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.
To prepare the solution, we will need following materials:
We will require the following apparatus to conduct the experiment:
Pestle and mortar
A beaker or bottle to collect filtered starch solution
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.
[Image will be Uploaded Soon]
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.
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?
a. Colloids are mixtures where one substance gets dispersed microscopically throughout another substance. Colloids come in many forms.
[Image will be Uploaded Soon]
2. What is Salvation?
a. 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?
a. 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?
a. 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.
a. Starch in water is a lyophilic solution.
6. Give an Example of a Lyophobic Solution.
a. 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.