AP Chemistry Lab: Analysis of Alum Essay Example
AP Chemistry Lab: Analysis of Alum Essay Example

AP Chemistry Lab: Analysis of Alum Essay Example

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Objective: In this lab we will analyze alum by two techniques in order to verify its identity.  The melting point and the mole ratio of hydrated water to anhydrous aluminum potassium sulfate will be determined.

Lab Procedure:

  1. Use a mortar and pestle to crush alum.
  2. Pack the alum in capillary tube, and then fasten it to the thermometer.
  3. Fasten the thermometer to the ring stand.
  4. Immerse the bottom of the capillary tube and thermometer in a beaker of water.
  5. Record the temp at which alum melts, then repeat with a new capillary tube.
  6. Set up the Bunsen burner, adjust ring clamp to 1 cm above the burner.
  7. Heat crucible over flame until red hot, then turn off gas and remove burner.
  8. Use tongs to move crucible and cool down.
  9. Find mass using balance, record data.
  10. Add 2g alum to crucib
    ...

    le, weigh and record mass.

  11. Set on burner, heat with cover loose for 5 minutes.
  12. Use tongs to remove the crucible and allow it to cool.
  13. Measure and record the data for the mass.
  14. Repeat until constant mass is obtained, recording data.
  15. Dispose of the alum, clean crucible and cover.
  16. Pre Lab Questions:

    • Melting point is the range it begins when the compound first starts to turn to liquid, and it should only be within a few degrees. However if the temperature is raised too fast, the initial reading will be missed and it would not be very accurate, therefore it is necessary to raise the temperature very slowly for accuracy.
    • There are 10 moles of water present per one mole of sodium bicarbonate present in washing soda.

    Post Lab Questions:

    1. The temperature difference between an object
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and the ambient temperature will generate convection currents in the air around the object. This will cause the reading on a sensitive balance to be unsteady and therefore inaccurate.

  • The melting point of alum is 92. 5°C, and our data of 95°C is close to it. Also,
  • A sulfate test, colorimetric determination of aluminum test, and determination of aluminum in alum test could be used to verify the composition of alum.
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