1.3 Properties of Matter and their Measurement

Every substance has unique or characteristic properties. These properties can be classified into two categories: physical properties and chemical properties, like composition, combustibility, ractivity with acids and bases, etc.

Physical Properties

Physical properties are those which can be measured or observed without changing the identity or composition of the substance such as colour, odour, melting point, boiling point, density, etc.

Chemical Properties

Chemical properties are those which require a chemical change for their measurement like composition, combustibility, ractivity with acids and bases, etc. Measurement of physical properties does not require the occurrence of a chemical change. Examples of chemical properties are characteristic reactions of different substances; these include acidity or basicity, combustibility, etc.

Measurement of physical properties

Many properties of matter are quantitative in nature which can be measured under the following system of units. A common standard system was established in 1960 and is known as the International System of Units (SI). 

The International System of Units (SI)

The SI system has seven base units and they are listed in Table 1.1. These units pertain to the seven fundamental scientific quantities. The other physical quantities, such as speed, volume, density, etc., can be derived from these quantities. These prefixes are listed in Table 1.3.
Let us now quickly go through some of the quantities that you will be often using in this book.

The definitions of the SI base units are given in Table 1.2. The SI system allows the use of prefixes to indicate the multiples or submultiples of a unit.

These prefixes are listed in Table 1.3. Let us now quickly go through some of the quantities which you will be often using in this book.

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. The mass of a substance can be determined accurately in the laboratory by using an analytical balance. The SI unit of mass is kilogram. However, its fraction named as gram \((1 \mathrm{~kg}=1000 \mathrm{~g})\), is used in laboratories due to the smaller amounts of chemicals used in chemical reactions.

Volume

Volume is the amont of space occupied by a substance. It has the units of (length) \({ }^{3}\). So in SI system, volume has units of \(\mathrm{m}^{3}\). But again, in chemistry laboratories, smaller volumes are used. Hence, volume is often denoted in \(\mathrm{cm}^{3}\) or \(\mathrm{dm}^{3}\) units.

A common unit, litre \((\mathrm{L})\) which is not an SI unit, is used for the measurement of volume of liquids.
\(1 \mathrm{~L}=1000 \mathrm{~mL}, 1000 \mathrm{~cm}^{3}=1 \mathrm{dm}^{3}\)

In the laboratory, the volume of liquids or solutions can be measured by graduated cylinder, burette, pipette, etc. A volumetric flask is used to prepare a known volume of a solution. These measuring devices are shown in Fig. 1.6 below.

Density

The two properties – mass and volume discussed above are related as follows:
Density \(=\frac{\text { Mass }}{\text { Volume }}\)
Density of a substance is its amount of mass per unit volume. So, SI units of density can be obtained as follows:
\(
\begin{aligned}
\text { SI unit of density } &=\frac{\text { SI unit of mass }}{\text { SI unit of volume }} \\
&=\frac{\mathrm{kg}}{\mathrm{m}^{3}} \text { or } \mathrm{kg} \mathrm{m}^{-3}
\end{aligned}
\)
This unit is quite large and a chemist often expresses density in \(\mathrm{g} \mathrm{cm}^{-3}\), where mass is expressed in grams and volume is expressed in \(\mathrm{cm}^{3}\). Density of a substance tells us about how closely its particles are packed. If density is more, it means particles are more closely packed.

Temperature

There are three common scales to measure temperature – \({ }^{\circ} \mathrm{C}\) (degree celsius), \({ }^{\circ} \mathrm{F}\) (degree fahrenheit) and \(K\) (kelvin). Here, \(K\) is the SI unit. The thermometers based on these scales are shown in Fig. 1.7. Generally, the thermometer with celsius scale are calibrated from \(0^{\circ}\) to \(100^{\circ}\), where these two temperatures are the freezing point and the boiling point of water, respectively. The fahrenheit scale is represented between \(32^{\circ}\) to \(212^{\circ}\).

The temperatures on two scales are related to each other by the following relationship:
\(
{ }^{\circ} \mathrm{F}=\frac{9}{5}\left({ }^{\circ} \mathrm{C}\right)+32
\)
The kelvin scale is related to celsius scale as follows:
\(
\mathrm{K}={ }^{\circ} \mathrm{C}+273.15
\)
It is interesting to note that temperature below \(0^{\circ} \mathrm{C}\) (i.e., negative values) are possible in Celsius scale but in Kelvin scale, negative temperature is not possible.