A Level Chemistry Revision "Determining Water of Crystallisation by Titration"

Introduction

This tutorial guides you through the process of determining the water of crystallisation in a compound using titration. This practical experiment is common in A Level Chemistry and frequently appears in exams. You will learn how to accurately weigh a compound, prepare a solution, and perform a titration to find the water of crystallisation.

Step 1: Weighing the Compound

To begin, you need to accurately weigh the solid compound that contains water of crystallisation.

1. Gather your materials:

   • Analytical balance
   • Weighing boat or paper
   • The compound being tested

2. Follow these steps to weigh the compound:

   • Turn on the analytical balance and allow it to calibrate.
   • Place the weighing boat on the balance and tare it (zero it out).
   • Carefully add the solid compound to the boat until you reach the desired mass.
   • Record the mass of the compound for later calculations.

Step 2: Preparing the Solution

Next, you will prepare a solution with a known volume using a volumetric flask.

1. Collect the necessary equipment:

   • Volumetric flask (with a known capacity)
   • Distilled water
   • Funnel

2. Prepare the solution:

   • Transfer the weighed compound into the volumetric flask.
   • Add a small amount of distilled water to dissolve the compound.
   • Swirl the flask gently until the compound is fully dissolved.
   • Use the funnel to fill the flask with distilled water up to the calibration line.
   • Stopper the flask and invert it several times to mix the solution thoroughly.

Step 3: Setting Up the Titration

Now, you will set up the titration apparatus to measure the volume of titrant needed.

1. Gather your titration materials:

   • Burette
   • Titrant solution (e.g., sodium hydroxide or hydrochloric acid)
   • Pipette and pipette filler
   • Indicator solution (e.g., phenolphthalein or methyl orange)

2. Set up the titration:

   • Rinse the burette with the titrant solution, then fill it and clamp it vertically.
   • Use a pipette to transfer a measured volume of the prepared solution to a clean conical flask.
   • Add a few drops of the chosen indicator to the solution in the conical flask.

Step 4: Performing the Titration

You are now ready to perform the titration.

1. Carry out the titration:

   • Open the burette tap to allow the titrant to flow slowly into the conical flask.
   • Swirl the flask continuously to mix the solutions.
   • As you approach the endpoint (color change), add the titrant dropwise until a permanent color change occurs.
   • Record the final volume of titrant used.

2. Repeat the titration:

   • Perform at least three titrations for accuracy.
   • Calculate the average volume of titrant used.

Conclusion

In this tutorial, you have learned how to determine the water of crystallisation in a compound through careful weighing, solution preparation, and titration procedures. Now that you have collected your data, the next step is to perform calculations based on the titration results to determine the exact amount of water of crystallisation in your compound. This process not only enhances your practical skills but also aids in your understanding of solution chemistry.