Class IX- Chapter 5 - Exploring Mixtures and their Separation – II Classification of Mixtures: Solutions, Suspensions & Colloids

 Class  IX- Chapter 5 - Exploring Mixtures and their Separation – II

Classification of Mixtures: Solutions, Suspensions & Colloids

Mixtures can be classified based on the size of particles and their properties into:

· Solutions

· Suspensions

· Colloids

1. Solution

Definition: A solution is a homogeneous mixture in which one substance (solute) is completely dissolved in another (solvent).

Properties:· Homogeneous (uniform)

· Particle size is very small (< 1 nm)

· Particles not visible

· Do not scatter light (no Tyndall effect)

· Cannot be separated by filtration

· Stable (do not settle down)

· Examples: Salt in water, Sugar in water, Copper sulphate solution

      Terms related to Solution

1. Dilute and concentrated solutions –

A solution having a small amount of solute in a given solvent is dilute, whereas a large amount of solute in that same given solvent is concentrated when compared with one another.

2. Unsaturated and saturated solution -

- A solution that can dissolve more solute in it at a given temperature is called an unsaturated solution.

- A solution which contains the maximum amount of solute dissolved in a given quantity of solvent at the given temperature and which cannot dissolve any more solute at that temperature is called a saturated solution.

3. Solubility – The maximum amount of solute that can be dissolved in a given amount of solvent is called the solubility of that solute in that solvent at a particular temperature.

4. Effect of Temperature on Solubility –

(a) Solubility of Solid Solute in Liquids 

• - As temperature increases, solubility also increases.
  
  - Saturated solution becomes unsaturated.
  
  - If a saturated solution is cooled down, some dissolved solute separates.
  
  (b) Solubility of Gas in Liquid:
  
  - As temperature increases, solubility decreases.
  
  5. Concentration of Solution –
  
  The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution.
  
  Concentration of Solution = Amount of solute / Amount of solution
  
  The concentration of a solution can be calculated in terms of m/

m,           m/v, or v/v.

2. Suspension

Definition: A suspension is a heterogeneous mixture in which particles are large and settle down when left undisturbed.

Properties:

• ·        Heterogeneous
• ·        Particle size large (> 1000 nm)
• ·        Particles are visible
• ·        Scatter light
• ·        Can be separated by filtration
• ·        Unstable (particles settle down)

·        Examples: Sand in water, Chalk powder in water, Muddy water

1. 3. Colloid
   
   Definition: Solutions in which the size of particles lies between those of true solutions and suspensions are called colloidal solutions or simply colloids. There are two phases in a colloidal solution. These are known as the dispersed phase and dispersion medium.
   
   The component present in a smaller proportion is the dispersed phase, while the one present in a greater proportion is the dispersion medium.

         Properties:

• ·        Appears homogeneous but actually heterogeneous
• ·        Particle size intermediate (1–1000 nm)
• ·        Particles not visible to the naked eye
• ·        Show Tyndall effect (scatter light)
• ·        Cannot be separated by filtration
• ·        Stable (do not settle)

·        Examples: Milk, Fog, Smoke, Butter

·        Types of colloids –

Dispersed Phase	Dispersion Medium	Type	Examples
1. Solid	Solid	Solid Sol	Milky glass
2. Solid	Liquid	Sol	Muddy water
3. Solid	Gas	Solid aerosol.	Smoke
4. Liquid	Solid	Gel	Jelly
5. Liquid	Liquid	Emulsion	Milk
6. Liquid	Gas	Aerosol	Fog
7. Gas	Solid	Solid foam	Pumice stone
8. Gas	Liquid	Foam	Shaving cream

 4. Difference Between Solution, Suspension & Colloid

Property	Solution	Colloid	Suspension
Nature	Homogeneous	Heterogeneous (appears homogeneous)	Heterogeneous
Particle Size	< 1 nm	1–1000 nm	> 1000 nm
Visibility	Not visible	Not visible	Visible
Tyndall Effect	No	Yes	Yes
Stability	Stable	Stable	Unstable
Filtration	Not possible	Not possible	Possible

             5.

Activity

Take 3 glasses:

1. Salt + water → Solution

2. Milk + water → Colloid

3. Sand + water → Suspension

Observation: Which settles? → Suspension, which scatters light? → Colloid

6. Key Concept

· Smallest particles → Solution

· Medium particles → Colloid

· Largest particles → Suspension

7. Practice Questions

1. Define a solution with an example.

2. Why do suspensions settle down?

3. What is the Tyndall effect? Which mixture shows it?

4. Classify the following:

o Milk → __________

o Salt water → __________

o Muddy water → __________