Chapter Overview
1 g/mL
Density of Water
4 °C
Max Density of Water
2.7 g/cm³
Density of Aluminium
0 °C
Freezing Point of Water
What You'll Learn
Solutes, Solvents, Solutions
Understanding mixtures, uniform vs. non-uniform, and components of solutions.
Solubility and Saturation
Exploring how much solute dissolves and effects of temperature.
Density and Buoyancy
Learning why objects float or sink, measuring mass and volume.
Effects on Density
Temperature and pressure impacts on matter states.
Key Highlights
This chapter explores solutions like ORS, where solutes (sugar, salt) dissolve in solvent (water) uniformly. It covers saturation, solubility's temperature dependence, gas solubility, and density's role in floating/sinking. Activities demonstrate concepts like dissolving baking soda and measuring volumes.
Comprehensive Chapter Summary
9.1 What Are Solute, Solvent, and Solution?
A solution is a uniform mixture where components are evenly distributed, like sugar and salt in water for ORS. Solute is the dissolved substance (e.g., salt), solvent is the dissolver (e.g., water). Air is a gaseous solution with nitrogen as solvent.
9.2 How Much Solute Can a Fixed Amount of Solvent Dissolve?
Unsaturated vs. Saturated
Unsaturated solutions can dissolve more solute; saturated cannot at given temperature. Concentration: dilute (less solute) vs. concentrated (more).
Solubility
Maximum solute in fixed solvent quantity at specific temperature.
9.2.1 How does temperature affect the solubility of a solute?
Solubility of solids increases with temperature; e.g., more baking soda dissolves at higher temperatures. Saturated at one temperature becomes unsaturated when heated.
9.3 Solubility of Gases
Gases in Water
Oxygen dissolves slightly in water, sustaining aquatic life. Solubility decreases with temperature increase.
9.4 Why Do Objects Float or Sink in Water?
Floating and Sinking
Depends on density; less dense objects float (e.g., wood), denser sink (e.g., iron).
9.5 What Is Density?
Density = mass/volume. Independent of shape/size, but depends on temperature/pressure. Units: kg/m³, g/cm³.
9.5.1 Determination of density
Measure mass with balance, volume with cylinder (regular: l×w×h; irregular: displacement).
9.5.2 Effect of temperature on density
Generally decreases with heating due to expansion. Water max density at 4°C; ice floats as less dense.
9.5.3 Effect of pressure on density
Increases for gases (compression); negligible for liquids/solids.
Questions and Answers from Chapter
Short Questions
Q1. What is a solution?
Answer: A uniform mixture where components are evenly distributed.
Q2. Define solute.
Answer: The solid or lesser component that dissolves in the solvent.
Q3. What is solvent?
Answer: The liquid or greater component that dissolves the solute.
Q4. What is an unsaturated solution?
Answer: A solution that can dissolve more solute at a given temperature.
Q5. Define saturated solution.
Answer: A solution where no more solute can dissolve at that temperature.
Q6. What is solubility?
Answer: Maximum amount of solute in fixed solvent at a temperature.
Q7. How does temperature affect solid solubility?
Answer: Increases with temperature rise.
Q8. How does temperature affect gas solubility?
Answer: Decreases with temperature rise.
Q9. What is density?
Answer: Mass per unit volume.
Q10. SI unit of density?
Answer: kg/m³.
Q11. What is mass?
Answer: Quantity of matter in an object.
Q12. What is volume?
Answer: Space occupied by an object.
Q13. How to measure irregular volume?
Answer: Water displacement method.
Q14. Effect of temperature on density?
Answer: Generally decreases.
Q15. Why does ice float?
Answer: Less dense than water.
Medium Questions
Q1. Why are mixtures like salt in water uniform?
Answer: Components evenly distributed, forming a solution where solute dissolves in solvent. E.g., ORS tastes same every sip. (3 marks)
Q2. Differentiate dilute and concentrated solutions.
Answer: Dilute has less solute; concentrated has more in fixed solution quantity. Relative terms. (3 marks)
Q3. How does heating affect baking soda solubility?
Answer: More dissolves at higher temperatures like 50°C or 70°C than 20°C. (3 marks)
Q4. Why is air a solution?
Answer: Gaseous mixture; nitrogen solvent, oxygen/others solutes. (3 marks)
Q5. Explain gas solubility in water.
Answer: Oxygen dissolves slightly, sustains aquatic life; decreases with warmth. (3 marks)
Q6. Why do some objects float?
Answer: Less dense than water, like wood vs. iron. (3 marks)
Q7. Define relative density.
Answer: Density of substance divided by water's density; unitless. (3 marks)
Q8. How to measure mass?
Answer: Use digital balance; tare, place object, read. (3 marks)
Q9. What is meniscus?
Answer: Curved liquid surface in cylinder; read bottom for water. (3 marks)
Q10. Volume of regular shapes?
Answer: Length × width × height for cuboids. (3 marks)
Q11. Why narrow measuring cylinders?
Answer: Better accuracy for small volumes. (3 marks)
Q12. Effect of pressure on gases?
Answer: Increases density by compression. (3 marks)
Q13. Why ice floats on water?
Answer: Expands, less dense at 0°C than water at 4°C. (3 marks)
Q14. Units of volume?
Answer: m³, dm³ (L), cm³ (mL). (3 marks)
Q15. What is concentration?
Answer: Solute amount in fixed solution/solvent. (3 marks)
Long Questions
Q1. Explain solute, solvent, and solution with examples.
Answer: A solution is uniform mixture, e.g., salt/sugar in water. Solute: dissolved solid (salt). Solvent: dissolving liquid (water). In liquids mix, lesser is solute, greater solvent. Air: nitrogen solvent, others solutes. Gulab jamun syrup: sugar solute, water solvent despite amounts.
Q2. Describe saturated and unsaturated solutions.
Answer: Unsaturated: more solute can dissolve at temperature. Saturated: no more dissolves, undissolved settles. From activity: initial salt dissolves (unsaturated), later settles (saturated). Concentration: dilute (less solute), concentrated (more).
Q3. How temperature affects solubility?
Answer: For solids, increases; e.g., baking soda more at 70°C than 20°C. Saturated becomes unsaturated on heating. Gases: decreases; more oxygen in cold water.
Q4. Discuss density and its determination.
Answer: Density = mass/volume. Measure mass with balance: tare, place object. Volume: regular l×w×h; irregular displacement. E.g., stone 16.4g, 5cm³ displaces, density 3.28g/cm³.
Q5. Why objects float or sink?
Answer: Based on density vs. water. Less dense float (wood), denser sink (iron). Not just weight; density key. E.g., husk floats, rice sinks in water.
Q6. Effects of temperature and pressure on density.
Answer: Temperature: decreases density (expansion). Water anomaly: max at 4°C, ice less dense. Pressure: increases gas density; negligible liquids/solids.
Q7. Explain measuring volume with cylinder.
Answer: Pour to mark, adjust with dropper. Read meniscus bottom for clear liquids. Capacities vary; smaller for accuracy. E.g., 100mL reads 1mL smallest.
Q8. What is relative density?
Answer: Substance density / water density; unitless. E.g., aluminium 2.7 means 2.7 times denser than water.
Q9. Describe activity on salt dissolution.
Answer: Add salt spoons to water tumbler, stir. Dissolves initially, then settles. Indicates water's capacity limit, reaching saturation.
Q10. Why ice floats and its importance.
Answer: Ice less dense due to expansion at 0°C. Floats, insulates water below, sustains aquatic life in cold.
Q11. Explain mass vs. weight.
Answer: Mass: matter quantity (g/kg). Weight: gravitational force (N). Balances measure weight but scaled in mass.
Q12. How to find irregular volume?
Answer: Immerse in water, measure displacement. E.g., stone: 50mL to 55mL = 5cm³.
Q13. Units and conversions for density.
Answer: kg/m³, g/cm³. 1 kg/m³ = 1 g/L. Water ~1g/mL.
Q14. Describe baking soda experiment.
Answer: Add to water at 20°C till saturated, heat to 50°C/70°C, more dissolves showing temperature effect.
Q15. Why water good solvent?
Answer: Dissolves many like sugar/salt, not oil. Used in medicines, Ayurveda.
