Chemistry Keypoints; Separation of mixtures and purification of chemical substances; Chemistry involves the study of matter and its properties. Matter is anything that has mass and occupies space. Matter can be classified as either a pure substance or a mixture. A pure substance is made up of only one type of particle, while a mixture is made up of two or more different types of particles.
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Chemistry Keypoints; Separation of mixtures and purification of chemical substances
(a) Pure and Impure Substances
A pure substance is a substance that consists of only one type of particle. A pure substance can be an element or a compound. An element is a substance that cannot be broken down into simpler substances, while a compound is a substance made up of two or more different elements. An impure substance, also known as a mixture, is a substance made up of two or more different types of particles.
(b) Boiling and Melting Points
Boiling and melting points are important criteria for the purity of chemical substances. A pure substance will have a definite boiling and melting point, while an impure substance will have a range of boiling and melting points. The boiling point of a substance is the temperature at which it changes from a liquid to a gas, while the melting point is the temperature at which it changes from a solid to a liquid.
(c) Elements, Compounds, and Mixtures
An element is a substance that cannot be broken down into simpler substances. It is made up of only one type of atom. A compound is a substance made up of two or more different elements that are chemically combined. A mixture is made up of two or more different types of particles that are physically combined.
(d) Chemical and Physical Changes
A chemical change is a change in which one or more new substances are formed. Chemical changes involve the breaking and forming of chemical bonds. A physical change, on the other hand, is a change in which no new substances are formed. Physical changes involve changes in the physical state of matter, such as melting, boiling, or freezing.
(e) Separation Processes
There are various methods for separating mixtures into their individual components. These include:
- Evaporation: This method involves heating a liquid to evaporate it and leaving behind any solid impurities.
- Simple and Fractional Distillation: This method is used to separate liquids that have different boiling points. Simple distillation is used for separating liquids with a large difference in boiling points, while fractional distillation is used for liquids with smaller differences in boiling points.
- Sublimation: This method is used to separate a solid from a mixture of solids by heating the mixture, causing the solid to vaporize and then condense back into a solid.
- Filtration: This method involves passing a mixture through a filter to separate a solid from a liquid.
- Crystallization: This method is used to separate a solid from a solution by cooling the solution, causing the solid to form crystals.
- Paper and Column Chromatography: This method is used to separate a mixture of different compounds based on their ability to move through a stationary phase. The stationary phase can be paper or a column filled with a specific material.
- Simple and Fractional Crystallization: This method is used to separate a mixture of solids based on their solubility in a specific solvent. Simple crystallization is used for solids with large differences in solubility, while fractional crystallization is used for solids with smaller differences in solubility.
- Magnetization: This method is used to separate a mixture of solids based on their magnetic properties.
- Decantation: This method involves pouring off a liquid from a solid that has settled to the bottom of a container.
Objectives
(i) Distinguishing between Pure and Impure Substances
A pure substance is a substance that is made up of only one type of particle, either an element or a compound. An impure substance, on the other hand, is made up of two or more different types of particles. Pure substances have a uniform composition throughout, whereas impure substances have a non-uniform composition. The properties of pure substances are constant, while the properties of impure substances can vary.
(ii) Using Boiling and Melting Points as Criteria for Purity
Boiling and melting points are important criteria for determining the purity of a substance. A pure substance will have a sharp and specific melting or boiling point, whereas an impure substance will have a melting or boiling point range. The presence of impurities in a substance can lower the melting or boiling point and broaden the range.
(iii) Distinguishing Between Elements, Compounds, and Mixtures
An element is a substance that is made up of only one type of atom. It cannot be broken down into simpler substances by chemical means. A compound is a substance that is made up of two or more different types of atoms that are chemically bonded together. It can be broken down into simpler substances by chemical means. A mixture is a substance made up of two or more different types of particles that are physically combined. Mixtures can be homogeneous or heterogeneous.
(iv) Differentiating Between Chemical and Physical Changes
A physical change is a change in which the substance undergoes a change in physical state or appearance but its chemical identity remains the same. Examples of physical changes include melting, freezing, boiling, and evaporation. A chemical change, on the other hand, is a change in which the substance undergoes a change in chemical composition resulting in the formation of one or more new substances. Examples of chemical changes include combustion, oxidation, and decomposition.
(v) Identifying the Properties of the Components of a Mixture
The properties of the components of a mixture can be different from each other. For example, a mixture of sand and iron filings can be separated using a magnet because iron is magnetic while sand is not. Similarly, a mixture of oil and water can be separated using the difference in their densities as oil is less dense than water.
(vi) Specifying the Principle Involved in Each Separation Method
Each separation method is based on a specific principle. For example, distillation is based on the difference in boiling points of the components of a mixture. Filtration is based on the difference in particle size between the components of a mixture. Chromatography is based on the difference in solubility or adsorption properties of the components of a mixture.
(vii) Applying the Basic Principle of Separation Processes in Everyday Life
Separation processes are used in various industries and everyday life. For example, the distillation process is used in the purification of water and the separation of crude oil into its various components. Filtration is used in the purification of air and water, and in the separation of solids from liquids. Chromatography is used in the separation and analysis of various compounds in the pharmaceutical and chemical industries.
