Calculate the moles of water removed and the moles of anhydrous calcium sulfate remaining in the crucible.

Question

In a crucible, a 1.803g sample of hydrated calcium sulfate (CaSO4 . XH2O) is heated until a constant mass is reached. The mass of the anhydrous calcium sulfate is 1.426g.

Answer 1

1.803 g - 1.426 g = 0.377 g H₂O /18 = 0.0209 mols

mols anhydrous CaSO4= 1.426 g / 136 g/mol = 0.0105 mol

Divide both by 0.0105 to get whole numbers

0.0209/0.0105 = 2 moles H2O

0.0105/0.0105 = 1 mole CaSO4

Formula = CaSO4-2H2O

calcium sulfate dihydrate

Answer 2

To calculate the moles of water removed and the moles of anhydrous calcium sulfate remaining, we first need to determine the number of moles of hydrated calcium sulfate present in the original sample.

Calculate the molar mass of hydrated calcium sulfate:

Molar mass of CaSO4 = 40.08 g/mol (1 calcium atom + 1 sulfur atom + 4 oxygen atoms)

Molar mass of H2O = 18.02 g/mol (2 hydrogen atoms + 1 oxygen atom)

Molar mass of CaSO4 . xH2O = 40.08 g/mol + x(18.02 g/mol) = 40.08 g/mol + 18.02x g/mol = (40.08 + 18.02x) g/mol

Calculate the number of moles of hydrated calcium sulfate in the original sample:

n = m/M

where n = number of moles, m = mass, and M = molar mass

n = 1.803 g / (40.08 + 18.02x) g/mol

Calculate the number of moles of anhydrous calcium sulfate formed:

n(anhydrous) = m(anhydrous) / M(anhydrous)

where m(anhydrous) = 1.426 g and M(anhydrous) = 136.14 g/mol (molar mass of CaSO4)

n(anhydrous) = 1.426 g / 136.14 g/mol = 0.01047 mol

Calculate the moles of water removed:

The difference between the number of moles of hydrated calcium sulfate and the number of moles of anhydrous calcium sulfate is equal to the number of moles of water removed:

n(water) = n(hydrated) - n(anhydrous)

n(water) = [1.803 g / (40.08 + 18.02x) g/mol] - 0.01047 mol

Note: We cannot determine the exact value of x (the number of water molecules in the hydrated compound) from the given information. However, we can still calculate the moles of water removed and the moles of anhydrous calcium sulfate remaining using the formula above.