Introduction to Prepare Colloidal Solution of Starch
Starch is a tasteless and odourless white powder which is a carbohydrate and is a major component of human diet. Starch is found in abundance in all day to day edible substances such as rice, corn and potato. Starch comprises amylose and amylopectin, and their relative percentages vary depending on the source of starch.
Starch forms a lyophilic solution with water when heated. The OH group present in starch molecules can form hydrogen bonding with water molecules. Because of this, there is attraction between starch and water molecules which make it a stable lyophilic solution. Starch particles are highly solvated in water.
Experiment to Prepare Colloidal Solution of Starch
As explained above, starch forms a lyophilic colloidal solution with water when heated at a certain temperature. In this section, we will describe the process of doing the same in a chemistry lab.
Material Required
To prepare the solution, we will need following materials:
Soluble starch
Distilled water
Filter paper
Apparatus Required
We will require the following apparatus to conduct the experiment:
250ml beaker
50ml beaker
Funnel
Glass rod
Pestle and mortar
Wire gauze
Bunsen burner
Tripod stand
Electronic balance
A beaker or bottle to collect filtered starch solution
Procedure
First of all, we need to determine how much solution we want to prepare. Let’s say you want to prepare the solution in 100ml of water. For that, we will need a small quantity of starch. Hence, you will need to use the electronic weighing machine or electronic balance to to weigh 0.5g to 1g of soluble starch.
After weighing starch, take the weighed quantity and transfer it into a mortar. Also add a few ml of distilled water. Now, use the pestle to grind the starch into a thin paste. Transfer the paste into a 50ml beaker.
Now, take about 100ml of distilled water in the larger (250ml) beaker. Put the wire gauze on the tripod stand and the Bunsen burner underneath it. Start the burner and place the 250ml beaker (with 100ml water) on the wire gauze. Heat the beaker till water starts boiling.
When water starts boiling, start pouring the starch paste which we have in a smaller (50ml) beaker. Stir continuously with the glass rod while doing so. Boil the water and starch mixture for about 10 mins. Post that, place the beaker aside to let it cool.
When the beaker cools down, we need to filter the solution. To do this, take a funnel and place a filter paper inside it. Pour the starch solution through the filter paper and funnel and collect it in another vessel.
The filtrate thus collected is the lyophilic starch solution.
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Figure 1: Preparation of Starch Solution
Precaution to be taken while preparing starch solution
As you saw in the previous section, it is not a very complex experiment. But still, you need to take care of a few things in order to make sure the experiment is successful.
First and foremost, please ensure that the apparatus (beakers, mortar and other things) that you intend to use for this experiment are properly cleaned. Any dirt or impurities may render the experiment unsuccessful.
Both the materials, i.e. starch and water should be of good quality. Make sure the starch powder is clean and white in colour. Always use distilled water for the experiment. When you make the starch paste in mortar, make sure it doesn’t have any granules and is a fine paste.
Do not add the starch paste to cold water. Wait for water to start boiling. And when you add the paste to boiling water, add it slowly forming a thin stream. Stir continuously to avoid any precipitates to be formed. Keep on stirring till the contents are fully dissolved in water.
Viva Voice
An additional component of viva voice can be the questions which the examiner can ask during the practical exam. Here, we are giving a list of some questions which can be asked during viva voice, especially on this topic.
1. What are Colloids?
Colloids are mixtures where one substance gets dispersed microscopically throughout another substance. Colloids come in many forms.
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2. What is Salvation?
Solvation is the process by which solute and solvent molecules interact with each other. During salvation, the solute and solvent molecules are reorganized into solvent complexes where solute ions are surrounded by a concentric shell of solvent ions.
3. What is Starch?
Starch is a type of carbohydrate which is one of the main components of human diet. Pure starch is a tasteless and odourless white powder.
4. What are Lyophilic and Lyophobic Colloid Solutions?
Lyophilic solutions are solvent attracting solutions where solute particles are solvated by the solvent particles. Lyophobic solutions are solvent repelling solutions where the solution is stabilized by the charge on colloidal particles, rather than their salvation.
5. Give an Example of a Lyophilic Solution.
Starch in water is a lyophilic solution.
6. Give an Example of a Lyophobic Solution.
Ferric hydroxide in water is a lyophobic solution.
This ends our coverage on the topic “To prepare colloidal solution of starch”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to perform the experiment easily and understand the chemistry behind it. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.
FAQs on To Prepare Colloidal Solution of Starch
1. What is the step-by-step procedure to prepare a colloidal solution of starch in a lab?
To prepare a colloidal solution (or sol) of starch, follow these steps as per the CBSE curriculum for the 2025-26 session:
- First, create a thin paste by mixing about 1 gram of soluble starch with a small amount of cold water in a beaker.
- Next, heat approximately 100 mL of distilled water in a separate, larger beaker until it reaches a rolling boil.
- Slowly pour the starch paste into the boiling water while stirring continuously with a glass rod to prevent lumps.
- Continue to heat the mixture for about 2-3 minutes until a translucent solution is formed.
- Finally, allow the beaker to cool down. The resulting translucent mixture is the colloidal sol of starch.
2. What kind of colloid is a starch solution?
A starch solution in water is a classic example of a lyophilic colloid. The term 'lyophilic' means 'liquid-loving', indicating that the dispersed phase (starch particles) has a strong affinity for the dispersion medium (water). It is also classified as a macromolecular colloid, where large polymers like starch molecules are dispersed in a solvent.
3. What is the standard test to confirm the formation of a starch sol?
The presence of starch in the prepared solution is confirmed using the iodine test. To perform this test, take a small amount of the cooled starch sol in a test tube and add a few drops of dilute iodine solution. The appearance of a distinct deep blue or violet colour confirms the presence of starch and the successful formation of the sol.
4. What specific materials and apparatus are required for this experiment?
To prepare a starch colloidal solution in a school laboratory, you will typically need the following:
- Apparatus: A 250 mL beaker, a 100 mL beaker, a glass rod for stirring, a tripod stand, wire gauze, and a Bunsen burner.
- Chemicals: Soluble starch powder and distilled water.
5. Why is it necessary to add the starch paste to boiling water and not the other way around?
This procedure is critical for forming a stable colloid. Starch granules are not very soluble in cold water. By adding the paste to boiling water, the high temperature causes the starch granules to rupture and disperse evenly, forming particles of the correct colloidal size (1-1000 nm). If hot water were added to the cold paste, it would likely create lumps and an uneven mixture, failing to form a proper sol.
6. How does a colloidal solution of starch differ from a true solution and a suspension?
A starch sol has properties intermediate between a true solution (e.g., salt in water) and a suspension (e.g., sand in water):
- Particle Size: Starch particles are larger than ions in a true solution but smaller than particles in a suspension.
- Appearance: A starch sol is translucent (cloudy but allows light to pass), while a true solution is transparent and a suspension is opaque.
- Stability: A starch sol is stable and its particles do not settle over time due to gravity, unlike a suspension.
- Filtration: Colloidal particles pass through ordinary filter paper but can be separated using a semi-permeable membrane.
7. What is the Tyndall effect, and can it be observed in a freshly prepared starch sol?
The Tyndall effect is a key property of colloids where the particles are large enough to scatter a beam of light, making its path visible. Yes, this effect can be clearly observed in a prepared starch sol. If you pass a beam of light (from a laser or torch) through the beaker in a darkened room, the path of light will become illuminated and visible as it passes through the sol. This does not happen in a true solution.
8. Why is a starch sol considered a highly stable colloid?
A starch sol is a lyophilic colloid, which contributes to its high stability. The starch particles (dispersed phase) are extensively hydrated, meaning they are surrounded by a protective layer of water molecules (dispersion medium). This hydration layer prevents the starch particles from coming into contact and clumping together (coagulating), thus ensuring the stability of the sol.
9. What could be the reason if the prepared starch solution appears very cloudy or settles down?
If a prepared starch solution is excessively cloudy or its particles settle, it indicates that a proper colloid was not formed. The most common reasons include:
- Incorrect Temperature: The water was not at a full boil when the starch paste was added.
- Improper Mixing: The starch paste was added too quickly or without continuous stirring, causing lumps to form instead of colloidal particles.
- High Concentration: Too much starch was used relative to the amount of water, creating a mixture closer to a suspension.
