Ceric ammonium sulfate (CAS), also known as cerium IV ammonium sulfate, is a chemical reagent used in redox titrations, particularly for the determination of ferrous ions. Here’s how to prepare and standardize both molar (1.0 M) and normal (1.0 N) solutions of ceric ammonium sulfate.
Preparation of 1.0 M Ceric Ammonium Sulfate Solution:
A 1.0 M ceric ammonium sulfate solution contains one mole of CAS in one liter of solution.
Materials Required:
– Ceric ammonium sulfate (CAS) crystals (molar mass varies, depending on the formula)
– Distilled water
– A balance
– A glass stirring rod
– A glass or plastic container
– A 1.0 L volumetric flask
Procedure:
1. Weigh out the required amount of ceric ammonium sulfate (CAS) to make a 1.0 M solution. The molar mass of CAS varies depending on the specific compound used; you’ll need to determine this based on the particular CAS formula you are working with.
2. Transfer the weighed CAS crystals into a clean and dry glass or plastic container.
3. Add distilled water to the container and stir the mixture with a glass stirring rod until the CAS crystals are completely dissolved. The final volume of the solution should be less than 1.0 L at this stage.
4. Transfer the solution into a 1.0 L volumetric flask. Rinse the container with distilled water to ensure all the CAS is transferred to the flask.
5. Fill the volumetric flask to the 1.0 L mark with distilled water while maintaining the temperature at a consistent level (usually 20°C). The solution is now a 1.0 M ceric ammonium sulfate solution.
Standardization of 1.0 M Ceric Ammonium Sulfate Solution to Prepare 1.0 N Solution:
To standardize the 1.0 M CAS solution and prepare a 1.0 N solution, you’ll need to determine its exact molar concentration.
Materials Required:
– A primary standard reagent, such as ferrous ammonium sulfate (FAS)
– Sulfuric acid (H2SO4)
– A burette
– A balance
– A 1.0 L volumetric flask
Procedure:
1. Weigh out a sample of a primary standard reagent, such as ferrous ammonium sulfate (FAS) of known purity. Accurately weigh about 0.0158 g of FAS. The molar mass of FAS is 392.14 g/mol.
2. Dissolve the weighed FAS in distilled water and transfer it into a 1.0 L volumetric flask.
3. Add a few drops of sulfuric acid (H2SO4) to the FAS solution. The sulfuric acid is added to acidify the solution and ensure that the FAS reacts completely with the CAS solution.
4. Prepare the burette with the 1.0 M CAS solution.
5. Titrate the FAS solution with the CAS solution until a color change occurs, indicating the completion of the reaction. The specific color change depends on the indicator used in the titration.
6. Record the volume of the CAS solution used for the titration. Use this volume to calculate the exact molar concentration of the CAS solution.
7. If the calculated molarity is close to 1.0 M, the solution can be considered a 1.0 N ceric ammonium sulfate solution. If not, adjust the concentration and re-standardize if necessary.
