This chapter explains how different substances mix to form solutions and why some mixtures appear uniform while others do not. It introduces the concepts of solute, solvent, and solution using everyday examples like sugar in water and ORS. The chapter also explores how much solute a solvent can dissolve, how temperature affects solubility, and how gases dissolve in liquids. Further, it explains why some objects float or sink by introducing the idea of density, along with methods to measure mass and volume accurately. Through simple activities and real-life connections, the chapter helps students understand the science behind mixing, dissolving, floating, and sinking.
Key Points
A uniform mixture is called a solution.
The substance that dissolves is the solute, and the substance that dissolves it is the solvent.
In a solution, components are evenly distributed and cannot be seen separately.
Air is a solution of gases where nitrogen acts as the solvent.
A solution that can dissolve more solute is called an unsaturated solution.
A solution that cannot dissolve more solute at a given temperature is a saturated solution.
Solubility is the maximum amount of solute that can dissolve in a fixed amount of solvent at a given temperature.
Solubility of most solids increases with increase in temperature.
Solubility of gases decreases when temperature increases.
Oxygen dissolved in water supports aquatic life.
Objects float or sink based mainly on their density.
Density = Mass ÷ Volume.
Density is independent of shape but depends on temperature and pressure.
Heating generally decreases density, while cooling increases it.
Ice floats on water because it is less dense than liquid water.
👉 👉Understanding solutions and density helps us explain many everyday phenomena—from making ORS to why ships float and ice forms on lakes. Scientific thinking allows us to observe carefully, measure accurately, and apply knowledge responsibly in daily life and environmental care.