A sample of a hydrate of CuSO4 with a mass of 250 grams was heated until all the water was removed. The sample was then weighed and found to have a mass of 160 grams. What is the formula for the hydrate?
CuSO4 * 10 H2O
CuSO4 * 7 H2O
CuSO4 * 5 H2O
CuSO4 * 2 H2O
CuSO4 * H2O
I'd take the difference between the hydrated and dehydrated sample and then divide by the molar mass of one water molecule H2O. Like so:
(250 grams - 160 grams)/Molar Mass H2O
This will allow me to find out how many water molecules there were.
CuSO4 * 5 H2O
To determine the formula of the hydrate, we need to find the molar mass of the compound with water and without water.
1. Start by finding the molar mass of CuSO4 (copper(II) sulfate):
- CuSO4: Cu (atomic mass = 63.55 g/mol) + S (atomic mass = 32.07 g/mol) + 4 * O (atomic mass = 16.00 g/mol)
- Molar mass of CuSO4 = 63.55 + 32.07 + (4 * 16.00) = 159.61 g/mol
2. Next, find the molar mass of water (H2O):
- H2O: 2 * H (atomic mass = 1.01 g/mol) + O (atomic mass = 16.00 g/mol)
- Molar mass of H2O = (2 * 1.01) + 16.00 = 18.02 g/mol
3. Calculate the number of moles of the hydrate without water:
- Mass of the hydrate without water = 160 grams
- Moles of the hydrate without water = Mass / Molar mass
- Moles of the hydrate without water = 160 g / 159.61 g/mol = 1.002 moles
4. Calculate the number of moles of water lost:
- Mass of water lost = Mass with water - Mass without water
- Mass of water lost = 250 g - 160 g = 90 g
- Moles of water lost = Mass of water lost / Molar mass of water
- Moles of water lost = 90 g / 18.02 g/mol = 4.994 moles
5. Divide the moles of water lost by the moles of the hydrate without water to find the ratio of water to the anhydrous compound:
- Ratio of water to the anhydrous compound = Moles of water lost / Moles of the hydrate without water
- Ratio of water to the anhydrous compound = 4.994 moles / 1.002 moles ≈ 5 (rounded to the nearest whole number).
6. Based on the ratio obtained, we can determine the formula of the hydrate:
- CuSO4 * 5 H2O (Copper(II) sulfate pentahydrate)
Well, it seems like the copper sulfate got a little thirsty and lost some water weight. How rude of it! To find the formula for the hydrate, we need to figure out how many water molecules were hanging out with each copper sulfate molecule.
By subtracting the mass of the anhydrous salt from the initial mass of the hydrate, we can determine the mass of the water lost. In this case, the water loss is 250 grams - 160 grams, which equals 90 grams.
Now comes the fun part! We need to find the number of moles of water lost. Since the molar mass of water is approximately 18 grams/mol, we can divide the mass of water lost by the molar mass to obtain the number of moles. In this case, 90 grams / 18 grams/mol equals 5 moles of water lost.
Based on this result, we can conclude that the formula for the hydrate is CuSO4 * 5 H2O. So, the copper sulfate molecule was kicking it with 5 water molecules.