Mixtures are constituted by more than one kind of pure form of matter.
For a scientist all these things are actually mixtures of different substances and hence not pure. For example, milk is actually a mixture of water, fat, proteins etc. When a scientist says that something is pure, it means that all the constituent particles of that substance are the same in their chemical nature. A pure substance consists of a single type of particles.
Whatever the source of a pure substance may be, it will always have the same characteristic properties.
Depending upon the nature of the components that form a mixture, we can have different types of mixtures.
A solution is a homogeneous mixture of two or more substances. There are various types of solutions in your daily life. Lemonade, soda water etc. are all examples of solutions.
In a solution there is homogeneity at the particle level. For example, lemonade tastes the same throughout.
A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.
Properties of a solution
A solution is a homogeneous mixture.
The particles of a solution are smaller than 1 nm (10-9 metre) in diameter. So, they cannot be seen by naked eyes.
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.
The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.
At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution. The amount of the solute present in the saturated solution at this temperature is called its solubility.
The concentration of a solution is the amount (mass or volume) of solute present in a given amount (mass or volume) of solution. There are various ways of expressing the concentration of a solution, but here we will learn only three methods.
Mass by mass percentage of a solution = Mass of solute/Mass of solution X 100
Mass by volume percentage of a solution = Mass of solute/Volume of solution X 100
Volume by volume percentage of a solution = Volume of solute/Volume of solution X 100
Non-homogeneous systems, in which solids are dispersed in liquids, are called suspensions. A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye.
Properties of a Suspension
Suspension is a heterogeneous mixture.
The particles of a suspension can be seen by the naked eye.
The particles of a suspension scatter a beam of light passing through it and make its path visible.
The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. They can be separated from the mixture by the process of filtration. When the particles settle down, the suspension breaks and it does not scatter light any more.
The particles of a colloid are uniformly spread throughout the solution. Actually, a colloidal solution is a heterogeneous mixture, for example, milk.
Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light.
Properties of a colloid
A colloid is a heterogeneous mixture.
The size of particles of a colloid is too small to be individually seen by naked eyes.
Colloids are big enough to scatter a beam of light passing through it and make its path visible.
They do not settle down when left undisturbed, that is, a colloid is quite stable.
The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.
There are different methods of separation are used to get individual components from a mixture.
Separation makes it possible to study and use the individual components of a mixture.
Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration that we use in our day-to-day life.
We find that 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.
Now-a-days, we get full-cream, toned and double-toned varieties of milk packed in polypacks or tetra packs in the market. These varieties of milk contain different amounts of fat.
Sometimes the solid particles in a liquid are very small and pass through a filter paper. For such particles the filtration technique cannot be used for separation.
Applications use to separation-:
Used in diagnostic laboratories for blood and urine tests.
Used in dairies and home to separate butter from cream.
Used in washing machines to squeeze out water from wet clothes.
The principle is that immiscible liquids separate out in layers depending on their densities.
Camphor changes directly from solid to gaseous state on heating. So, to separate such mixtures that contain a sublimable volatile component from a non-sublimable impurity, the sublimation process is used.
The ink that we use has water as the solvent and the dye is soluble in it. As the water rises on the filter paper it takes along with it the dye particles. Usually, a dye is a mixture of two or more colours. The coloured component that is more soluble in water rises faster and in this way the colours get separated. This process of separation of components of a mixture is known as chromatography.
With the advancement in technology, newer techniques of chromatography have been developed.
Applications
To separate
Colours in a dye
Pigments from natural colours
Drugs from blood.
The distillation method, we can it used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.
Air is a homogeneous mixture and can be separated into its components by fractional distillation.
To separate out all the other gases present in the air. The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air. This liquid air is allowed to warm-u slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.
The crystallisation method is used to purify solids. For example, the salt we get from sea water can have many impurities in it. Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. Crystallisation technique is better than simple evaporation technique as —
Some solids decompose or some, like sugar, may get charred on heating to dryness.
Some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid.
Applications
Purification of salt that we get from sea water.
Separation of crystals of alum (phitkari) from impure samples.
The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properites.
The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance.
Chemical change brings change in the chemical properties of matter and we get new substances. A chemical change is also called a chemical reaction.
We know that the oil burns in air whereas water extinguishes fire. It is this chemical property of oil that makes it different from water. Burning is a chemical change.
On the basis of their chemical composition, substances can be classified either as elements or compounds.
In 1661, Antoine Laurent Lavoisier (1743-94), a French chemist, was the first to establish an experimentally useful definition of an element.
An element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. Elements can be normally divided into metals, non-metals and metalloids.
Metals usually show some or all of the following properties:
They have a lustre (shine).
They have silvery-grey or golden-yellow colour.
They conduct heat and electricity.
They are ductile (can be drawn into wires).
They are malleable (can be hammered into thin sheets).
They are sonorous (make a ringing sound when hit).
Non-metals usually show some or all of the following properties:
They display a variety of colours.
They are poor conductors of heat and electricity.
They are not lustrous, sonorous or malleable.
Some elements have intermediate properties between those of metals and non-metals, they are called metalloids; examples are boron, silicon, germanium etc.
A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.