Name
Lab Instructor
Date
Experiment 6—Determination of Formula of an Unknown Hydrate
Prelaboratory Exercises
1. Write the equation for the decomposition of the hydrate $Na_2SO_4 \cdot 10H_2O$. Label the
anhydrous salt.
2. A colorless crystalline compound when dissolved in water formed a colorless solution.
This compound was heated in a clean, dry test tube. This heating produced several drop-
lets of water on the upper region of the test tube. The residue was dissolved in water and
formed a yellow-brown solution.
a. Determine if this colorless crystalline compound is a true hydrate or not.
b. Give reasons.
3. A student heated an unknown hydrate, $Na_2SO_4 \cdot xH_2O$, in a crucible. The water was driven
off, leaving the anhydrous salt in the crucible. After cooling, the mass of the anhydrous
salt and water lost was calculated. The mass of the anhydrous salt was 0.695 g and the
mass of water lost was 0.895 g.
a. Calculate the moles of anhydrous salt in the sample. Show all steps. (The molar mass
of this salt is 142.04 g.)
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