Exam (elaborations)
Chem 231 Final Exam Review Questions And Answers Latest Update
- Course
- CHEM 231
- Institution
- University Of Illinois - Urbana-Champaign
Chem 231 Final Exam Review Questions And Answers Latest Update
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Solution 2024/2025Pepper
Chem 231 Final Exam Review Questions And
Answers Latest Update
Recrystallization
A purification technique that uses properties of solubility to separate
impurities from the desired solid.
How does recrystallization work?
The general idea is to dissolve the sample in hot solvent, and then when the
samples cools, the solid crystallizes out of solution while impurities remain
dissolved.
Choosing a solvent for recrystallization
---> The ideal solvent should not dissolve the solid at room temperature but
should dissolve the solid when heated (at high temp).
--->The impurities should soluble in the solvent at all temperatures.
---> if use pair of solvents, the pair solvents must be miscible
How much of solvent should be used in Recrystallization?
a minimum amount of the solvent should be used to dissolve the
compound to be recrystallized.
Activated Carbon
can be used in recrystallization to remove color impurities from the solution.
Methods to initiate crystal formation
---> gently scratch the side or the bottom of the flask with a glass stirring
rod.
---> if scretching doesn't work, add small bits of solid compound to act as a
seed crystal for the rest of the crystals to grow around.
Gravity Filtration (in recrystallization exp)
, Solution 2024/2025
Pepper
uses gravity to pull the liquid through filter paper placed in a funnel,
isolating the solid on the filter paper.
Vacuum filtration (in recrystallization exp)
---> uses a vacuum to help pull the liquid through the filter paper
---> uses the Buchner funnel (the paper is need to sit flat in the funnel)
Melting point determination
a technique that can be used to identify compounds. Pure substance have
well-defined melting points which are altered by the presence of impurities
Distillation
A technique that uses different boiling points of liquids in a mixture to
separate the components.
types of distillation
---> all types of distillation differ in the components of apparatus.
---> Microscale and macroscale simple distillation
---> Microscale and macroscale fractional distillation.
Azeotrope
A liquid mixture of two or more substances that has its own constant boiling
point, different from the boiling points of its constituents and it maintains its
composition during distillation. very difficult to separate by distillation.
Macroscale Vs. microscale Simple distillation
In macroscale simple distillation, the condenser if often jacked with a
running water to keep it cool. while in microscale simple distillation, only
uses air to cool the vapor in the condenser.
Fractional distillation
adds a a fractionating column to give better separation of liquids with
similar boiling points, which is located right above the heated flask.
the process of fractionating column
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