Properties of matter - Introduction
Matter is all around us. Everything in the world is made up of matter. For example, your textbook, trees, table, water, rocks, air, wind, sand
the moon and the stars are all made up of matter.
Materials are divided into metals
and non metals. Materials exist as element, compound and mixture.
The study of matter begins with the
study of its properties.
All properties of matter are either
physical or chemical properties and physical properties are either intensive or
extensive.
Extensive properties, such as mass
and volume, depend on the amount of matter being measured.
Intensive properties, such as
density and color.
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Physical properties can be measured without changing a
substance's chemical identity.
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Chemical properties can be measured only by changing a
substance's chemical identity.
Physical Properties of Matter
Matter used to make an object is
called the material. The physical properties of an object depend on the type of
material it is made from.
Now, we can focus on some of the properties
like Density, hardness, solubility, elasticity, boiling and melting point and
conductivities.
1. Density
Density
is the mass per unit volume of a substance.
Density of a material measures the amount of
matter packed in a fixed volume of the material .For eg: 1cm³ of water has a
mass of 1g. Hence, the density of water is 1 g/cm³
Understanding Density can help you predict
whether an object will float or sink.
A material that has a greater density
than water will sink, While a material less dense than water will float.
Quick check
1. A fresh egg is floating in a cup of water. You add
lots of salt to the water in the cup. How does this affect the way the egg
floats?
2. Calculate the density of an object of mass 5 N which occupies a volume of 10g/cm³. Predict whether the object will sink or float in water. Give reasons.
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2.ELASTICITY
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The ability of a material to return to
its original length or shape after stretching or bending is said to be
elasticity.
Simple example is stretching of a rubber band. When a rubber band is stretched, it becomes longer. When it is released it goes back to its original length. Hence, Rubber is and elastic material. |
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3.Hardness
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Hardness is the ability of a material
to resist scratching, wear and tear.
A harder material can be used to scratch or cut
softer material. For eg: Plasticine is softer than a pair of scissors. Thus
the pair of plastic scissors can be used to cut the plasticine.
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The MOHS scale of mineral hardness
It is a qualitative scale
that characterizes the scratch resistance of various minerals through the
ability of a harder material to scratch a softer material.
4. Solubility
Solubility is a measurement of how much of a
substance will dissolve in a given volume of a liquid.
The liquid is called the solvent. Different substances
have different solubility. The solubility of a gas depends on pressure and
temperature. In general, solids become more soluble as the temperature
increases. But gases tend to become less soluble as the temperature of the
solvent increases.
Quick Check
v Why sugar dissolves
better in hot water than in cold water.
v Fizzy drinks go ‘flat’
more quickly on a hot day than when they are stored in the fridge. Give reasons
The table shows three examples of the solubility (g of
solute per 100 g water) of substances at different temperatures.
20°C 30°C 40°C
Sodium chloride 35.9 36.1 36.4
Copper (II) sulfate 20.0 37.8 44.6
Potassium nitrate 47.0 61.6 77.0
From the table it is clear that 35.9g of NaCl salt can
dissolve in 100g of water at 20ºC. However, only 20g of CuSO4 can dissolve in
the same amount of water at same temperature.
5. Flexibility
The flexibility of a material is its ability
to bend without breaking.
For example the pole and the hose are flexible.
6. Melting point
The melting point of a substance is the
temperature at which the substance changes from solid to liquid state.
Most metals have very high melting points. If the
temperature of the substance is lower than its melting point, the substance
will be in the solid state.
The melting ice will remain at 0 °C until all of it
melts.The melting point of pure ice is 0 °C. This means that water changes from
solid ice to liquid water at 0 °C. Below its melting point, water is in the
solid state. The room temperature is about 25 °C, which is above the melting
point but below the boiling point of water. Hence, water is in the liquid state
at this temperature.
7. Boiling point
The boiling point of a substance is the
fixed temperature at which the substance changes from the liquid to the gaseous
state.
Boiling
takes place in water at 100 °C. The bubbles in the liquid are bubbles of water
vapour and not air bubbles.
When a substance boils, it changes from a liquid to
gaseous state at a fixed temperature. This fixed temperature at which a
substance boils is called its boiling point. The boiling point of water is 100
°C. Liquid water can also change to a gaseous state (water vapor) at a range of
temperatures below 100 °C. However, this process is not boiling. It is known as
evaporation.
8. Electrical conductivity
The electrical conductivity of a material is a measure
of how readily electric current flows through it. Electrical wires are usually
made of a metal called copper. This is because copper allows electric current
to flow through it easily.
A material which conducts electricity
well, such as copper, is called an electrical conductor. A material which does
not conduct electricity well is called an electrical insulator.
In general, metals are good conductors
of electricity while non-metals are insulators of electricity.
9. Thermal (heat) conductivity
The thermal (heat) conductivity of a
material is a measure of how quickly heat flows through it.
Metals allow heat to pass through them quickly. They
are good thermal (heat) conductors. Non-metals such as porcelain (a form of
ceramics) and plastics do not conduct heat well. They are known as thermal
(heat) insulators.
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