# MEASUREMENT OF PHYSICAL QUANTITIES IN CHEMISTRY

One of the
important part of the scientific work is measuring of physical quantities such
as mass, volume, length, energy, temperature, etc. It is interesting to note
that all

these quantities can be expressed in terms of a few basic units. For
example, in everyday life, we come across a number of measurements like
kilograms (for mass), litres (for volume), metres (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”.

A physical
quantity thus refers to the result of measurement operation.

It involves the
comparison of the quantity to be measured with some fixed standard.

For example, if we are interested in Seal
knowing the length of a pencil, the operations would be:

(i) to lay the
pencil parallel to centimeter scale and

(ii) to count
the number of markings on the scale.

Suppose the
number of markings is 9.5. This implies that the piece of paper is 9.5 times
longer than one unit of measurement. It makes no sense to say that length of
paper is 9.5. However, if we attach centimetre, a unit of length, to the numerical
figure, i.e., 9.5 cm, it will become more appropriate. Thus, a measured
physical quantity is expressed in two parts, a numerical coefficient and a
unit.

Either of them is meaningless without the other.

In the
measurement of the length of the pencil, 9.5 is a numerical figure whereas
centimeter is a unit.

The study of
experimental science thus depends upon the quantitative measurement of
properties. Every measurement gives a numerical result that has three important
aspects:

(i) Numerical
magnitude,

(ii) Accuracy
or precision with which the number is expressed and

(iii)
Indicator of scale i.e., 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”.

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