PHYSICAL PROPERTIES can be determined without changing the chemical composition of the compound. By determining physical properties, chemists are able to classify compounds. Some physical properties include:

1. Color
2. State of matter - is it a solid, liquid or gas?
3. Melting point - the temperature range at which the substance melts, when it changes from a solid state to a liquid state. The melting point of a substance can be measured using several techniques. The most common apparatus used is called a Mel-Temp. You can watch a video demonstrating the determination of melting point using a Mel-Temp on the videos webpage.
4. Boiling point - the temperature at which the substance boils, when it changes from a liquid state to a gaseous state.
5. Solubility - the amount of a compound which can dissolved in a given mass of a solvent such as water. The phrase "like dissolves like" indicates that a knowledge of which solvents are effective in dissolving an unknown compound is helpful in characterizing the unknown compound. Polar solvents dissolve other polar molecular compound and ionic compounds. Nonpolar solvents will dissolve other nonpolar molecular compounds. You can watch a video demonstrating the determination of solubility on the videos webpage.

Terms:

1. When referring to a compound in its solid state, the compound is either soluble or insoluble in a solvent.
2. When referring to a compound in its liquid state, the compound is either miscible or immiscible in a solvent.

soluble

insoluble

miscible

immiscible

6. Density - the volume which is occupied by a specific mass of a material, usually given in units of grams per cubic centimeters or grams per milliliter. The density of a liquid can be determined by weighing a exact volume and calculating density using the equation below.

The volume of a solid can be difficult to measure, so its density is determined using a different method. The volume is found by measuring the volume of a liquid that the solid displaces. In the example below, the volume of the compound is 17.2 mL

Volume of water= 15.0 mL

Volume of water + compound = 32.2 mL

7. Electrical conductivity - the ability of a material to conduct an electric current.

   Solids: Of the solid materials, only metals conduct an electric current.
   
   Pure Liquids:
   

   1. Metals in the molten state conduct an electric current
   2. Molten ionic compounds (salts) conduct an electric current because of ion migration.
   3. Molten or liquid molecular compounds do not conduct an electric current since no ions are present, only molecules.

    

   Water Solutions of Compounds: Compounds that dissolve in water to yield solutions that conduct electricity are called electrolytes. Conductivity in water solution is due to the presence of ions. Materials that dissociate 100% into ions are called strong electrolytes. Those that dissociate into ions to a small extent are called weak electrolytes. Compounds that dissolve in water but do not dissociate into ions and whose solutions do not conduct electricity are called non-electrolytes.