In Class 8 Science chapter 9, we explore The Amazing World of Solutes, Solvents, and Solutions as well as various factors affecting its properties.
The world around us is full of mixtures — from the air we breathe to the juice we drink. Some mixtures are uniform like saltwater, while others, such as sand and water, are not.
In this chapter, we explore how solutes dissolve in solvents to form solutions, the factors affecting solubility, and how density determines whether things float or sink. Students also learn to measure mass, volume, and density and understand how temperature and pressure influence these properties.
World of Solutes Worksheet
Our worksheets provides a wide variety of practice questions such as MCQs, fill in the blanks, true or false, and short & long answer questions. Aligned with the latest curriculum our worksheet encourages critical thinking through concept-based activities, experiments, and real-life applications.
With our engaging and well-structured worksheets, students can reinforce their classroom learning, prepare for exams, and develop a strong foundation in science.
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Science Class 8 Chapter 9 Study Notes
9.1 What Are Solute, Solvent, and Solution?
• A solution is a uniform mixture of two or more substances.
• The solute is the substance that dissolves.
• The solvent is the substance that dissolves the solute.
• Example: Salt (solute) + Water (solvent) → Salt solution.
• Air is a gaseous solution where nitrogen is the solvent and other gases are solutes.
9.2 Solubility and Types of Solutions
• The maximum amount of solute that dissolves in a fixed amount of solvent is called solubility.
• Unsaturated solution: More solute can be dissolved.
• Saturated solution: No more solute can dissolve.
• Concentration describes how much solute is present.
• Dilute solution: Less solute.
• Concentrated solution: More solute.
9.2.1 Effect of Temperature on Solubility
• For most solids, solubility increases with temperature.
• For gases, solubility decreases with temperature.
• Example: Hot water dissolves more sugar but less oxygen.
9.3 Solubility of Gases
• Oxygen dissolves slightly in water.
• Dissolved oxygen supports aquatic life.
• Cold water holds more oxygen than warm water.
9.4 Why Do Objects Float or Sink?
• Whether an object floats or sinks depends on its density.
• Less dense than water → floats
• More dense than water → sinks
9.5 Density
• Density = Mass / Volume
• Units: SI unit: kg/m³
• Common units: g/cm³ or g/ml
• Relative Density = Density of substance / Density of water
• Temperature: Increasing temperature usually decreases density.
• Pressure: Increasing pressure increases density of gases.
Effects on Density:
• Hot air balloons rise because warm air is less dense.
• Ice floats on water because it’s less dense than liquid water.
World of Solutes Question Answers
Q. Explain the effect of temperature on solubility of solids and gases.
Ans: For most solids: Solubility increases with temperature.
For gases: Solubility decreases with temperature.
Example: Oxygen dissolves more in cold water than warm water.
Q. What happens to density when temperature increases?
Ans: As temperature increases, the density of a substance generally decreases because its volume increases while mass remains constant.
Q. Differentiate between saturated and unsaturated solutions.
Ans: Saturated solution cannot dissolve any more solute; extra solute settles at the bottom. While unsaturated solution can still dissolve more solute at same temperature.