Question

How many of these solutions are colloid here? Butter, Smoke, Pumic stone, milk, sugar solution, Aq solution of \(\mathrm{C}_{2} \mathrm{H}_{5}\) OH Ruby glass, cold cream, Paints.

Short answer

There are 6 colloids: Butter, Smoke, Milk, Ruby Glass, Cold Cream, and Paints.

Step-by-step solution

Definition of Colloid

A colloid is a mixture where one substance is dispersed evenly throughout another, and the particles do not settle out easily. These particles are typically between 1 nanometer and 1000 nanometers in size. Examples of colloids include gels, emulsions, and foams.

Classifying Each Substance

1. **Butter** - This is a colloidal substance, an emulsion of water in fat.2. **Smoke** - Considered a colloid because it consists of solid particles dispersed in air.3. **Pumice Stone** - Not a colloid; it is a solid substance with air pockets.4. **Milk** - A colloid; it is an emulsion of fat in water.5. **Sugar Solution** - Not a colloid; it is a true solution.6. **Aqueous solution of \( ext{C}_{2} ext{H}_{5} ext{OH}\)** - A true solution of alcohol in water, not a colloid.7. **Ruby Glass** - Considered a colloid as it is glass with gold particles dispersed.8. **Cold Cream** - A colloid, typically an emulsion.9. **Paints** - A colloid, as it contains pigment particles dispersed in a medium.

Counting the Colloid Examples

After classifying each item, count the number of colloids identified: Butter, Smoke, Milk, Ruby Glass, Cold Cream, and Paints. This results in a total of 6 colloids.

Key concepts

Colloidal Solutions

Colloidal solutions are fascinating mixtures where tiny particles are evenly distributed throughout another substance. These particles, known as the dispersed phase, do not settle out easily and usually range in size between 1 nanometer and 1000 nanometers. This characteristic size range is what makes colloidal solutions unique compared to other types of mixtures.
In colloids, the dispersing medium can be in the form of a gas, liquid, or solid, paired with an appropriate dispersed phase. Common examples of colloidal solutions include aerosols like smoke, emulsions like milk and mayonnaise, or foams like whipped cream.
One of the main features that distinguish colloids from other mixtures is their stability. Due to the small size of the particles, they can stay suspended for long periods without settling, which is not the case in suspensions. Colloidal solutions also scatter light due to the Tyndall effect, making a light beam visible as it passes through. This is another tell-tale sign that you are dealing with a colloidal solution.

Emulsions

Emulsions are a special type of colloidal solution where the dispersed phase and the dispersing medium are both liquids. They form when two liquids that usually don't mix, like oil and water, are made to mix with the help of an emulsifying agent. The emulsifying agent stabilizes the mixture, preventing the liquids from separating.
Milk and mayonnaise are classic examples of emulsions. In milk, fat droplets are dispersed in water, while mayonnaise consists of oil dispersed in vinegar or lemon juice.
There are two basic types of emulsions:

• **Oil-in-water (O/W)**: Oil droplets are dispersed in a continuous water phase, as seen in milk.
• **Water-in-oil (W/O)**: Water droplets are dispersed in a continuous oil phase, such as in butter.

Emulsions can be used in various industries, from culinary arts to cosmetics, showcasing their versatility in daily life.

Dispersed Particles

Dispersed particles in colloidal solutions are the small units that stay evenly distributed throughout the dispersing medium. The size of these particles typically falls between 1 and 1000 nanometers, which is crucial for maintaining the stability of colloids.
Dispersed particles can be solid, liquid, or gas, depending on the type of colloid. For example, smoke consists of solid dispersed particles in a gas, while in whipped cream, gas bubbles are dispersed in a liquid.
The nature of dispersed particles greatly impacts the properties of the colloid. Their interaction with the dispersing medium, along with other forces like electrostatic and van der Waals forces, determine the stability and behavior of the colloid.
Advanced techniques such as ultramicroscopy and dynamic light scattering are often used to study and understand the behavior of dispersed particles in colloidal solutions.

True Solutions

True solutions are homogeneous mixtures where the solute is completely dissolved in the solvent. The particle size in true solutions is typically less than 1 nanometer, which is much smaller than the particles found in colloidal solutions.
These solutions are characterized by their inability to scatter light, which means they appear clear and transparent. This lack of light scattering is due to the very small size of the solute particles, which are usually molecules or ions.
Common examples of true solutions include sugar dissolving in water and alcohol dissolving in water, as seen in the aqueous solution of \\( \mathrm{C}_{2} \mathrm{H}_{5}\mathrm{OH} \).
True solutions exhibit the principle of diffusion, where the solute moves freely throughout the solvent, resulting in a uniform composition. This makes true solutions different and unique compared to colloidal solutions.