Properties and Conditions
Matter is described, identified, tested, and evaluated by studying its charactersitics under known conditions. These charactersitics or properties, as they are called, may be divided into many classes. Schemes for such classification, however, may not all be based on the same criteria, and even if they are, differences are bound to arise in definition or interpretation of these criteria. For these reasons, in the following classification there is considerable overlapping so that some properties and some condiitons could, with equal justification, be placed in other classes.
I PHYSICAL PROPERTIES
These can be determined independantly of other substances and without a change in composition, although a structural change may occur. Physical properties may be subdivided as follows:
D. Electrical and Magnetic
II. ATOMIC AND NUCLEAR CONSTANTS AND PROPERTIES
III CHEMICAL PROPERTIES
These determine the ability of a substance to change into one or more other substances. These other substances have diffenr compositions and different properties. Chemical properties are concerned with such questions as:
1. Does the substance
IV PHYSICO-CHEMICAL PROPERTIES
V ORGANLEPTIC PROPERTIES
These have an effect on the human senses, especially taste and smell. These properties are often employed in the examination of food accessories.
A Physical Senses
B Chemical Senses
VI PHYSIOLOGICAL, PHARMACOLOGICAL, AND TOXICOLOGICAL PROPERTIES
VII ADDITIVE PROPERTIES
These are properties which are equal to the sum of the properties of the atoms and the linkages in a molecule. For example: in inorganic chemsitry the properties of a salt are the sum of the properites of the ions. Molar volue is partly an additive property.
VIII COLLIGATIVE PROPERTIES
These are properties of a solution that are dependant upon the number of dissolved particles, whether ions or molecules, and not upon their nature.
IX CONSTITUTIVE PROPERTIES
These are accidental characteristics of a particular specimen only such as length, width, volume, mass, internal energy, and shape. Attributes are sometimes called extensive properties which depend upon the amount of substance involved.
These are qualitites which can be more or less changed at will and which must be stated or understood when the properties of a substance are described, since such properties are dependant upon the conditions.
A. Temperature affects many properties, such as
Some Thermochromic Compounds
B. Pressure affects properties, such as
C. Electric charge on a particle determines its
behaviour in an electric field and in the presence
D. Concentration affects properties, such as
1. Odour. Methyl benzoate is unpleasant in concentrated form but diluted it has the odour of new-mown hay.
2. Toxicity. Fluoride in water in a concentration of 1 ppm gives some protection against dental caries. Higher concentrations give rise to a condition known as mottled enamel. In large doses fluoride is toxic.
3. Rate of reaction.
4. Colligative properties. The freezing point of water containing antifreezes, for example, will depend upon the concentration of the antifreeze.
E. Velocity. According to the theory of relativity the mass of a particle will vary with its velocity.
m = mo / ( 1 - v2/c2 )-2
where m is the mass of the aprticle moving with velocity v with respect to the observer, mo is the mass at rest with respect to the observer and c is the velocity of light. It is readily seen that a particle travelling with the speed of light should have infinite mass.
2. Cleavage of crystals is often a directional property. For example, mica cleaves in thin sheets.
3. Hardness of different
faces of a crystal may be different. For example the octahedral faces
4. The observed colour may
vary depending upon whether observed by reflected or
5. The linear coefficient
of expansion of crystalline substances may not be the same in all
G. Particle size may affect properties
2. Silica gel (large surface area) has a greater adsorptive capacity than silica sand.
3. Platinum black is a better catalyst than bulk platinum.
4. The solubility of fine
precipitates is greater than coarse precipitates. For example