Question

ANAL0387: Percent Water in a Hydrate

3. The mass of a crucible and a hydrated salt was found to be 21.447 g. The mass of the crucible and the
anhydrous salt was 20.070 g. The mass of the crucible was 17.985 g.
(1) Calculate the mass of the hydrate heated.

Answer 1

To find the percent water in a hydrate, calculate the mass of the hydrate, the mass of the anhydrous salt, the water lost on heating, and divide the water mass by the hydrate mass, then multiply by 100% which is 39.77% H2O

Step-by-step explanation:

Calculating the Percent Water in a Hydrate:

To calculate the mass of the hydrate heated, we subtract the mass of the empty crucible from the mass of the crucible with the hydrate: 21.447 g (crucible + hydrate) - 17.985 g (empty crucible) = 3.462 g (hydrate). Then we find the mass of the anhydrous salt by subtracting the mass of the empty crucible from the mass of the crucible with the anhydrous salt: 20.070 g (crucible + anhydrous salt) - 17.985 g (empty crucible) = 2.085 g (anhydrous salt).

To calculate the mass of the water lost during heating, we subtract the mass of the anhydrous salt from the mass of the hydrate: 3.462 g (hydrate) - 2.085 g (anhydrous salt) = 1.377 g (H2O).

Lastly, to calculate the percent H2O, we divide the mass of the water by the mass of the hydrate and multiply by 100%:
(1.377 g H2O / 3.462 g hydrate) x 100% ≈ 39.77% H2O.

Answer 2

Mass of the hydrate heated = 3.462 g

Solution and Explanation:

• A hydrate is a salt or a compound that contains water of crystallization.
• For example, hydrated sodium carbonate which contains 10 moles of water of crystallization, Na₂CO₃ .10H₂O.
• In our case we are required to determine the mass of the hydrate;

Mass of the hydrate heated

Mass of the hydrate = mass of crucible and hydrate salt– mass of the crucible

Mass of crucible and hydrates salt = 21.447 g

Mass of the crucible = 17.985 g

Therefore;

Mass of the hydrate = 21.447 g – 17.985 g

= 3.462 g