RP10 - Preparation of organic solids and liquids Flashcards

1
Q

What are the main steps in producing a pure organic

solid?

A
  1. Synthesis of the compound (usually using reflux, distillation etc.)
  2. Filtration (usually vacuum filtration)
  3. Purification (recrystallisation)
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2
Q

How do you use laboratory equipment to heat under

reflux?

A

Quickfit apparatus is used to heat a substance under reflux.

  • The substance is boiled in a pear-shaped or round-bottomed flask.
  • As it evaporates, it is cooled by the water in the liebig condenser and so condenses back into a liquid and drips back down into the flask to be heated again.
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3
Q

Why is heating under reflux used?

A

● Allows heating for a long period of time
● Prevents the flask from boiling dry
● Prevents volatile reactants/products escaping
● Ensures even heating

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4
Q

Why are anti-bumping granules used when heating

under reflux and distillation?

A

To allow smooth boiling- they prevent splashing up the sides of the flask due to
bubbles caused by vapours.

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5
Q

How do you use laboratory equipment to filter under

reduced pressure?

A

Using a Buchner funnel and Buchner flask, connected by rubber tubing to the vacuum source.
● The funnel contains a layer of filter paper.
● Pour the substance onto the filter paper and the liquid will be sucked through via vacuum filtration into the flask.
● The solid will remain on the paper.

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6
Q

How do you purify a solid product?

A

By recrystallisation.
● Add minimum amount of warm solvent to the impure
sample until it has dissolved.
● Allow to cool, crystals should form.
● When no more form you can filter under reduced pressure to obtain a dry crystalline solid.

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7
Q

How do you determine the melting point of a substance and why can this information be useful?

A

● Place a small sample of the solid in a capillary tube.
● Melt using the melting apparatus available, measuring the temperature with a thermometer.
● A pure substance will usually melt at a single temperature but an impure substance will melt over a range of temperatures
(usually lower than the pure substance).
● Record the starting and ending points of the melting, when the first crystal can be seen to melt and when the last crystal becomes liquid respectively.
● You can then compare the melting point to known values to identify the
substance.

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8
Q

How do you purify a liquid organic product?

A

● You can use a separating funnel to isolate the organic layer from the aqueous layer.
● Add anhydrous MgSO4
to the organic product to
get rid of all water.
● You can then purify the liquid by distillation, which
separates the substances by boiling point.

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9
Q

How do you calculate the percentage yield of a product?

A

Percentage yield =

Actual yield/ theoretical yield x100

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