When we drink ORS or mix sugar in our tea, we are actually witnessing the science of solutes, solvents and solutions in action. The uniform taste throughout every sip shows us how substances can completely blend together at the microscopic level.
What Are Solute, Solvent, and Solution?
When you add salt or sugar to water, they form a uniform mixture where the components are evenly distributed throughout. This is what we call a solution. In any solution, we can identify two main components based on their roles in the mixing process.
Understanding Basic Terms
Solute – The substance that gets dissolved in the solution. When you add salt to water, salt is the solute.
Solvent – The substance that does the dissolving. Water acts as the solvent when salt dissolves in it.
Solution – The uniform mixture formed when solute completely dissolves in solvent.
The simple equation for this process is: Solute + Solvent = Solution
Identifying Solute and Solvent
When a solid dissolves in a liquid, it’s easy to identify – the solid is always the solute and the liquid is the solvent. But when two liquids mix, we need to look at quantities. The substance present in smaller amount becomes the solute, while the one in larger amount acts as the solvent.
Example from Indian Cuisine
The chashni (sugar syrup) for Gulab jamun contains a large amount of sugar dissolved in a small amount of water. Even though there’s more sugar than water, water is still considered the solvent because it’s doing the dissolving work, and sugar is the solute.
Air as a Solution
Air around us is actually a gaseous solution. Since nitrogen makes up about 78% of air, it acts as the solvent. Oxygen, argon, carbon dioxide, and other gases present in smaller quantities act as solutes. This shows us that solutions can exist in gaseous state too, not just as liquids.
How Much Solute Can a Fixed Amount of Solvent Dissolve?
Every solvent has a limit to how much solute it can dissolve at a given temperature. This limit helps us understand different types of solutions and how concentration affects their properties.
Types of Solutions Based on Solute Amount
Unsaturated Solution
- More solute can still be dissolved at that temperature
- Solution has not reached its dissolving capacity
- Additional solute will completely dissolve when added
Saturated Solution
- Maximum amount of solute has been dissolved at that temperature
- No more solute can dissolve; extra solute settles at the bottom
- Solution has reached its dissolving limit
Concentration
The amount of solute present in a fixed quantity of solution is called concentration. Solutions can be:
- Dilute solution – Contains less amount of solute
- Concentrated solution – Contains more amount of solute
These are relative terms, meaning they depend on comparison. A solution with 1 spoon of salt is dilute compared to one with 3 spoons of salt.
Understanding Solubility
Solubility is the maximum amount of solute that dissolves in a fixed quantity of solvent at a particular temperature. Different substances have different solubility limits in the same solvent.
How does temperature affect the solubility of a solute?
Temperature plays a crucial role in determining how much solute can dissolve in a solvent. Understanding this relationship helps explain many everyday phenomena.
Effect of Temperature on Solid Solutes
For most solid substances, solubility increases with increase in temperature. This means:
- Hot water can dissolve more sugar than cold water
- A saturated solution at room temperature becomes unsaturated when heated
- Higher temperature provides more energy to break bonds and dissolve solute particles
Practical Example
When you heat water containing undissolved baking soda, the extra baking soda starts dissolving. As temperature increases from 20°C to 50°C to 70°C, more and more baking soda can dissolve in the same amount of water.
Scientific Heritage in Medicine
Traditional Indian medicine systems like Ayurveda and Siddha have used the principle of solubility for centuries:
- Water has been the primary solvent for medicinal formulations
- Hydro-alcoholic extracts were prepared for better extraction
- Oils, ghee, and milk were used as specialized solvents
- Different solvents helped achieve specific therapeutic benefits
Asima Chatterjee’s Contribution
Dr. Asima Chatterjee, a renowned Indian chemist, extensively used solvents and solutions to extract compounds from medicinal plants. She developed anti-epileptic and anti-malarial drugs and became the first woman to receive the Shanti Swarup Bhatnagar Award in chemical sciences.
Solubility of Gases
Gases can also dissolve in liquids, though their behavior is quite different from solid solutes. This dissolved gas plays imp roles in sustaining life and various industrial processes.
Gas-Liquid Solutions
Oxygen in Water
- Oxygen dissolves in water to a small extent
- This dissolved oxygen is essential for aquatic life
- Fish and other aquatic organisms depend on this dissolved oxygen for survival
- Without dissolved oxygen, aquatic ecosystems would collapse
Temperature Effect on Gas Solubility
Unlike solid solutes, gas solubility generally decreases as temperature increases:
- Cold water can dissolve more oxygen than hot water
- This is why aquatic life thrives better in cooler waters
- Global warming affects oxygen levels in water bodies
- Industrial cooling can reduce dissolved oxygen in rivers
Uniform vs Non-Uniform Mixtures
When gases dissolve in liquids, they form uniform mixtures because gas particles distribute evenly throughout the liquid. This is why dissolved gases form true solutions rather than just mixtures.
Why Do Objects Float or Sink in Water?
The behavior of objects in water depends on their density relative to water. Understanding density helps explain many phenomena we observe in daily life.
Observable Phenomena
Common Observations
- Rice sinks while rice husk floats during washing
- Oil floats on water surface
- Some objects like wood float while others like iron sink
- Ice floats on liquid water
Introduction to Density
Density describes how much matter is packed into a given space. It’s a property that determines whether objects will float or sink in liquids.
Everyday Examples
- A crowded bus has high density of people
- A bus with few passengers has low density
- Dense forest has trees growing close together
- Less dense forest has trees spread far apart
What Is Density?
Density is defined as the mass present in a unit volume of a substance. It’s an intrinsic property that doesn’t change with the size or shape of an object.
Mathematical Definition
Formula: Density = Mass ÷ Volume
The density of a substance is independent of its shape or size but depends on temperature and pressure. This makes it a characteristic property useful for identifying substances.
Units of Density
SI Units
- Mass: kilogram (kg)
- Volume: cubic meter (m³)
- Density: kg/m³
Practical Units
- g/mL (grams per millilitre)
- g/cm³ (grams per cubic centimeter)
Conversion Relationships
1 kg/m³ = 1 g/L = 0.001 g/mL
Relative Density
Relative density compares the density of a substance with the density of water. It’s a number without units.
Formula: Relative Density = Density of substance ÷ Density of water
Example: If aluminum has density 2.7 g/cm³, its relative density is 2.7, meaning aluminum is 2.7 times denser than water.
Real-Life Application
Notice how some oil packets show “1 litre (910g)” – this tells us the oil is less dense than water (which would weigh 1000g for 1 litre).
Determination of density
To calculate density, we need to measure both mass and volume accurately using appropriate instruments and techniques.
How to measure mass?
Mass is the quantity of matter present in any object. We use balances to measure mass accurately.
Digital Weighing Balance Procedure
- Switch on the balance and ensure zero reading
- Place clean watch glass or butter paper on the pan
- Press tare/reset button to zero the reading
- Place the object carefully on the watch glass
- Record the mass reading displayed
Important Note
Most balances actually measure weight but display values in mass units. This works because weight and mass are closely related on Earth’s surface.
How to measure volume?
Volume is the space occupied by an object. Different methods are used for liquids and solids.
For Liquids – Measuring Cylinder
A measuring cylinder is a narrow, transparent cylindrical container with volume markings. Different sizes are available: 5mL, 10mL, 25mL, 50mL, 100mL, 250mL, etc.
Reading Accuracy
The accuracy depends on cylinder size:
| Cylinder Capacity | Smallest Reading |
|---|---|
| 10mL or 25mL | 0.1mL |
| 100mL | 1mL |
| 250mL | 2mL |
| 500mL | 5mL |
Proper Reading Technique
- Place cylinder on flat surface
- Pour liquid slowly to desired level
- Observe the curved surface (meniscus)
- Read at bottom of meniscus for colorless liquids
- Read at top of meniscus for colored liquids
- Keep eyes level with the reading
Why Tall and Narrow Design?
Measuring cylinders are designed tall and narrow rather than wide and short to improve measurement accuracy. The narrow shape makes small volume changes more visible.
Volume of Regular Solids
For objects with regular shapes like cubes or rectangular blocks:
Formula: Volume = Length × Width × Height
Example: A notebook with length 25cm, width 18cm, and height 2cm has volume = 25 × 18 × 2 = 900 cm³
Volume of Irregular Solids
For irregularly shaped objects like stones, we use the water displacement method:
Water Displacement Method
- Fill measuring cylinder with known volume of water
- Record initial water level
- Carefully lower the object into water
- Record final water level
- Volume of object = Final level – Initial level
Example Calculation
| Object | Initial Water Level | Final Water Level | Object Volume |
|---|---|---|---|
| Stone | 50mL | 55mL | 5mL = 5cm³ |
Calculating Density
Once we have both mass and volume measurements:
Example Calculation
- Mass of stone = 16.400g
- Volume of stone = 5cm³
- Density = 16.400g ÷ 5cm³ = 3.28 g/cm³
Earth’s Layered Structure
Our planet Earth shows how density affects large-scale structures. Earth has several layers with different densities:
Earth’s Layers (from outside to inside)
- Crust (lightest)
- Upper mantle
- Lower mantle
- Outer core (liquid)
- Inner core (solid, densest)
As we move toward Earth’s center, both pressure and temperature increase, making materials heavier and more compact.
Traditional Transportation
Ancient people understood density principles when choosing materials for water transport:
Bamboo Rafts
- Bamboo is light and hollow
- Low density makes it float easily
- Tied together to make rafts and boats
- Used for fishing, trading, and river crossing
Wooden Boats
- Strong trees provided good material
- Either hollowed out or used as rafts
- Locally available and naturally buoyant
- Still used in some regions today
Effect of temperature on density
Temperature changes affect density by influencing particle movement and spacing in matter.
General Temperature Effect
Heating Effect
- Particles move faster and spread out
- Volume increases while mass stays same
- Since Density = Mass/Volume, density decreases
- This explains why hot air rises (less dense than cold air)
Cooling Effect
- Particles move slower and come closer
- Volume decreases while mass stays same
- Density increases
Hot Air Balloons
Hot air balloons work on this principle – heated air inside is less dense than surrounding cool air, creating upward force.
Effect of pressure on density
Pressure affects different states of matter differently when it comes to density changes.
Effect on Gases
- Increasing pressure pushes gas particles closer together
- Volume decreases significantly
- Density increases substantially
Effect on Liquids
- Liquids are nearly incompressible
- Pressure has very small effect on volume
- Density change is minimal
Effect on Solids
- Solids are least affected by pressure
- Particles already very close together
- Density changes usually negligible
Special Case: Ice and Water
Ice floats on water because it’s less dense than liquid water. This happens because:
- Water has maximum density at 4°C
- When water freezes at 0°C, particle arrangement changes
- Ice structure takes up more space than liquid water
- Same mass in larger volume means lower density
- This property is crucial for aquatic life survival in winter
Ecological Importance
Ice floating on top of water bodies creates an insulating layer, keeping water underneath warm enough for fish and other aquatic life to survive in extremely cold weather.
Density Experiment Challenge
If you place a raw egg in tap water, it sinks because the egg is denser than water. Can you think of ways to make the egg float? This involves understanding how to change the density of either the egg or the water.
Our Scientific Heritage
Traditional salt production in India demonstrates practical application of solution principles.
Ningel Village Salt Production
Ningel village in Manipur’s Thoubal district continues ancient salt-making traditions:
Traditional Process
- Salt wells lined with 100-year-old tree trunks
- Families (mostly women) collect salty water
- Solution is boiled in large metal pans over firewood
- Water evaporates leaving salt crystals
- Crystals shaped into round ‘salt cakes’ using banana leaves
- Wrapped in traditional cloth (phanek) for protection
Cultural Significance
- More than just food production
- Represents history, culture, and beliefs
- Beautiful example of India’s living heritage
- Believed to have medicinal properties
- Sacred practice passed down through generations
This traditional method shows practical understanding of solution concentration, evaporation, and crystallization developed over centuries.
Summary Points
Understanding solutes, solvents, and solutions helps us comprehend many natural phenomena and industrial processes:
Basic Solution Concepts
- Solutions are uniform mixtures of solutes dissolved in solvents
- Solubility varies with temperature and pressure
- Saturated and unsaturated solutions have different properties
- Gas solubility behaves differently from solid solubility
Density and Its Applications
- Density determines floating and sinking behavior
- Temperature and pressure affect density differently
- Measurement techniques allow accurate density calculations
- Density explains many everyday observations
Practical Implications
- Solution principles apply in medicine, cooking, and industry
- Density concepts help in material selection and design
- Understanding these properties helps in problem-solving
- Traditional practices often demonstrate scientific principles
These concepts form the foundation for understanding more complex chemistry and physics topics in higher grades.
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