To find the mass of an unknown hydrate, you need to determine the mass of the hydrate itself by subtracting the mass of the empty dish from the mass of the dish and the hydrate before heating. Here's a detailed explanation:
Understanding Hydrates
Hydrates are chemical compounds that have water molecules incorporated into their crystal structure. When heated, these water molecules are released, leaving behind the anhydrous compound (the substance without water). To determine the mass of the hydrate, you measure before and after heating.
Step-by-Step Process to Find the Mass of a Hydrate
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Measure the mass of the empty dish:
- Start by weighing the empty dish or crucible that you'll use in the experiment. This is your initial measurement. Record it accurately.
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Measure the mass of the dish with the hydrate:
- Place the unknown hydrate sample into the empty dish.
- Weigh the dish with the hydrate together. Record this mass as mass of dish and hydrate before heating.
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Calculate the mass of the hydrate:
- Subtract the mass of the empty dish from the mass of the dish and hydrate before heating.
- Mass of the hydrate = Mass of the dish and hydrate before heating - mass of the empty dish.
For example, as provided by our reference: 7.4 g (dish and sample before heating) - 2.5 g (mass of empty dish) = 4.9 g, the mass of the hydrate.
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Heat the hydrate sample:
- Heat the dish containing the hydrate strongly for a specified duration, ensuring that all the water of hydration is driven off. Allow it to cool completely before proceeding.
- Important: Ensure that the heating removes all water molecules but does not decompose the compound.
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Measure the mass of the dish with the anhydrate:
- After cooling, weigh the dish and its content (the now anhydrous compound or anhydrate). This will be a lower mass than your previous measurement. Record this mass as mass of dish and sample after heating.
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Calculate the mass of the anhydrate:
- Subtract the mass of the empty dish from the mass of the dish and anhydrate after heating.
- Mass of the anhydrate = Mass of dish and sample after heating - Mass of the empty dish.
For example, as provided by our reference: 5.4 g (mass of dish and sample after heating) - 2.5 g (mass of empty dish) = 2.9 g, the mass of the anhydrate.
Summary in Table Format
| Measurement | Description | Example (g) |
|---|---|---|
| Mass of Empty Dish | Mass of the empty dish or crucible used in the experiment | 2.5 |
| Mass of Dish and Hydrate (Before Heating) | Mass of the dish containing the unknown hydrate before heating | 7.4 |
| Mass of Hydrate | Mass of the unknown hydrate = Mass of dish and sample before heating - mass of the empty dish | 4.9 |
| Mass of Dish and Anhydrate (After Heating) | Mass of the dish containing the anhydrous compound after heating | 5.4 |
| Mass of Anhydrate | Mass of the anhydrous compound = mass of dish and sample after heating - mass of the empty dish | 2.9 |
By following these steps, you can accurately determine the mass of an unknown hydrate and the mass of the resulting anhydrate after heating.
