HYDRATES
Purpose: Find the % water of Hydration and the Formula for an unknown hydrate.
Background Vocabulary
Hydrate Salt Anhydrous –
Procedure:
1. Record the formula of the unknown anhydrous salt.
2. Determine the mass of a clean dry crucible and lid. Record
3. Place approximately 1 g of the unknown hydrate into the crucible.
4. Determine the mass of the hydrate, crucible and lid. Record
5. With the lid slightly open, gently heat the crucible and contents for one minute. After this time, heat strongly for
five minutes.
6. Allow the crucible to cool to room temperature.
7. Determine the mass of the crucible and lid and contents. Record.
Data:
1. Formula of the unknown Hydrate __________·H2O
2. Mass of Empty Crucible and Lid _________g
3. Mass of crucible and lid and hydrate ______ g
4. Mass of crucible, lid and anhydrous ______g
Calculations:
% Water
1. Perform the subtractions needed to determine the mass of the unknown hydrate.
2. Perform the subtractions needed to determine the mass of the water of hydration.
3. Calculate percentage of water in the hydrate: %= [(grams of water) / (grams of hydrate)] x 100%
1. Mass of Hydrate
2. Mass of Water of Hydration
3. Percentage of water of hydration
Formula of Hydrate
1. Perform the subtraction needed to determine the mass of the anhydrous salt.
2. Convert the grams of anhydrous salt to moles
3. Convert the grams of water of hydration to moles.
4. Divide the moles of water by the moles of anhydrous salt to determine the formula of the hydrate. Report your
answer to the proper number of sig figs.
5. Write the formula for the hydrate.
1. Mass of Anhydrous Salt
2. Moles of Anhydrous Salt
3. Moles of water of Hydration
4. Ratio: Moles of Water PER Moles of Anhydrous Salt
5. Final Formula of Hydrate
Questions:
1. What could you do to make sure that in 5 minutes of heating all the water came out of the hydrate?
2. Define the terms hydrate and anhydrous.
3. A 1.500g sample of Na2S2O3·?H2O was heated until all of the water was removed. The mass of the residue after
heating was 0.956 g. Calculate the percentage of the water of hydration and the formula of the hydrate.