Colloids Class 12 Terminal Questions with Answer NIOS
National Institute of Open Schooling (NIOS)
Sr. Secondary, Module-3
Lession-8: Colloids Terminal Questions with Answer
Terminal QUESTIONS with Answer
1. List three differences between a true solutions and a colloidal solutions.
Answer:| True Solution | Colloidal Solution |
|---|---|
| It is a homogenous solution | It is a heterogenous solution |
| The size of the particles is less than 1nm | The size of the particles is 1-1000nm |
| does not show Tyndall effect and Brownian movement | show Tyndall effect and Brownian movement |
2. Describe one method of preparation of
a. Lyophilic colloid
b. Lyophobic colloid
Answer:
Lyophilic colloids (water loving): The colloidal solutions in which the particles of the dispersed phase have a great affinity for the dispersion medium, are called lyophilic collodis. Lyophilic colloids can be prepared just by heating the solid with the medium in which it is dispersed. For example, the substance like gelatin, gum, starch, egg, albumin etc. pass readily into water to give colloidal
solution.
Lyophobic colloids (water hateing): The colloidal solutions in which there is no affinity between particles of the dispersed phase and the dispersion medium are called lyophobic colloids. Lyophobic sols have many methods for preparation as it is not simple to form. There are mainly two methods for its preparation- One is Condensation methods and other is Dispersion methods.
1. Bredig's Arc Method
An electric arc is struck between the two metallic electrodes placed in a container of water. The intense heat of the arc converts the metal into vapours, which are condensed immediately in the cold water bath. This results in the formation of particles of colloidal size. We call it as metal sol. e.g. gold sol.
3. What are associated colloids?
Answer:
Associated colloids are the colloids which act as electrolyte at low concentration and show colloidal behaviour at high concentration due to the formation of aggregated particles. The aggregates particles are called micelles. Soaps and detergents are the examples of associated colloids.
4. What is Brownian motion? How does it originate?
Answer:
Robert Brown, a botanist discovered in 1827 that the pollen grains suspended in water do not remain at rest but move about continuously and randomly in all directions. Later on, it was observed that the colloidal particles are moving at random in a zig – zag motion. This type of motion is called Brownian movement. The molecules of the dispersion medium are constantly colloiding with the particles of the dispersed phase. It was
stated by Wiener in 1863 that the impacts of the dispersion medium particles are unequal, thus causing a zig-zag motion of the dispersed phase particles. The Brownian movement explains the force of gravity acting on colloidal particles. This helps in providing stability to colloidal sols by not allowing them to settle down.
5. Why bleeding from a fresh cut stops on applying alum?
Answer:
Blood is a colloidal solution of an albuminoid substance. So, it contains charged protein molecules. Moist alum has highly charged
Al+3 and SO42− ions which neutralize the charged protein molecules present in blood. This results in coagulation of blood, forming a clot which stops further bleeding.
6. Two beakers A and B contain ferric hydroxide sol and NaCl solution respectively. When a beam of light is allowed to converge on them, (in a darkened room), beam of light is visible in beaker A but not in breaker B. Give the reason. What is this effect called?
Answer:
when light passes through beaker A (colloidal solution), the light can pass through it, i.e, Tyndall effect is occured. if it passes through beaker B (true solution), the light can't pass through it, i.e, Tyndall effect is not occured. Tyndall effect means the passing of a beam of light through a medium.
7. Define the following terms and give two examples of each
i. Gel
ii. Sol
Answer:
A sol is a colloidal solution in which dispersed phase is a solid and dispersion medium is a liquid. Examples are Au, As2S3, S in water, paints, milk of magnesia.
A gel is a colloidal solution in which dispersed phase is a liquid and dispersion medium is a solid. examples are cheese, butter, jellies.
8. Describe two important applications of colloidal solutions.
Answer:
Applications of Colloidal solutions are-
1. A colloid is used as thickening agents in industrial products such as lubricants, lotions, toothpaste, coatings, etc.
2. In the manufacture of paints and inks, colloids are useful. In ball-point pens, the ink used is a gel (liquid-solid colloid).
9. Give two examples of emulsions used in daily life.
Answer:
Milk and cold cream are examples of emulsion in our daily life.
10. Explain the role of emulsifier in an emulsion?
Answer:
The most important role of an emulsifier is to stabilize an emulsion as it prevents the substance of same medium to bond And creates a stronger bond between the particles of different medium.
11. What are nano materials? Give their three applications.
Answer:
Materials having dimensions in nanoscale range are called nanomaterials. Applications- Batteries and supercapacitors, magnetic material and drug delivery.
