Everything in our surroundings is a form of matter. Matter is the constituents of solid, liquid and gas. Besides all these it is also a pure substance and mixture.
- A pure substance consists of a single type of particles or single form of matter with definite, invariable chemical composition and physical and chemical properties.
- A pure substance consists of homogeneous material of only one type of atoms or molecules.
- On the basis of their chemical composition, pure substance is of 2 types.
- Mixture substances are constituted by more than one kind of pure form of matter in any type of random proportion. For ex. Salt water, milk, fruit juice etc.
- A substance cannot be separated from other kinds of matter by any physical process. Example: Dissolved sodium chloride can be separated from water by the physical process of evaporation. However, sodium chloride itself is a substance and cannot be separated by physical processes into its chemical constituents. Similarly, sugar is a substance which contains only one kind of pure matter and its composition is the same throughout.
Soft drink and soil are not single pure substances.
- Whatever the source of a pure substance may be, it will always have the same characteristic properties. Therefore, we can say that a mixture contains more than one pure substance.
- PROPERTIES OF MIXTURE
- The constituents of a mixture retain their original properties because they are not chemically combined together.
- The constituents of a mixture can be separated by using a physical process such as hand picking, filtration, holding a magnet etc.
- TYPES OF MIXTURE
Depending upon the nature of the components that form a mixture, we can have different types of mixtures, but it is generally made up of 1. Homogeneous mixture and 2. Heterogeneous mixture.
- Solution is the special type of homogeneous mixture composed of two or more components which are chemically non-reacting.
- Their composition can be varied within certain limits, is called a solution.
|Solution = Solute + Solvent|
- Solute: – A substance which gets dissolved in a solvent is called a solute.
- Solvent: – A substance in which a solute gets dissolved is called a solvent.
Properties of solution
- The particles in a solution are not visible to naked eyes as its size range is less than 1nm.
- The solute particles cannot be separated from the mixture by the process of filtration.
- Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.
An alloy is considered as a mixture because it shows the properties of its constituents and can have variable. It is the mixtures of two or more metals or a metal and a non-metal and cannot be separated in to their components by physical methods.
Example, – Brass- mixture of approximately zinc (metal) and copper (metal)
Steel- mixture of iron (metal) and carbon (non-metal)
Bronze- mixture of copper (metal) and tin (metal)
- Concentration of a Solution
- The properties of a solution depend upon the nature of the solute and the solvent, and also on the proportion of the dissolved solute.
- A solution which has a high quantity of solute is said to be a concentrated solution, and a solution which has comparatively lesser quantity of solute is said to be a dilute solution.
- The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution or the amount of solute dissolved in a given mass or volume of solvent.
- Mass by mass percentage of a solution = (mass of solute÷ mass of solution) × 100
- Mass by volume percentage of a solution = (mass of solute ÷ volume of solution) × 100
- Volume by volume percentage of a solution = (volume of solute ÷ volume of solution) × 100
- Saturated Solution
At any particular temperature in a solution, in which more solute cannot be dissolved is said to be a saturated solution.
- Unsaturated Solution
At any particular temperature in a solution, in which more quantity of solute can be dissolved is called an unsaturated solution.
The maximum amount of a solute which can be dissolved in 100 grams of a solvent in a specific temperature is known as the solubility of that solute in that solvent at that temperature.
Factors affecting solubility
- Temperature– The solubility of solids in liquids is directly proportional to temperature but it is different for gases. In case of gases with the increase in temperature, they became less soluble in each other and in water, but more soluble in organic solvents.
- Pressure– The solubility of solids in liquids remains unaffected by changes in pressure. The solubility of gases in liquids is directly proportional to the pressure.
Distinguishing Properties of Solution, Suspension and Colloidal Solution
|Basis for comparison||True solution||Colloidal solution||Suspension|
|Meaning||True solutions are the type of mixtures, where the solute and solvents are properly mixed in the liquid phase.||Colloidal solutions are the type of mixture, where the solute (tiny particles or colloids) is uniformly distributed in the solvent (liquid phase).||The suspension is the mixture, where the solute does not get dissolved, rather get suspended in the liquid and float freely in the medium.|
|Example||Sugar solution in water.||Starch dissolved in water.||Soil dissolved in water.|
|Nature of the solutions||Homogenous||Heterogenous||Heterogenous|
|Size of the particles (in diameter)||<1 nm.||1-1000 nm.||>1000 nm.|
|Diffusion of the solution through parchment paper||Diffusion of the particles of the true solutions is simple and smooth through parchment and filter paper as well.||Particles of the colloidal solutions do not diffuse or pass through parchment paper, but it is easy through filter paper.||Particles of the suspension do not pass through parchment or filter paper.|
|Sedimentation||Will, not sediment.||Particles or colloids will not sediment.||Particles will get sediment.|
|Tyndall effect||The true solution does not show the Tyndall effect.||Tyndall effect is shown by the colloids in the colloidal solution.||The particles show Tyndall effect.|
|Visibility of particles||In true solutions, particles are invisible through the naked eye.||The particles in the colloidal solution are visible through the electron microscope, but not through the naked eye.||The particles in the suspension are visible through naked eyes as well as under the electron microscope.|
|Brownian Movements||Particles in the true solution do show Brownian movements.||Particles in the colloidal solution show Brownian movements.||The particles show Brownian movements.|
Tyndall effect is the scattering of light by particles in a colloid or else particle in a very fine suspension. e.g. It can be observed when sunlight passes through the canopy of a dense forest, in the forest the mist contains tiny droplets of water which act as colloidal particles dispersed in the air.
- Tyndall effect can be defined as the scattering of a beam of light by colloidal particles present in a colloidal solution.
- This effect can be observed when a fine beam of light passes through a small hole in a dark room. This effect occurs due to the scattering of light by particles of dust or smoke present in the air
Dispersed phase– The solute-like component of the dispersed particles in a colloid form the dispersed phase.
Dispersion medium– The component in which the dispersed phase is suspended is known as the dispersing medium.
Separating the Components of a Mixture
- To obtain the coloured component of a dye from blue/black ink
This method is based on the evaporation of the liquid component in a soluble solid-liquid mixture.
The mixture is heated such that the liquid component evaporates and the solid remains behind. OBSERVATION:
Ink is a mixture of a dye in water. Thus, we can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation.
- To separate Cream from Milk.
This method is based on the principle of settling down under mechanical rotation, where insoluble heavier solid particles are present in an insoluble solid-liquid mixture.
The mixture is placed in a test-tube and kept in a centrifugation machine. On centrifugation, the solid particles settle down under the influence of an outward centrifugal force and the liquid component of the mixture floats above it.
EXAMPLE- Separation of cream from milk.
- To separate a mixture of two Immiscible liquids.
This method is based on the separation of a mixture containing two immiscible liquids, containing a heavy and a light liquid.
The liquid-liquid mixture is added to the separating funnel and the funnel is allowed to stand for some time without any disturbance. The heavier immiscible liquid settles down and the lighter liquid floats above it. The two liquids can be removed separately with the help of the tap provided at the bottom of the funnel.
EXAMPLE: Separation of kerosene and water. Separation of oil and water.
- To separate a mixture of Salt and Ammonium chloride.
This method is based on the sublimable and non-sublimable nature of solids.
The mixture of a sublimable and non-sublimable substance is heated in an evaporating dish covered with an inverted funnel. This results in the evaporation of the sublimable solid and further condensation on the side of the funnel, leaving the nonsublimable solid behind in the dish.
EXAMPLE: Separation of ammonium chloride and sodium chloride in the laboratory. Separation of iodine and sodium chloride in the laboratory.
- To separate a mixture of two miscible liquids.
|Figure – distillation process|
This method is used for the separation of components of a mixture containing two miscible liquids which boil without decomposition and have a sufficient difference in their boiling points.
Take the mixture in a distillation flask and fit in the thermometer. Arrange the apparatus as shown in the given figure. Heat the mixture slowly, keeping a close watch on the thermometer. The liquid with a low boiling point will vaporise and condense in the condenser and can be collected from the condenser outlet. The liquid with a higher boiling point will be left behind in the distillation flask.
EXAMPLE: Separation of a mixture of acetone and water.
- To Separate different Components of Dye.
This method is based on the solubility of different components in solvent. The ink which we use has water as the solvent with the dye dissolved in it. As water rises on the filter paper it carries along with it the dye particles. The colour component which is more soluble in water rises faster and in this way the colours get separated.
Place a spot of ink with the help of a capillary tube in the centre of a base line, about 2-3cm away from the lower edge of a paper. Allow the spot to dry and hang it in a glass jar with its lower end immersed in the solvent.
Separation of Compound
The solvent runs over the spot and components to a distance along the paper, indicated by the coloured spots.
EXAMPLE: Different component of dyes in ink. Pigments from natural colours, Drugs from blood.
- To obtain different gases from air
This method is used for the separation of gases at different heights depending upon their boiling points.
Air is a homogeneous mixture and can be separated into its components by fractional distillation. Air is first compressed and then cooled by increasing the pressure and decreasing the temperature. Air gets liquefied. This liquid air is allowed to warm up slowly in the fractional distillation column. Gases get separated at different heights.
Flow chart and table-
|Example- to obtain different gases from air|
|Boiling point in ̊ C||-183||-186||-196|
|% of air by volume||20.9||0.9||78.1|
Figure: To obtain different gases from air.
- To Obtain Pure Copper Sulphate Crystals from An Impure Sample.
Crystallisation and Fractional Crystallisation
This method is based on the difference in the solubilities of solids in a liquid.
This method involves dissolving the mixture completely in water and heating this mixture. Further, cooling of this mixture results in the formation of crystals of a less soluble solid on the surface of the solution. Crystallisation:
The process of formation of crystals from a hot saturated solution by cooling.
The process of separation of two solids with different solubilities.
EXAMPLE: Preparation of pure copper sulphate crystals in the laboratory, Purification of salt obtained from the sea, Separation of crystals of alum from impure samples.
Purification of Drinking Water
Purification of drinking water is done in following steps-
- Water from a river or lake is brought through canals or long pipes to the water work, where it is mixed with the required quantities of alum and soda lime solutions. These substances react with one another to form aluminium hydroxide which is a jelly-like, sticky solid.
- It is then pumped into big settling tanks, where most of the suspended impurities settle down in approximate two or three days.
- The clear water is containing some suspended matter is passed through successive filters of boulders, gravel, coarse sand and fine sand. Then the clear water from the filters is chlorinated and then passed to the reservoirs for distribution in the city.
Physical and chemical changes
- If the changes occur by state of matter or substance without a change in composition and no change in the chemical nature of the substance then it is the physical changes in the substance.
For example- ice, water and water vapour all look different and display different physical properties, they are chemically the same.
- During this process of chemical changes one substance reacts with another to undergo a change in chemical composition. Chemical change brings change in the chemical properties of matter and we get new substances. A chemical change is also called a chemical reaction.
For example- burning of wood, rusting of iron
Types of pure substance
- The term element was first used by scientist Robert Boyle in 1661.
- An experimentally useful definition of an element was established by Antoine Laurent Lavoisier (1743-94), a French chemist. He defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
- Elements are divided into 3 categories as metal, metalloid, non-metal.
- Characteristics of an Element
- It is made up of a single type of atoms.
- It has a fixed melting and boiling point.
- An atom is the smallest particle of an element which takes part in a chemical reaction.
- An element can occur in the solid, liquid or gaseous state.
- Classification of elements
|Have a shiny appearance.Highest degree of metallic behaviour.Show malleability and ductility. (exception – zinc)Show high thermal and electrical conductivity. (exception- tungsten)Are solids except mercury (liquid form in room temperature)Example- Gold, silver, copper, iron, sodium, potassium||Have a dull appearance.Have less or no metallic properties.Do not show malleability and ductility. (exception- carbon)Show very low thermal and electrical conductivity. (exception – graphite)Are solid, liquid, gasExample- Solid: Carbon, silicon, phosphorous etc. Liquid: Bromine Gas: Hydrogen, chlorine etc||Have a dull or shiny appearance.Have low degree of metallic behaviour.Do not show malleability and ductility.Good conductor of electrical and thermal conductivity but less than the metal.Examples: Boron, germanium, silicon, arsenic, antimony, bismuth etc.|
A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion. The properties of compounds are different from the properties of their constituent elements. Example: H2O, CO2 etc.
- The constituents can be separated only by chemical or electro-chemical reactions.
- Molecule is the smallest part of a compound. All the molecules of a compound are similar properties to that of the compound.
- Characteristics of Compounds
- A compound has a homogeneous composition.
- Constituent particles in a compound are of one type.
- A compound is made up of one or more atoms of the same or different elements.
- In a compound the elements are present in a fixed ratio by mass.
- A compound can be divided into simpler substances by a chemical process.