Lab: Percent Water in a Hydrate (Using Hot Plate) PDF

## Lab: Percent Water in a Hydrate (using Hot Plate) **Objective:** Calculate %H₂O in a hydrate compound **CuSO₄ · 5H₂O** *copper sulfate pentahydrate (II)* **Introduction:** Many substances (hydrates) have water (water of hydration) bound to them. For example, Sr(NO₃)₂ · 4H₂O, the hydrate, is com...

## Lab: Percent Water in a Hydrate (using Hot Plate) **Objective:** Calculate %H₂O in a hydrate compound **CuSO₄ · 5H₂O** *copper sulfate pentahydrate (II)* **Introduction:** Many substances (hydrates) have water (water of hydration) bound to them. For example, Sr(NO₃)₂ · 4H₂O, the hydrate, is composed of the salt Sr(NO₃)₂ which has four water molecules bound. In this lab, a hydrate of CuSO₄ · 5H₂O will be heated in a crucible until all the water is driven off. It should be noted that the initial blue sample will turn white as the water is driven off. The amount (in grams) of water can be determined by comparing the initial mass of your sample to the final mass after heating. The formula for percent composition will then be used to calculate the experimental percent water in the hydrate sample. **Materials:** * hot plate * electronic balance (+weigh paper, +weigh boat) * crucible (NO lid) * tongs * spatula * cooling pad **Procedure:** **Part A: Preparing the Crucible for Use (~25 minutes)** 1. Make sure the crucible does not have any cracks or chips. 2. Wash crucible (Note some "junk" is baked in and cannot be removed). Using crucible tongs, place a clean, dry porcelain crucible onto the balance. Measure the mass of the crucible and record the data. ***Do not handle the crucible with your hands, from this point forward, as the mass will be distorted due to oils on your hands.*** 3. Heat crucible on hotplate (set for ~10) and heat for ~5 minutes. Let cool ~5 minutes on wire gauze. 4. Measure the mass of the crucible again and record data. **Part B: Hydrate in Crucible** 1. Obtain a sample of hydrate on a weigh boat. 2. Using crucible tongs, place your clean, dry porcelain crucible on the balance. Measure the mass of the crucible and record the data. ***Remember: Do not handle the crucible with your hands, from this point forward, as the mass will be distorted due to oils on your hands.*** 3. Use a spatula to transfer about 2g of hydrate to the crucible. Measure the mass of the crucible with hydrate and record the data. 4. Place on hotplate, the sample in the crucible. Heat sample on hotplate for ~30 minutes. Note: You are looking for a "complete" change in color. 5. Place sample on cooling pad and cool for ~5 minutes. The crucible is cool enough when no heat is felt when your hand is held about 1 inch from the crucible. Measure the mass of crucible + sample. 6. Discard contents of crucible in waste container. 7. Wash and dry the crucible. Power down the hotplate in a safe manner. 8. Perform calculations. **Results:** **Part A** | Data | Value | |---|---| | Mass of crucible before heating | 14.62 g | | Mass of crucible after heating 1x | 14.61 g | **Part B** | Data | Value | |---|---| | Mass of hydrate | 2.0 g | | Mass of crucible & CuSO₄ before heating | 16.62 g | | Mass of crucible and salt after heating 1x | 14.23 g | | Mass of water lost | 0.39 g | | Percent water in hydrate | 19.5 | **Calculations:** **Conclusion:**