay in solution where they canconduct a current rather than re-forming a solid.

Covalent acids form ions in solution, with the help of the water molecules.

For instance, hydrogen chloride molecules,which are polar, give up their hydrogens towater, forming chloride ions (Cl-) and hydronium ions (H3O+).

Some covalent compounds IONIZE in solution

Other examples of strong acids include: Sulfuric acid, H2SO4 Nitric acid, HNO3 Hydriodic acid, HI Perchloric acid, HClO4

Strong acids such as HCl are completely

ionized in solution.

Many of these weaker acids are “organic” acids that contain a “carboxyl” group.

The carboxyl group does not easily give up itshydrogen.

Weak acids such as lactic acid usually ionize less than 5% of the time.

Other organic acids and their sources include:o Citric acid – citrus fruito Malic acid – appleso Butyric acid – rancid buttero Amino acids – proteino Nucleic acids – DNA and RNAo Ascorbic acid – Vitamin C

This is an enormous group of compounds; these are only a few examples.

Because of the carboxyl group, organic acids are sometimes called “carboxylic

acids”.