Investigation to Identify the Formula of Hydrated Copper Sulphate and in doing so Find what x represents in the Formula CuSO4xH2O

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Matthew Dobson        01/05/2007        Mr Robertson

Chemistry

Science Coursework: Investigation to Identify the Formula of Hydrated Copper Sulphate and in doing so Find what x represents in the Formula CuSO4xH2O

Name: Matthew Dobson        

Partner: Jamie Barton?

Date(s) Conducted: 23/04/05 – 06/05/05

Topic: Chemistry – Moles and Empirical Formulas

Experiment:         The Degree of Hydration of Copper (II) Sulfate, CuSO4 · xH2O

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.

Apparatus:

        

MATERIALS:        Hydrated copper (II) sulphate

GENERAL:        

  •  Heatproof mat,
  •  Tripod,
  •  Bunsen burner,
  •  Pipe clay triangle,
  •  Crucible,
  •  Metal tongs,
  •  Glass mixing rod,
  •  Spatula,
  •  Electronic-Balance

 

SAFETY:        Lab coat and safety glasses to be worn at all times and care to be taken when handling hot objects.


Method:

  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 sulphate.
  6. Heat until powder has gone white but do not heat until it starts going black or yellow.
  7. Allow cooling period.
  8. Weigh.
  9. Reheat for a few minutes.
  10. Allow cooling period.
  11. Re-weigh to make sure reaction has finished.
  12. Find formulas.

        AMMENDMENTS/ADDITIONS/SAFETY PRECAUTIONS:

  • If required, manipulate CuSO4 · xH2O with glass rod during heating to assist process.
  • 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).
  • Ensure to control Bunsen flame to avoid blackening pipe clay triangle or crucible.
  • Weigh after reaction then heat again and re-weigh to make sure reaction has finished.
  • Wear Goggles at all times during practical.
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Scientific Knowledge:

  • 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.
  • Constant mass- the vessel need to be weighed at the beginning to find the original mass, then heated, allowed to cool, then weighed, then reheated and allowed to cool again before weighing again, this allows us to make sure ...

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