Lab Midterm Flashcards
(30 cards)
What is meant by the term bumping?
sudden and uncontrolled boiling of liquid
Identify necessary precautions when carrying out a vacuum filtration with organic materials
inspect the glassware for cracks or chips prior to use
What is the purpose of the solvent trap in a vacuum filtration setup?
Keeping the running water from the sink away from the filtration apparatus, and keeping the filtered materials in the filtration apparatus
Which solvent should be used to wash the solid material collected from a filtration?
The same solvent as the liquid in the original mixture
What modifications to a simple distillation setup can be made in order to increase the speed or efficiency of the separation?
Place the receiving flask in an ice bath.
After an organic reaction involving an aqueous solution, the organic solution might be washed with a saturated sodium chloride aqueous solution, known as brine. What is the purpose of the brine wash?
To reduce the amount of water in the organic solution
Identify the best support for a separatory funnel.
Iron ring clamped to a ring stand
What is the visual indicator that enough of a drying agent, such as anhydrous
MgSO4or CaCl2, has been added to properly dry an organic solution?
The drying agent will move freely like a powder around the solution.
After drying an organic solution, what methods can be used to remove the drying agent from solution?
Decanting
When working in a fume hood, what is the best position of the hood sash?
As low as possible, no more than halfway up
In this organic chemistry lab, why do we determine melting points?
It helps to determine the purity or identity of a sample.
What is the “eutectic point”?
The lowest melting point of a mixture of two different compounds
Fill in the blank. The melting point of a compound is a _________ property.
physical
Why does an impurity broaden a “melting range”?
The impurity disrupts the molecular interactions in different areas of the sample.
Why shouldn’t you reuse a sample that was previously melted, even though it has solidified again?
Some of the sample may have decomposed at or near the melting point
When selecting a suitable solvent for recrystallization, chemists use what general “rule”?
Like dissolves like
Complete the following statement with the correct sequence of words: A suitable recrystallizing solvent is one in which the chemical to be purified is relatively ____________ at low temperature and completely at or near the boiling point of the solvent.”
insoluble, soluble
What is the purpose of a hot filtration?
A hot filtration is used to remove insoluble impurities
Fill in the blanks with the correct word(s): Slow cooling of a solution will produce crystals.
large, pure
When crystals are filtered, why should you wash them with cold solvent?
To remove any remaining solvent, which may contain impurities
What does the term “immiscible” mean?
insoluble
Why do water and cyclohexame form two layers when mixed?
Water is polar and cyclohexane is nonpolar
What is the process of adding brine to a two-phase mixture called?
salting out
What is an “emulsion”?
A dispersion of very small droplets of one liquid in another, which are not soluble.
