Mixtures - Notes, Chemistry | General Awareness & Knowledge - Bank Exams PDF Download

Mixtures  

Mixtures

• A material containing two or more elements or compounds in any proportion is a mixture.
• It can be separated into its constituents. e.g. air, milk, paints, cements etc.

Types of mixtures

Homogeneous

• A mixture is said to be homogeneous if its composition is uniform throughout

Heterogeneous

• A mixture is said to be Heterogeneous if its composition is not uniform.
• Properties of a mixture are the properties of its constituents.
• A mixture with definite boiling points is known as azeotropic mixture

Solutions

• A solution is a homogeneous mixture of two or more substances. For example soda water.
• we can also have solid solutions (alloys) and gaseous solutions (air).
• In a solution there is homogeneity at the particle level.
• 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.

Suspension

• 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

COLLOIDAL SOLUTION

• The particles of a colloid are uniformly spread throughout the solution. 
• Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. 
• But 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 as observed in activity 2.2. 
• This scattering of a beam of light is called the Tyndall effect after the name of the scientist who discovered this effect.

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.
• They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate the colloidal particles. 

Examples of colloids

Separation of mixture

Sublimation 

•  in this process, a solid substance passes directly into its vapours on application of heat, and when vapours are cooled, they give back the original substance, e.g iodine, naphthalene, benzoic acid etc.

Sedimentation and decantation 

• This method is used when one component is liquid and the other is insoluble solid.

Crystallization 

• This method is based on the difference in solubility of the yarious  compounds in a solvent, e.g, mixture of KNO₃ and NaCI can be separated by this process. 

Filtration

• It is used  for quick and complete removal of solid suspended particles from a liquid (or gas) by passing the suspension through a filter.

Distillation 

• A mixture of two substance, only one of which is volatile can be separated by this process, e.g,. NaCI can be separated from water by distillation.

Evaporation
 In this method the solution  is heated so that the solvent vaporises to give the solute ( solid substance ) e.g. salt can be obtained from salt solution.

Fractional distillation 

• This process is used if both the components of a mixture are volatile. It is based on the difference of boiling points e.g the various fractions of crude petroleum can be separated by this process.

Mechanical separation 

• Two immiscible liquid can be separated  by using a reparatory funnel e.g. oil and water.

Magnetic separated 

• Two solid one of which is magnetic substance can be separated by this method.