Chapter 5: Exploring Mixtures and their Separation

5.1 Classification of Mixtures

A homogeneous mixture (also called a solution) has a uniform composition throughout. Examples include sugar dissolved in water, vinegar (acetic acid in water), and aerated drinks like soda.
A heterogeneous mixture does not have a uniform composition, and its components are often visible and settle over time. Examples include sand in water, and oil in water.
We can differentiate mixtures through characteristics like particle visibility, filtration residue, and stability.

5.2 Solutions and Concentration

A solution is prepared by mixing a solute (the substance that gets dissolved) into a solvent (the substance that dissolves the solute).
The concentration of a solution refers to the amount of solute dissolved in a given amount of solvent or total solution.
Maintaining exact concentration is critical in everyday applications, such as preparing Oral Rehydration Solution (ORS) to treat dehydration or applying the correct dose of agricultural pesticides.

Mass by mass percentage (% m/m or % w/w) expresses the grams of solute present in 100 grams of the total solution. Formula: (Mass of solute / Mass of solution) × 100.
Mass by volume percentage (% m/v or % w/v) is used when measuring volumes of liquid is easier than mass (e.g., in medical saline drips, which typically contain 0.9% m/v sodium chloride). Formula: (Mass of solute / Volume of solution) × 100.
Volume by volume percentage (% v/v) is used when mixing two miscible liquids, such as vinegar or perfumes. Formula: (Volume of solute / Volume of solution) × 100.

The solubility of a substance is the maximum amount of solute that can dissolve in a fixed quantity of solvent (such as 100 g of water) at a given temperature.
A saturated solution is a solution that cannot dissolve any more solute at that specific temperature.
A solubility curve represents how solubility varies with temperature. Solubility of solid solutes generally increases with temperature, whereas the solubility of gases in liquids generally decreases as temperature rises.

5.3 Methods of Separation of Homogeneous Mixtures

A crystal is a solid whose constituent particles are arranged in a regular, geometric, repeating pattern.
Crystallization is a purification method based on solubility differences at different temperatures. It involves preparing a hot saturated solution and cooling it slowly to deposit pure crystals.
This technique is used in laboratories for purifying prepared compounds and commercially to extract pure substances like sugar and copper sulfate.

Distillation is the process of separating components of a mixture containing miscible liquids with a boiling point difference of at least 25 °C. The liquid with the lower boiling point vaporizes first, gets cooled in a condenser, and is collected as a distillate.
Fractional distillation is used when the boiling point difference between miscible liquids is less than 25 °C. This industrial process is critical in petroleum refineries to separate crude oil into fractions like gasoline, diesel, and liquefied petroleum gas (LPG).
Traditional distillation processes include India's ancient Deg-Bhapka method, used in Kannauj to extract delicate fragrances like "Mitti ka Ittar".

Paper chromatography is an analytical separation technique that relies on the different rates of movement of mixture components across a paper medium carried by a migrating solvent.
This method is widely used to separate dyes in inks, food colors, and biological pigments like green chlorophyll in leaves.

5.4 Separation of Heterogeneous Mixtures

Immiscible liquids, such as oil and water, do not mix and instead form distinct layers when left undisturbed.
A separating funnel is utilized to isolate these liquids based on their different densities, allowing the denser bottom layer to be drained off first.

Sublimation is the phase change where a solid transitions directly into a vapor state on heating without passing through an intermediate liquid state (e.g., camphor, naphthalene).
Deposition is the reverse phase change, where a cooled gas changes directly back into a solid.
An alloy is a solid-solid homogeneous mixture consisting of two or more metals, or a metal and a non-metal (e.g., brass, bronze, stainless steel). These cannot be separated into their constituents by physical means.

A suspension is a heterogeneous mixture in which insoluble solid particles (larger than 1000 nm) remain suspended in the medium and are visible to the naked eye.
Centrifugation uses rapid spinning and centrifugal force to force denser suspended particles to the bottom of a container while lighter liquids stay at the top. This is used to separate blood components (plasma and red blood cells) and in low-cost diagnostic devices like the "paperfuge".
Coagulation involves adding a chemical coagulant (like alum or fitkari) to muddy water, causing tiny suspended particles to aggregate into larger clumps and settle by gravity (sedimentation).

A colloid is a mixture with particle sizes intermediate between solutions and suspensions (1–1000 nm). The particles do not settle and are uniformly dispersed (e.g., blood, milk, cheese).
Liquid-liquid colloids are called emulsions. They are classified as oil-in-water (e.g., milk) or water-in-oil (e.g., butter) and are often stabilized by emulsifying agents like proteins.

5.5 Optical Properties of Mixtures

The Tyndall effect is the optical phenomenon of light scattering by suspended particles in a colloid or suspension, which makes the pathway of a light beam clearly visible.
Colloids consist of a dispersed phase (the solute-like particles) and a dispersion medium (the continuous solvent-like phase).
This effect explains the visibility of light beams passing through a dusty dark room, dense forest canopies, or floodlights in outdoor stadiums.