7 Procedure

• What are the steps for constant weighing of a crucible and cover?

  1. Wash/clean crucibles and cover.
  2. Heat in an oven at 110°C for 30 minutes.
  3. Cool in a desiccator for 15 minutes.
  4. Obtain the weight.
  5. Avoid holding with bare hands.
  6. Dry again at 110°C for 20 minutes.
  7. Repeat until constant weight is obtained (difference ≤ 0.001 g).
• What is the first step in the constant weighing of a crucible and cover?

  Thoroughly wash/clean a set of crucibles and cover.
• At what temperature should the cleaned crucible and cover be placed in the oven?

  110°C
• How long should the crucible and cover be left in the oven?

  30 minutes
• What should be done after removing the crucible and cover from the oven?

  Transfer them into a desiccator using crucible tongs and allow them to cool for 15 minutes.
• Why should you never hold the crucible with your bare hands during the weighing process?

  Because you can add more moisture to the container.
• What should be done after weighing the crucible and cover?

  Place them slightly ajar in an oven set at 110°C and allow them to dry again for 20 minutes.
• How many times should the cooling and heating process be repeated?

  Until a constant weight is obtained, with a difference between two successive weighings of ≤ 0.001 g.
• What is the maximum allowable difference between two successive weighings to consider the weight constant?

  ≤ 0.001 g
• Analysis of a known hydrate

  1. Weigh accurately 2 - 3 g of the hydrated CusO into the pre-weighed crucible with cover.
  2. Record the weight of the sample.
  3. Place the crucible with the sample in an oven set at 220°C for two hours.
  4. The crucible with the sample should have its cover slightly ajar while inside the oven.
  5. After one hour, cover the crucible and transfer to a desiccator.
• Analysis of a known hydrate

  • Step 6. Allow the sample to cool inside the desiccator for 15 minutes.
  • Step 7. Take note of the weight of the crucible with cover and sample.
  • Step 8. Do not open the crucible during the weighing process.
  • Step 9. Repeat the cooling and heating process until a constant weight is obtained difference between two successive weighing ≤ 0.001 9).