Recrystallization

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It took about 4.295 mL of deionized water to properly dissolve 0.215 grams of potassium hydrogen tartrate. After recrystallization 0.156 grams of potassium hydrogen tartrate was recorded. Meaning that the experiment had made a 72.6% recovery while only losing 24.7% of the original weight. Once filtrated the sample was then melted. The first melting trial had a recorded average of 251.00. The second trial was recoded to have an average of 251.04. Meaning that the overall average experimental melting point was 251.02. The literature melting point of potassium hydrogen tartrate is 267.00So based on the data previously provided the percent error of the melting point was 5.99%. Meaning that the recrystallized substance isn’t fully pure. [pic 15][pic 16][pic 17][pic 18]

Works Cited

“A4 Recrystallization.” Chm346. University of Wisconsin-Madison, 1848. Web. 27 Jan. 2016.

Web.

Chakraborty,Ujjwal. “Recrystallization.” Lab handout

CHM 2210. 2016 ed. Jacksonville, 2016. Print

Answers to Post Laboratory Questions:

1. Define the following terms:

a) saturated solution: a solution that contains an equal amount of particles or solutes and solvent in the solution.

b) Supersaturated solution: a solution that contains a higher value of solute or dissolved material.

c) Solubility: a chemical property that refers to the ability of a solute dissolving in a solvent.

d) Mother liquor: the part of a solution that is left over after crystallization.

e) Precipitate: insoluble solid that emerges from a liquid solution.

2. Why is the recrystallization substance washed with solvent while on the filter?

Fresh solvent should be poured over the crystals to wash off any liquid that contains soluble impurities. If not the soluble impurities may be deposited on the crystals when the solvent evaporates

a) Why does the solvent used in this step need to be ice-cold?

If the solvent is not ice cold it may disintegrate some of the solid.

3. What prevents soluble impurities from appearing in the final product during recrystallization?

Slow gradual cooling of the solution at room temperature allows the proper size crystals to form.

4. Suppose not all solvent was removed from a recrystallized solid. What would the effect be on the melting point of the solid?

Impurities will reduce the melting point.

5. Name two ways of inducing crystallization

One way is to try scratching/rubbing a flask with a glass rod or metal spatula. Another tactic uses seed crystals.