Chapter 2: Is Matter Around Us Pure? – Summary
This chapter explores the concept of pure substances and mixtures and helps differentiate between them.
1. Pure Substances
• A pure substance contains only one kind of particle.
• It can be an element (like iron, oxygen) or a compound (like water, carbon dioxide).
2. Mixtures
• A mixture contains two or more substances (elements or compounds) that are physically combined.
• Mixtures can be homogeneous (uniform composition, like salt in water) or heterogeneous (non-uniform, like oil in water).
3. Types of Mixtures
• Solutions: Homogeneous mixtures (e.g., sugar in water). Components cannot be seen separately.
• Suspensions: Heterogeneous mixtures where particles settle down (e.g., sand in water).
• Colloids: Intermediate mixtures where particles don’t settle (e.g., milk, fog).
4. Separation of Mixtures
Different techniques are used based on the type of mixture:
• Evaporation
• Centrifugation
• Filtration
• Sublimation
• Chromatography
• Distillation (simple and fractional)
5. Physical and Chemical Changes
• Physical changes do not alter the chemical composition (e.g., melting ice).
• Chemical changes result in new substances (e.g., rusting iron).
6. Elements, Compounds, and Mixtures
• Element: Made of one type of atom (e.g., hydrogen).
• Compound: Made of two or more elements chemically combined in a fixed ratio (e.g., H₂O).
• Mixture: Two or more substances mixed physically in any proportion.
Separation of Mixtures
1. Evaporation
Definition:
Used to separate a soluble solid from a liquid by heating the mixture until the liquid evaporates, leaving the solid behind.
Example:
Separating salt from saltwater.
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2. Centrifugation
Definition:
A method used to separate denser particles from lighter particles in a liquid by spinning the mixture at high speed.
Example:
Separating cream from milk.
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3. Filtration
Definition:
Used to separate insoluble solids from a liquid using a filter paper or mesh.
Example:
Separating sand from muddy water.
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4. Sublimation
Definition:
A technique to separate a sublimable solid (that changes directly into gas on heating) from a mixture.
Example:
Separating ammonium chloride from salt.
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5. Chromatography
Definition:
A method used to separate different components of a mixture based on how well they travel with a solvent on a given surface.
Example:
Separating dyes in black ink using paper chromatography.
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6. Distillation
Definition:
Used to separate miscible liquids with different boiling points by heating the mixture and condensing the vapour.
Example:
Separating acetone from water.
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7. Fractional Distillation
Definition:
A refined form of distillation used to separate a mixture of two or more miscible liquids with closely related boiling points.
Example:
Separating different gases from air (like oxygen and nitrogen).
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