Investigation to Identify the Formula of Hydrated Copper Sulphate
Aim: I plan to investigate the formula of Hydrated Copper Sulphate
and, more importantly, what x stands for in the formula (CuSO4.xH2O).
This will tell me how many molecules of water surround each molecule
of Copper Sulphate. To do this I plan to work out the amount of water
a set mass of Hydrated Copper Sulphate loses when it becomes
anhydrous. I will work this out by measuring the difference in mass
between the two states. And thus ascertain the degree of hydration.
I predict that because it is hydrated copper sulphate and it is blue
that it will contain water of crystallization surrounding the copper
sulphate. The number of water molecules per copper sulphate molecule
should fall somewhere between 1 and 5 as 1:5 is the largest ratio of
copper sulphate to water this molecule can contain.
MATERIALS: Hydrated copper (II) sulphate
Â§ Heatproof mat,
Â§ Bunsen burner,
Â§ Pipe clay triangle,
Â§ Metal tongs,
Â§ Glass mixing rod,
SAFETY: Lab coat and safety glasses to be worn at all times
and care to be taken when handling hot objects.
1. Set up apparatus as shown in the diagram.
2. Find the mass of crucible by itself.
3. Place 2-3 spatulas of Copper sulphate into the crucible.
4. Find the mass of the crucible and copper sulphate.
5. Work out the difference in mass to find the mass of the copper
6. Heat until powder has gone white but do not heat until it
starts going black or yellow.
7. Allow cooling period.
9. Reheat for a few minutes.
10. Allow cooling period.
11. Re-weigh to make sure reaction has finished.
12. Find formulas.
Â· If required, manipulate CuSO4 Â· xH2O with glass rod during heating
to assist process.
Â· Ensure that heating is gentle (as indicated) to avoid either damage
to the crucible or overheating the sample (this could result in
impurities in the anhydrous compound).
Â· Ensure to control Bunsen flame to avoid blackening pipe clay
triangle or crucible.
Â· Weigh after reaction then heat again and re-weigh to make sure
reaction has finished.
Â· Wear Goggles at all times during practical.
Â§ I have chosen the method I have as compounds with water of
crystallization have very weak bonds between the crystallization
surrounding the central CuSO4. Heat will remove these bonds leaving
behind just the CuSO4 in its place. The drop in mass then allows us to
calculate the ratio of CuSO4 to water.
Â§ Constant mass-...