PROPERTIES OF MATTER AND THEIR MEASUREMENTS
PROPERTIES OF MATTER AND THEIR MEASUREMENT :-
All substances have unique or characteristic properties.Now,here we are going to study about properties of matter and their measurement . These properties can be classified into two categories - physical properties and chemical properties .
PHYSICAL PROPERTIES OF MATTER :-
"Physical properties are those properties which can be measured or observed without changing the identity or the composition of the substance." Some examples of physical properties are ;- color, odor, melting point, boiling point, density, etc.
CHEMICAL PROPERTIES OF MATTER :-
"Chemical properties, on the other hand, are those properties whose measurement or observation require a chemical change to occur." The examples of chemical properties are ;-
In everyday life, we come across a number of measurements like kilograms (for mass), litres (for volume), meter (for length measurements) etc. In addition to these common measurements we need to measure a number of other quantities as concentration, temperature, pressure, density, amount of electrical charge etc.
"All such quantities which we come across during the Scientific studies are called physical quantities".physical quantity is expressed in two parts, a numerical coefficient and a unit. Either of them is meaningless without the other.
Every measurement gives a numerical result that has three important aspects: (i) Numerical magnitude,(ii) Accuracy and (iii) Indicator of scale ie., unit employed to express. The measurement of physical quantities becomes scientifically more correct and relevant if all the three aspects as given above are reported. Thus,
"A unit may be defined as the standard of reference chosen to measure or express any physical quantity".
INTERNATIONAL SYSTEM OF UNITS (SI)
The International System of Units (in French Le Systeme International d'Unités)abbreviated as SI was established by the 11th General Conference on Weights and Measures (CGPM)
In 1960, the International Committee of Weights and Measures recommended the use of International System of Units, abbreviated as SI Units. SI units are largely a modification of metric system. The seven basic units in SI system are given in below table;-
The definition of all the base units are given in below table;-
Prefixes for Expressing the Decimal Fractions in the SI System
The idea of using prefixes is illustrated by an example below: A hundredth of a metre, corresponding to 10-2, is a centimetre for which the symbol cm is used. Similarly for 103 metre we can use the term kilometre, symbolized as km.
Remember Some Important Facts about S.I. Units
- In chemistry Angstrom, abbreviated as Å is commonly used as a unit of length because it is almost of the size of an atom. However, it does not belong to international system of units. In SI units we are supposed to use nanometers (nm) or picometers (pm).
- By conventions the unit named after the scientist, is written by starting with small letter and not with capital letter. For example, unit for pressure is written as pascal and not as Pascal. Likewise unit of heat or work is written as joule and not as Joule.
- Abbreviations of units do not have a plural ending. For example it is incorrect to write 20 cms. It should be 20 cm.
- Prefixes are used with the basic units e.g., kilometre is equal to 1000 m (meter (m) is the basic unit)
- Till 1964, a litre was defined as a volume of 1 kg of water at 1°C. Accordingly millilitre was a little larger than cubic centimetre. In 1964, a litre was redefined as exactly equal to 1000 cubic centimeter, thus. removing the confusion,
DERIVED UNITS
There are many derived units. These units commonly used SI derived units are given in below table.These derived units are obtained by combination of basic units. For example;- square metre (m²) is the unit for area and the cubic metre (m) is the unit for volume.
MASS AND WEIGHT
Mass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity.
Analytical balance.
The mass of a substance can be determined very accurately in the laboratory by using an analytical balance.
Volume
Volume has the units of length. So in SI system, volume has units of m. But since smaller volume are used in laboratories,e.g.- the units of cm3
Some Common SI Derived Units
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