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Chemistry LibreTexts

Unknown Crystal Synthesis

  • Page ID
    150564
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    INTRODUCTION

    In this experiment, a complex substance will be synthesized that will be used throughout the semester. The remaining experiments utilize a variety of quantitative techniques that will be used to aid you in first discovering what the crystals are made of, and then determining the exact chemical formula for the unknown. The objective of the first experiment is to create the unknown crystals.

    Week 1


    Step 1.1

    Amber bottle labeled, "Crystals, Unknown A"

    Before beginning this exercise, be sure to have completed a Table of Contents in your laboratory notebook as instructed. Leave couple of pages for the table of contents, and then start on the next page for Experiment 1.

    Obtain in a clean 50mL beaker and some amount of stock solution containing unknown A solution from the pump dispenser.

     

     

     

     

     

     

    Step 1.2

    Obtain a vial with some amount of unknown B and pour all of unknown B into a clean dry 50mL beaker. Add some amount of RO water and warm on a hot plate stirring constantly until the solid is completely dissolved.


    unknown B.pngunknown B stirring.png

    Step 1.3

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    Using crucible tongs (be careful to avoid spillage) or a paper towel loop to handle the hot beaker, pour the hot solution into the beaker containing the unknown A solution and stir. Cool the solution for some good amount of time by placing the 50 mL beaker in a 250 mL beaker containing ice and water. Crystals should form during this time. Take care that the beaker of product does not sink in the ice water.

     

     

     

     

     

     

     

     

    Step 1.4

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    After giving the crystals ample time to form, carefully pour off and discard the solvent without removing any crystals, a process called decantation. Describe the crystals and record any observations.

    Add some RO water to the crystals, and heat gently with stirring to completely dissolve the crystals. If some dark residue remains undissolved, carefully decant the clear solution into another beaker and discard the residue.

    Step 1.5

    Cover the beaker with a watch glass and set in your desk drawer until the next laboratory period to allow crystals to form. If the solution is moved or stirred while crystals are forming, smaller crystals will result.

    Clean a small brown bottle. Allow it to drain and air dry in your desk for a week, or dry it carefully with a paper towel.

     

     

     

     

    The first week of the experiment ends here.

     

    Week 2


    Step 2.1

    filteration system.png

    After the crystals have been sitting for a week, set up the vacuum filtration system(See Appendix III).

    Filter the liquid and crystals by vacuum filtration with a Buchner funnel and a clean filter flask. If the crop of crystals appears to be quite small, save the filtrate so that a second crop of crystals can be obtained. Consult your instructor for the procedure.

    Wash the crystals few times with some small amount of acetone

     

     

     

     

     

     

    Step 2.2

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    Spread the crystals in bottom of a clean dry 250 mL beaker. Set aside dry in your drawer.

    When the crystals are completely dry, place them in the amber bottle, screw on the lid.

     

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