when 1.87 g of gypsum(hydrated calcium sulfate) was heated to constant mass, it lost 0.39 g of water. What is the formula of gypsum?
YOu know it is of the form: CaSO4.XH2O
the idea here is to find x.
calculate the number of moles of water in .39g.
Calculate the number of moles of CaSO4 in 1.87-.39 g.
divide the moles of water by the moles of CaSO4. That is x
Now, the lesson: Why is this so?
The formula of gypsum is CaSO4.xH2O, where x represents the number of water molecules attached to each calcium sulfate molecule.
To find the value of x, we need to calculate the number of moles of water lost and the number of moles of calcium sulfate remaining.
First, let's calculate the number of moles of water lost. We know that the mass of water lost is 0.39 g, so we can use the molar mass of water (18.015 g/mol) to convert the mass to moles:
Moles of water = Mass of water lost / Molar mass of water
= 0.39 g / 18.015 g/mol
Next, let's calculate the number of moles of calcium sulfate remaining. We know that the initial mass of gypsum is 1.87 g, and since the mass lost is due to water, the remaining mass must be calcium sulfate:
Mass of calcium sulfate = Initial mass - Mass of water lost
= 1.87 g - 0.39 g
To convert this mass to moles, we need to know the molar mass of calcium sulfate. The molar mass of calcium (Ca) is 40.08 g/mol, sulfur (S) is 32.07 g/mol, and oxygen (O) is 16.00 g/mol:
Molar mass of calcium sulfate (CaSO4) = Molar mass of Ca + Molar mass of S + (4 * Molar mass of O)
= 40.08 g/mol + 32.07 g/mol + (4 * 16.00 g/mol)
Now, we can calculate the number of moles of calcium sulfate:
Moles of calcium sulfate = Mass of calcium sulfate / Molar mass of calcium sulfate
Finally, divide the moles of water by the moles of calcium sulfate to find the value of x:
x = Moles of water / Moles of calcium sulfate
This value of x gives us the number of water molecules attached to each calcium sulfate molecule in the formula of gypsum (CaSO4.xH2O).