Chemistry
Chemistry
Problem
Each of the following hydrate samples has a mass of 15.0 g. All samples are pure. • Copper(II) sulfate pentahydrate, CuSO₄·5H₂O • Barium chloride dihydrate, BaCl₂·2H₂O • Sodium carbonate decahydrate, Na₂CO₃·10H₂O • Calcium sulfate hemihydrate, CaSO₄·½H₂O (molar ratio 0.5 mol H₂O per mol CaSO₄) (a) Determine the molar mass of each hydrate sample listed. (b) Calculate the number of moles of formula units present in each 15.0 g sample. (c) Rank the four samples from the greatest to the fewest number of formula units present. Show relevant reasoning. (d) If all waters of hydration were released upon heating, rank the samples from the greatest to the fewest number of water molecules that would be produced. Include supporting calculations or logic.Intuitive explanation
Hydrates contain water molecules locked into their crystal structure, so their molar mass is larger than the anhydrous salt alone. To compare these samples fairly—even though they all weigh 15.0 g—you need to calculate each compound's molar mass (including the water), then use that to find moles and ultimately the number of water molecules or moles of water in each sample. The key is recognizing that the same mass of different hydrates contains different amounts of the water component.
Intuitive explanation
Hydrates contain water molecules locked into their crystal structure, so their molar mass is larger than the anhydrous salt alone. To compare these samples fairly—even though they all weigh 15.0 g—you need to calculate each compound's molar mass (including the water), then use that to find moles and ultimately the number of water molecules or moles of water in each sample. The key is recognizing that the same mass of different hydrates contains different amounts of the water component.