Question

A student was determining the formula for the hydrate of barium chloride, $Ba{Cl}_2$ in a laboratory. The student cleaned, dried, and determined the mass of the crucible and cover and then added a sample of the hydrate to the crucible and determined the mas after that the sample was heated in crucible strongly for 10 minutes. The sample in the crucible and cover was cooled and the mass was determined. The mass data is provided in the table below:

Mass of crucible and cover	31.623 grams
Mass of crucible, cover, and sample prior to heating	33.632 grams
Mass of crucible, cover, and sample after heating	33.376 grams

After heating, determine how many moles of water were removed from the sample?

• A. 0.0142 moles
• B. 0.0974 moles
• C. 0.112 moles
• D. 0.256 moles
• E. 1.85 moles

Answer 1

Answer: (A)

0.0142 moles

Mass of crucible, cover, and sample prior to heating = 33.632 grams
Mass of crucible, cover, and sample after heating = 33.376 grams
Mass of water removed $=33.632-33.376=0.256$ grams
The molar mass of water is 18 g/mol.
The mass of water removed $=\frac{0.256}{18}=0.0142$ moles.