THE HETEROGENEOUS MIXTURES – SUSPENSIONS AND COLLOIDS WORKING MODEL

THE HETEROGENEOUS MIXTURES – SUSPENSIONS AND COLLOIDS

Heterogeneous mixtures are composed of two or more substances that are physically combined but not chemically bonded. Among heterogeneous mixtures, suspensions and colloids are two distinct types, each with unique characteristics and properties. Let’s delve into each:

**1. Suspensions:**
– Suspensions are heterogeneous mixtures in which solid particles are dispersed in a liquid or gas medium.
– The particles in suspensions are typically larger than those found in solutions and colloids and can be seen with the naked eye.
– However, these particles are not dissolved but rather suspended throughout the medium and tend to settle out over time due to gravity.
– Suspensions can be separated by filtration, where a porous material (such as filter paper) is used to separate the solid particles from the liquid or gas medium.
– Examples of suspensions include muddy water (suspended soil particles in water), sand in water, and flour in water.

**2. Colloids:**
– Colloids are heterogeneous mixtures in which tiny particles (between 1 and 1000 nanometers in size) are dispersed evenly throughout a continuous medium, such as a liquid, gas, or solid.
– Unlike suspensions, the particles in colloids are not easily visible under a microscope, but they do scatter light, causing the mixture to appear cloudy or opaque.
– Colloids exhibit the Tyndall effect, where they scatter light when a beam of light is passed through them, making the light beam visible.
– Colloids do not settle out over time, as the dispersed particles are small enough to remain suspended indefinitely due to Brownian motion.
– Common examples of colloids include milk (emulsion of fat globules in water), fog (suspension of water droplets in air), whipped cream (foam of air bubbles in liquid fat), and gelatin (colloid of protein molecules in water).

**Distinguishing Characteristics:**
1. **Particle Size:** Suspensions have larger particles that can be seen with the naked eye, while colloids have smaller particles that are not visible but can scatter light.

2. **Settling:** Suspensions settle out over time due to gravity, while colloids remain suspended indefinitely due to Brownian motion.

3. **Clarity:** Suspensions appear cloudy or opaque, while colloids may appear clear or translucent until a light source is passed through them, revealing the Tyndall effect.

In summary, suspensions and colloids are both heterogeneous mixtures, but they differ in particle size, settling behavior, and appearance. Understanding these distinctions is crucial for various applications in science, industry, and everyday life.

Suspensions:

1. Definition:
   • A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid or gas medium.
   • The particles in a suspension are large enough to settle out over time due to gravity, resulting in the formation of sediment at the bottom of the container.
2. Particle Size:
   • Suspended particles are typically larger than 1 micrometer (µm) in diameter.
   • They are visible under a microscope and can be seen with the naked eye.
3. Examples:
   • Muddy water: Soil particles suspended in water.
   • Orange juice with pulp: Solid pulp particles suspended in liquid juice.
   • Paint: Pigment particles suspended in a liquid medium.
4. Settling:
   • Suspended particles settle out over time due to gravity.
   • To maintain a suspension, the mixture must be continuously stirred or agitated.

Colloids:

1. Definition:
   • A colloid is a heterogeneous mixture in which one substance (the dispersed phase) is dispersed evenly throughout another substance (the continuous phase).
   • The particles in a colloid are intermediate in size between those in a solution and those in a suspension.
2. Particle Size:
   • Colloidal particles range in size from 1 nanometer (nm) to 1 micrometer (µm) in diameter.
   • They are not visible under an ordinary microscope but can scatter light, causing the mixture to appear cloudy.
3. Examples:
   • Milk: Fat globules dispersed in a water-based solution.
   • Fog: Liquid water droplets suspended in air.
   • Gelatin: Protein molecules dispersed in water.
4. Stability:
   • Colloidal particles remain dispersed throughout the medium and do not settle out over time.
   • The stability of a colloid depends on factors such as particle size, charge, and interactions with the medium.

Key Differences:

1. Particle Size:
   • Suspended particles are larger and visible to the naked eye, while colloidal particles are smaller and not visible under an ordinary microscope.
2. Settling:
   • Suspended particles settle out over time, whereas colloidal particles remain dispersed throughout the medium.
3. Appearance:
   • Suspensions may appear cloudy or opaque due to the presence of visible particles, while colloids may appear translucent or slightly cloudy due to the scattering of light by the dispersed particles.

Understanding the differences between suspensions and colloids is important in various fields such as chemistry, biology, and environmental science, as it helps in characterizing and analyzing different types of mixtures and their properties.