All matter has physical and chemical properties. Extensive properties are those properties of a substance which depend on the amount of substance. They vary with the amount of the substance. Examples: Mass, weight, and volume. Intensive properties are those properties of a substance which do not depend on the amount of substance. Examples: colour, melting point, boiling point, electrical conductivity, and physical state at a given temperature.

Physical Properties of Substance:

Physical properties are characteristics that can be measured or observed without changing the composition of the substance under study. All samples of a pure substance have the same chemical and physical properties. Physical properties can be extensive or intensive. 

Mass

A mass is the amount of matter that is found in a substance. Mass is expressed in terms of kilograms (kg).

Density

Density is the measurement of mass with respect to and in a relationship with volume. The mass of a substance per its unit volume is called density. Density is expressed in kilograms per cubic metre (kg/m³). Mathematically

Density = Mass / Volume

The density depends on the temperature and pressure of the substance. The effect is prominent in cases of gases. The application of increasing temperature decreases its density because its volume increases with increasing temperatures, and the application of increasing pressure increases density because the volume decreases with increasing pressure.

Volume

Volume is the measurement of the quantity or amount of matter in a three dimensional space. It is the space occupied by the substance. Volume is expressed in cubic metres (m³).

Boiling Point:

The temperature at which a liquid changes its state to a gas at atmospheric pressure is called the boiling point of that liquid.  It is defined as the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure. This is the point at which both liquid and gaseous phase exists at equilibrium. The boiling point of the substance also varies with pressure and is specified at standard pressure.

The boiling point of a liquid is a characteristic property and can be treated as a criterion for the purity of liquid.  It increases with the increase in external pressure. Liquids having greater intermolecular forces have high boiling points.

Melting Point:

The temperature at which a solid changes its state to a liquid at atmospheric pressure is called the melting point of that solid. This is the point at which both liquid and solid phase exists at equilibrium. The melting point of the substance also varies with pressure and is specified at standard pressure.

The melting point of a liquid is a characteristic property and can be treated as a criterion for the purity of a solid.  It increases with the increase in external pressure. Solids having greater intermolecular forces have high melting points.

Conductivity

Conductivity is the measure of a substance’s ability, or lack of ability, to conduct electricity or heat. Some matter has a high level of conductivity and other matter has a high level of resistance to the conduction of electricity.

Heat Capacity

Simply stated, heat capacity is the amount of heat that must be added or taken away from a substance to achieve a certain temperature. Heat capacity is also referred to as thermal capacity and the amount of heat that is added or taken away is measured in terms of joules per kelvin.

Deliquescence:

Deliquescence refers to the property of a substance to absorb water from the air to dissolve itself and form an aqueous solution. Materials showing deliquescence are termed deliquescent. In order to be deliquescent, a substance must both absorb a large amount of water and be sufficiently soluble to dissolve in it. Examples: Sodium hydroxide, potassium hydroxide, anhydrous potassium chloride, anhydrous magnesium chloride, anhydrous ferric chloride show deliquescence.

Hygroscopicity:

Hygroscopicity is the tendency of a solid substance to absorb moisture from the surrounding atmosphere and are converted into hydroxides or hydrates. Anhydrous copper sulphate, quick lime (CaO), anhydrous sodium carbonate, etc. are hygroscopic in nature.

Efflorescence:

Efflorescence is a spontaneous loss of water by a hydrated salt, which occurs when the aqueous vapor pressure of the hydrate is greater than the partial pressure of the water vapour in the air. Washing soda (Na₂CO₃·10H₂O), Glauber’s salt or sodium sulphate (Na₂SO₄·10H₂O), Ferrous sulphate (FeSO₄·7H₂O), potash alum (K₂SO₄· Al₂(SO₄)₃.24H₂O) show efflorescence.

Mechanical Properties of Substance:

Strength:

It is the property of a material which opposes the deformation or breakdown of material in presence of external forces or load. Engineering materials must have the suitable mechanical strength to be capable to work under different mechanical forces or loads. It is shown by solids.

Toughness:

Toughness is the ability of a material to absorb energy and gets plastically deformed without fracturing. For good toughness, materials should have good strength as well as ductility. To be tough, the material should be capable to withstand both high stress and strain. It is shown by solids.

Elasticity:

Within elastic limit, the solid completely regains its original shape, size or volume after removal of deforming force, then the property is called elasticity. Steel, copper, aluminium show elastic behaviour.

Plasticity:

If a body is stressed beyond elastic limit, and it does not regain original shape, size, and volume after removal of deforming force, then the property is called plasticity. These substances can be given required shape very easily. Example: Plaster of paris

Hardness:

It is the ability of a material to resist permanent shape change due to external stress. There are various measures of hardness – Scratch Hardness, Indentation Hardness, and Rebound Hardness. Scratch Hardness is the ability of materials to oppose the scratches to the outer surface layer due to external force. It is shown by solids.

It is measured on Mohs’ scale. The Mohs’ scale of mineral hardness is a qualitative ordinal scale that characterizes the scratch resistance of different minerals through the ability of a harder material to scratch a softer material. It was created by the German geologist and mineralogist Friedrich Mohs in 1812.

On Moh’s scale hardness of a diamond is maximum (10) and that of talk is minimum (1). If a material can scratch topaz but can’t scratch corundum, then it possesses hardness equal to 8.

Brittleness:

The brittleness of a material indicates that how easily it gets fractured when it is subjected to a force or load. The solids of non-metal are generally brittle in nature. The brittleness of the material is temperature-dependent. Some metals which are ductile at normal temperature become brittle at low temperature. Hardness and brittleness are inverse properties. The harder the substance, the more brittle it is. It is shown by solids.

Malleability:

Malleability is a property of solid materials which indicates that how easily a material gets deformed under compressive stress. Malleability is often categorized by the ability of the material to be formed in the form of a thin sheet by hammering or rolling. This mechanical property is an aspect of the plasticity of the material. The malleability of material is temperature-dependent. With the rise in temperature, the malleability of material increases. This is the characteristic property of metals. Copper, aluminium, gold, silver show malleability. Gold is the most malleable metal.

Ductility:

Ductility is a property of a solid material indicates that how easily a material gets deformed under tensile stress. Ductility is often categorized by the ability of a material to get stretched into a wire by pulling or drawing. This mechanical property is also an aspect of the plasticity of material and is temperature-dependent. With the rise in temperature, the ductility of material increases. This is a characteristic property of metals. Copper, aluminium, gold, silver show ductility. Platinum is the most ductile metal.

Creep:

Creep is the property of a material that indicates the tendency of a material to move slowly and deform permanently under the influence of external mechanical stress. It results due to long time exposure to large external mechanical stress within the limit of yielding. Creep is more severe in materials that are subjected to heat for a long time.

Resilience:

Resilience is the ability of material to absorb the energy when it is deformed elastically by applying stress and release the energy when stress is removed. Proof resilience is defined as the maximum energy that can be absorbed without permanent deformation. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without permanent deformation.

Fatigue:

Fatigue is the weakening of a material caused by the repeated loading of the material. When a material is subjected to cyclic loading, and loading greater than a certain threshold value but much below the strength of the material (ultimate tensile strength limit or yield stress limit), microscopic cracks begin to form at grain boundaries and interfaces. Eventually, the crack reaches a critical size. This crack propagates suddenly and the structure gets fractured.

Chemical Properties of Substance:

Chemical properties are characteristics that can only be measured or observed as matter transforms into a particular type of matter. The tendency of matter to react chemically with other substances is known as reactivity.

Reactivity:

The tendency of matter to combine chemically with other substances is known as reactivity. Certain materials like chlorine, potassium, sodium, etc. are highly reactive, whereas others like gold, platinum, etc. are extremely inactive.

Flammability:

The tendency of matter to burn is referred to as flammability. As matter burns, it reacts with oxygen and transforms into various substances. Example: wood, paper, etc. are flammable. Petrol, ethyl alcohol are highly flammable.

Toxicity:

Toxicity refers to the extent to which a chemical element or a combination of chemicals may harm an organism. Methyl alcohol, methyl isocyanate are highly toxic.

Reactivity with Acids and Bases:

A substance’s ability to react with an acid or a base is a chemical property.

Science > Chemistry > Introduction to Chemistry > Properties of Substance

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In this article, we shall study the measurement of the density of a substance.

Eureka! Eureka!

Archimedes was a Greek scientist. He lives in Syracuse nearly 200 years ago. The King of the land wanted to wear a Golden Crown. He gave some gold to a goldsmith to make a suitable crown. After a few days, the goldsmith brought the finished crown to the King. The crown was weighed. The weight of the crown was equal to the gold given to the goldsmith by the King. The King looked at the color of the crown. He had a suspicion. The goldsmith could have stolen some gold from the gold given to him. The King wanted to find out the truth. He asked his court scientist Archimedes to find out. The King said, “Find out how much gold had been stolen?”

How to find out the truth? Archimedes thought about the problem day and night. One day he was about to have his bath, but he was busy thinking. He did not notice the bathtub. The water in the bathtub was already full to the brim. He slid into the bathtub. Immediately a large quantity of water flowed over the brim of the bathtub. He noticed this suddenly. His brain wave worked suddenly. He jumped out of the bathtub, shouting, “Eureka! Eureka!” Eureka in Greek means “I have found it.” He proposed different metals of the same weight have different volumes. Objects, put in water, will displace water. The displaced water will be equal to their volume.

Archimedes took two bowls. He filled them with water to the brim. Then he placed each bowl separately in the middle of the large vessels. He placed the crown in one bowl. Water overflowed. It collected at the bottom of the outer vessel. Then he took a cube of pure gold. This cube of gold was equal in weight to the crown. He kept this gold cube in the middle of the second bowl. Here also water overflowed. Water got collected at the bottom of the outer bowl.

Archimedes then measured the quantity of water in the two vessels. He found out the difference in the water overflow. The crown had sent out more water. The cube of gold had sent out less water. But both the crown and the gold cube were of the same weight. So, they should have sent out the same quantity of water. Therefore, the crown had some other metals mixed in it. These metals took up more space in the water than pure gold.

Archimedes reported this finding to the King. The King demanded the truth from the goldsmith. The goldsmith then confessed. He had stolen some gold. He had added some other metals.

The Concept of Density:

Two substances having the same mass can occupy different volumes due to the difference in their densities or two substances having the same volume can have different masses. For example oil (density 800 kg/ m³) and water (density (1000 kg/ m³ ) have different densities, hence 1000 kg of oil occupies 1.250 m³ while 1000 kg of water occupies 1 m³. Similarly, 1 m³ of oil has mass 800 kg, while 1 m³ of water has mass 1000 kg. This behavior can be explained on the basis of the kinetic molecular theory. According to this theory, either of the following explanation is true.

• Perhaps the individual particles of oil and water each have the same mass, but in water, the particles are closely packed than those in oil. or
• Perhaps the individual particles of oil and water are equally spaced, but particles of water have more mass than those of the oil.

The property of matter that describes the relationship between mass and volume is called density. The density of a substance is defined as the mass of the substance per unit volume. It is denoted by letter’ or symbol (ρ) rho.

Mathematically.

Density = Mass/Volume

Its S.I. unit is kg m^-3, c.g.s. unit is g cm^-3. Sometimes the density of a liquid is expressed in g/litre.

Effect of Temperature on Density:

Most of the substances expand on heating and contract on cooling but their mass remains unchanged. Thus the density of substance decreases with an increase in temperature and it increases with a decrease in temperature.

But water below 4 ^oC behaves differently. When water is cooled below 4 ^oC water expands. Hence when water is cooled up to 4 ^oC, its density increases but below 4 ^oC it increases. This behaviour of water is called anomalous behaviour. Thus water has a maximum density at 4 ^oC.

Effect of Change of State on Density:

If the physical state of substance changes its density changes. For water (liquid) it is 1000 kg/ m³, for ice (solid) it is 900 kg/ m³ and for steam (gas) it is 0.59 kg/ m³ .

Factors Affecting Density:

• The space between particles of the substance
• The mass of the particle of the substance
• The temperature of the substance

Density of Mixture:

Numerical Problems:

Example – 01:

Mass of 2 m³ block of ice is 1800 kg. Find its density.

Given: Volume = V = 2 m³, Mass = M = 1800 kg

Solution:

Density = Mass/Volume = 1800/2 = 900 kg m^-3

Ans: The density of ice is 900 kg m^-3

Example – 02:

Mass of a block having length, breadth, and height 6 cm, 3 cm, and 2 cm respectively is 550.8 g. Find its density

Given: Length = 6 cm, breadth = 3 cm, height = 2 cm, Mass = M = 550.8 g

Solution:

Volume of block = length x breadth x height = 6 x 3 x 2 = 36 cm³

Density = Mass/Volume = 550.8/36 = 15.3 g cm^-3

Ans: The density of material of block is 15.3 g cm^-3

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