Titration is a common chemistry laboratory method for quantitative analysis of the concentration of a substance.
The simple gist of it is that you have a solution of known volume and concentration (Titrant) and you periodically drop the solution into the unknown substance (Analyte) which has an indicator and a color change will happen.
Then when the analyte changes color you note down how much titrant you used and from there you can find the concentration of the analyte.
This is commonly used in the food industry and the dietary supplement industry, where it can be used to test the amount of salt or a specific mineral/vitamin is in a sample.
In this article, I will show you how to perform a simple titration, which can be used for many different purposes.
I will be showing a titration using a Vitamin C supplement pill, and check for the concentration of vitamin C in it.
The pill dissolved in water will be my analyte, my indicator will be soluble starch, and my titrant will be an iodine solution.
Background Info (Theory):
The whole idea behind titration is that you have an indicator that changes the color of the solution.
For vitamin, C starch is added and when it interacts with free-flowing iodide ions it changes color to a reddish.
So when the iodine solution is added to the vitamin C (ascorbic acid) it changes to dehydroascorbic acid and the iodine added turns into iodide ions, which then interact with the starch.
When the color is permanent that is called the endpoint, which is where you stop, and then by using simple stoichiometry you can find the concentration and mass of vitamin C in the sample.
Step 1 (Iodine Solution):
First, you need to weigh out 2 g potassium iodide on a scale and transfer it into a 100 mL beaker.
Then weigh out 1 g iodine and add to the same beaker and add 2-3 mL water and swirl until all of the iodine is dissolved.
Then transfer the solution to a 1 L volumetric flask and fill it up to the 1 L mark with water, this will give you a 0.005M concentration.
Step 2 (Starch Indicator):
First, weigh out 0.25 g of soluble starch, the bring 50 mL of water to a boil in a pot.
Add the soluble starch to the pot and mix and let it cool off.
Add the Vitamin C tablet to 200 mL of water and stir until it is completely dissolved.
Then transfer the vitamin C solution into a volumetric flask using a pipette until it is up to 100 mL.
Then take 20 mL of your Vitamin C solution and put it into a 250 mL flask and add 150 mL of water, and 1 mL of starch solution.
Step 3 (Titration and Calcuation):
Add the iodine solution to a burette or if you don’t have one you can use a big pipette, but just know the starting volume of it and remember to count the drops.
Then slowly let a few drops of the iodine solution get into the mixture and then swirl the flask.
Do this over and over again, until the solution changes color to red permanently.
Then you can use the below calculations to find the moles and therefore molarity/concentration or mass of vitamin C in your solution, for me, it was 0.088M.